View Full Version : Re: ekpyrotic/cyclic big bang scenario
Thomas Dent
Jun16-04, 05:56 AM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>Ulmo <ulmo@cheerful.com> wrote\n\n> > ...Now Steinhardt and Turok say that - according to \'M-theory\' - the\n> > universe need not pass through a singularity between a big crunch and\na\n> > big bang.\n>\n> This is Steinhardt\'s claim, but it\'s a tiny minority of cosmologists\n> who follow it because in cyclical cosmology, it\'s still passing\n> through a singularity, even if you try to call it something else. The\n> brane collision is a singularity by another name.\n\nThe problem is that the collision is not calculable. Presumably if you\nset up a spacetime where two branes were heading for a collision in\nthe required fashion the whole thing would work out somehow, but the\nquestion is, how? (One can\'t calculate in M-theory because the\nunderlying theory is not known!)\n\nAlso, Steinhardt et al. don\'t have a specific string model: they just\nassume that some kind of branes exist which have the properties they\nwant. To be fair, lots of real string theorists have looked at the\nproblem of colliding branes, but it is somewhat hard because there are\nno applicable exact solutions of the string equations. (Someone\ncorrect me if I\'m wrong please!)\n\nA similar problem of calculability appeared in the predecessor of\n\'cyclic\' and \'ekpyrotic\', i.e. the pre-big-bang (PBB) cosmology of\nVeneziano and Gasperini, which is quite similar to one cycle of cyclic\nwithout the branes (as it were). PBB starts off with a large, flat,\ncold Universe and then (almost certainly) requires we pass through a\nregion of strong coupling and large spacetime curvature, which results\nin large, currently uncalculable corrections to whatever effective\ntheory we try to use. Cyclic/ekpyrotic has the advantage that you can\ndo it in flat space, but the disadvantage that you have branes which\nbehave messily when they get close to each other and collide.\n\n> In cyclic\n> cosmology, the universe expands, collapses, goes through a Big\n> Crunch/Big Bang, expands, collapses, goes through a Big Crunch/Big\n> Bang, and repeats this an infinite number of times. It would actually\n> pass through an infinite number of singularities. Yeah, it would also\n> be a perpetual motion machine, which is another argument against it.\n> Once at a physics conference. Steinhardt was defending his cyclical\n> model, and suddenly Susskind stood up and shouted, "That\'s a perpetual\n> motion machine of the second kind!".\n\nTechnically, it is not quite a "Big Crunch", which implies that the\nscale factor goes to zero and curvature diverges, it is a special\nfive-dimensional pseudo-singularity which does not involve divergent\ncurvature.\n\nIt was a nice line, but Susskind is wrong if he wants to say this is a\nfatal objection. It is easy to answer. The cyclic universe is not a\nclosed system where the entropy kills you (which was the problem with\nthe cyclic closed Tolman universe which had higher entropy at each\nsuccessive bounce). The scale factor expands exponentially between\neach cycle, the entropy created at each collision is diluted\nenormously during the ensuing slow expansion. Globally it is like a de\nSitter space with occasional "hiccups" where the branes collide, the\nexpansion temporarily decelerates, additional entropy is produced and\nthe formation of structure occurs.\n\nOne possibly more valid objection is that the repetition from one\ncycle to the next will not be exact due to fluctuations. Hence one\nneeds to construct the model so that it has a stable cyclic attractor\n(as in the theory of dynamical systems). But if the attractor is\nstable (i.e. deviations from the attractor decrease) in going from\ncycle N to cycle N+1, it is unstable with respect to going from N to\nN-1. Stable in the future implies unstable in the past. Hence at some\npoint in the past, the Universe must have diverged from the cycle by\nan arbitrarily large amount. Unless the whole phase space is free of\ndangerous singularities (which is unlikely given the deep negative\nminimum of the potential), they still need to set up some initial\nconditions. It doesn\'t solve the metaphysical problem of initial\nconditions!\n\nBut concerning what is actually observable, I suppose they can assume\nwe are enough cycles away from the initial divergent period that it\nmakes no difference.\n\nT\n\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>Ulmo <ulmo@cheerful.com> wrote
> > ...Now Steinhardt and Turok say that - according to 'M-theory' - the
> > universe need not pass through a singularity between a big crunch and
a
> > big bang.
>
> This is Steinhardt's claim, but it's a tiny minority of cosmologists
> who follow it because in cyclical cosmology, it's still passing
> through a singularity, even if you try to call it something else. The
> brane collision is a singularity by another name.
The problem is that the collision is not calculable. Presumably if you
set up a spacetime where two branes were heading for a collision in
the required fashion the whole thing would work out somehow, but the
question is, how? (One can't calculate in M-theory because the
underlying theory is not known!)
Also, Steinhardt et al. don't have a specific string model: they just
assume that some kind of branes exist which have the properties they
want. To be fair, lots of real string theorists have looked at the
problem of colliding branes, but it is somewhat hard because there are
no applicable exact solutions of the string equations. (Someone
correct me if I'm wrong please!)
A similar problem of calculability appeared in the predecessor of
'cyclic' and 'ekpyrotic', i.e. the pre-big-bang (PBB) cosmology of
Veneziano and Gasperini, which is quite similar to one cycle of cyclic
without the branes (as it were). PBB starts off with a large, flat,
cold Universe and then (almost certainly) requires we pass through a
region of strong coupling and large spacetime curvature, which results
in large, currently uncalculable corrections to whatever effective
theory we try to use. Cyclic/ekpyrotic has the advantage that you can
do it in flat space, but the disadvantage that you have branes which
behave messily when they get close to each other and collide.
> In cyclic
> cosmology, the universe expands, collapses, goes through a Big
> Crunch/Big Bang, expands, collapses, goes through a Big Crunch/Big
> Bang, and repeats this an infinite number of times. It would actually
> pass through an infinite number of singularities. Yeah, it would also
> be a perpetual motion machine, which is another argument against it.
> Once at a physics conference. Steinhardt was defending his cyclical
> model, and suddenly Susskind stood up and shouted, "That's a perpetual
> motion machine of the second kind!".
Technically, it is not quite a "Big Crunch", which implies that the
scale factor goes to zero and curvature diverges, it is a special
five-dimensional pseudo-singularity which does not involve divergent
curvature.
It was a nice line, but Susskind is wrong if he wants to say this is a
fatal objection. It is easy to answer. The cyclic universe is not a
closed system where the entropy kills you (which was the problem with
the cyclic closed Tolman universe which had higher entropy at each
successive bounce). The scale factor expands exponentially between
each cycle, the entropy created at each collision is diluted
enormously during the ensuing slow expansion. Globally it is like a de
Sitter space with occasional "hiccups" where the branes collide, the
expansion temporarily decelerates, additional entropy is produced and
the formation of structure occurs.
One possibly more valid objection is that the repetition from one
cycle to the next will not be exact due to fluctuations. Hence one
needs to construct the model so that it has a stable cyclic attractor
(as in the theory of dynamical systems). But if the attractor is
stable (i.e. deviations from the attractor decrease) in going from
cycle N to cycle N+1, it is unstable with respect to going from N to
N-1. Stable in the future implies unstable in the past. Hence at some
point in the past, the Universe must have diverged from the cycle by
an arbitrarily large amount. Unless the whole phase space is free of
dangerous singularities (which is unlikely given the deep negative
minimum of the potential), they still need to set up some initial
conditions. It doesn't solve the metaphysical problem of initial
conditions!
But concerning what is actually observable, I suppose they can assume
we are enough cycles away from the initial divergent period that it
makes no difference.
T
Urs Schreiber
Jun16-04, 02:34 PM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>On Wed, 16 Jun 2004, Thomas Dent wrote:\n\n> The problem is that the collision is not calculable. Presumably if you\n> set up a spacetime where two branes were heading for a collision in\n> the required fashion the whole thing would work out somehow, but the\n> question is, how? (One can\'t calculate in M-theory because the\n> underlying theory is not known!)\n\nWhat would be the next best toy example approximating the real thing while\nstill being calculable?\n\n\n> Technically, it is not quite a "Big Crunch", which implies that the\n> scale factor goes to zero and curvature diverges, it is a special\n> five-dimensional pseudo-singularity which does not involve divergent\n> curvature.\n\nBTW, since we recently had here a discussion involving the question of big\ncrunch solutions in string theory. Today in\n\nT. Hertog & T. Horowitz,\nTowards a Big Crunch Dual\nhep-th/0406134\n\nit is attemted to study that question from the dual CFT point of view. The\nresults remain vague, but apparently there is evidence that for certain\nboundary conditions there are CFTs which have well-defined time evolution\nonly for a finite amount of time. Since the CFT is supposed to capture the\nnon-perturbative dynamics of the dual string theory this would imply that\ncosmological singularities such as big crunches occur even in full\nM-theory, somehow. But apparently this result has to be taken with a\ngrain of salt.\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>On Wed, 16 Jun 2004, Thomas Dent wrote:
> The problem is that the collision is not calculable. Presumably if you
> set up a spacetime where two branes were heading for a collision in
> the required fashion the whole thing would work out somehow, but the
> question is, how? (One can't calculate in M-theory because the
> underlying theory is not known!)
What would be the next best toy example approximating the real thing while
still being calculable?
> Technically, it is not quite a "Big Crunch", which implies that the
> scale factor goes to zero and curvature diverges, it is a special
> five-dimensional pseudo-singularity which does not involve divergent
> curvature.
BTW, since we recently had here a discussion involving the question of big
crunch solutions in string theory. Today in
T. Hertog & T. Horowitz,
Towards a Big Crunch Dual
http://www.arxiv.org/abs/hep-th/0406134
it is attemted to study that question from the dual CFT point of view. The
results remain vague, but apparently there is evidence that for certain
boundary conditions there are CFTs which have well-defined time evolution
only for a finite amount of time. Since the CFT is supposed to capture the
non-perturbative dynamics of the dual string theory this would imply that
cosmological singularities such as big crunches occur even in full
M-theory, somehow. But apparently this result has to be taken with a
grain of salt.
Thomas Dent
Jun17-04, 05:24 AM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>Urs Schreiber <Urs.Schreiber@uni-essen.de> wrote\n\n> On Wed, 16 Jun 2004, Thomas Dent wrote:\n>\n> > The problem is that the collision is not calculable. Presumably if you\n> > set up a spacetime where two branes were heading for a collision in\n> > the required fashion the whole thing would work out somehow, but the\n> > question is, how?\n>\n> What would be the next best toy example approximating the real thing while\n> still being calculable?\n\nAs I hinted in my over-5000-byte message, I remember vaguely that\nstring people were studying time-dependent orbifolds of flat space\nabout 2 years ago. It might have involved someone called N*th*n\nS**b*rg. I don\'t remember what the exact results were. It seems they\ndid not include branes. Other people may have tried to calculate\nsomething with colliding or intersecting branes in flat space.\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>Urs Schreiber <Urs.Schreiber@uni-essen.de> wrote
> On Wed, 16 Jun 2004, Thomas Dent wrote:
>
> > The problem is that the collision is not calculable. Presumably if you
> > set up a spacetime where two branes were heading for a collision in
> > the required fashion the whole thing would work out somehow, but the
> > question is, how?
>
> What would be the next best toy example approximating the real thing while
> still being calculable?
As I hinted in my over-5000-byte message, I remember vaguely that
string people were studying time-dependent orbifolds of flat space
about 2 years ago. It might have involved someone called N*th*nS**b*rg. I don't remember what the exact results were. It seems they
did not include branes. Other people may have tried to calculate
something with colliding or intersecting branes in flat space.
Urs Schreiber
Jun17-04, 05:34 AM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>"Thomas Dent" <tdent@auth.gr> schrieb im Newsbeitrag\nnews:cb504c2c.0406170212.4d6b785d-100000@posting.google.com...\n> Urs Schreiber <Urs.Schreiber@uni-essen.de> wrote\n\n> > What would be the next best toy example approximating the real thing\nwhile\n> > still being calculable?\n\n> Other people may have tried to calculate\n> something with colliding or intersecting branes in flat space.\n\nA couple of days ago in the message\n\nhttp://groups.google.de/groups?selm=2iosqmFpp5poU1-100000%40uni-berlin.de\n\nRobert Helling mentioned some aspects of brane interactions as they are\ndealt with in intersecting brane models. Does this have any bearing on the\nissues of _colliding_ branes? At least it seems to indicate that generically\ntwo colliding branes will rip apart, by "recombination", doesn\'t it?\n\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>"Thomas Dent" <tdent@auth.gr> schrieb im Newsbeitrag
news:cb504c2c.0406170212.4d6b785d-100000@posting.google.com...
> Urs Schreiber <Urs.Schreiber@uni-essen.de> wrote
> > What would be the next best toy example approximating the real thing
while
> > still being calculable?
> Other people may have tried to calculate
> something with colliding or intersecting branes in flat space.
A couple of days ago in the message
http://groups.google.de/groups?selm=2iosqmFpp5poU1-100000%40uni-berlin.de
Robert Helling mentioned some aspects of brane interactions as they are
dealt with in intersecting brane models. Does this have any bearing on the
issues of _colliding_ branes? At least it seems to indicate that generically
two colliding branes will rip apart, by "recombination", doesn't it?
Thomas Dent
Jun17-04, 04:24 PM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>Urs Schreiber <Urs.Schreiber@uni-essen.de> wrote\n\n> > Other people may have tried to calculate\n> > something with colliding or intersecting branes in flat space.\n>\n> A couple of days ago in the message\n>\n> http://groups.google.de/groups?selm=2iosqmFpp5poU1-100000%40uni-berlin.de\n>\n> Robert Helling mentioned some aspects of brane interactions as they are\n> dealt with in intersecting brane models. Does this have any bearing on the\n> issues of _colliding_ branes? At least it seems to indicate that generically\n> two colliding branes will rip apart, by "recombination", doesn\'t it?\n\nI\'m not sure what you mean here. In the cyclic/ekpyrotic ideal the\nbranes are infinite over all 4-space and parallel or very nearly so in\nthe extra dimension.\n\n---v-----------v-----v---------\n\n---------v---------v--------v--\n\nwhere v represents a perturbation. They collide and ... and what, is\nthe question. If they were brane and antibrane then they could\nannihilate into radiation or defects of some sort.\n\n--------v--------v-- -> --------\\ /------\\ /--\n--------^--------^-- ________/ \\______/ \\__\n\nRather odd, really. (Actually Henry Tye and collaborators, among\nothers, have done work on the aftermath of \'brane inflation\' which is\nsimilar in that it involves colliding branes.)\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>Urs Schreiber <Urs.Schreiber@uni-essen.de> wrote
> > Other people may have tried to calculate
> > something with colliding or intersecting branes in flat space.
>
> A couple of days ago in the message
>
> http://groups.google.de/groups?selm=2iosqmFpp5poU1-100000%40uni-berlin.de
>
> Robert Helling mentioned some aspects of brane interactions as they are
> dealt with in intersecting brane models. Does this have any bearing on the
> issues of _colliding_ branes? At least it seems to indicate that generically
> two colliding branes will rip apart, by "recombination", doesn't it?
I'm not sure what you mean here. In the cyclic/ekpyrotic ideal the
branes are infinite over all 4-space and parallel or very nearly so in
the extra dimension.
---v-----------v-----v---------
---------v---------v--------v--
where v represents a perturbation. They collide and ... and what, is
the question. If they were brane and antibrane then they could
annihilate into radiation or defects of some sort.
--------v--------v-- -> --------\ /------\ /--
--------^--------^-- __{______}/ \__{____}/ \__
Rather odd, really. (Actually Henry Tye and collaborators, among
others, have done work on the aftermath of 'brane inflation' which is
similar in that it involves colliding branes.)
Urs Schreiber
Jun18-04, 04:26 AM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>"Thomas Dent" <tdent@auth.gr> schrieb im Newsbeitrag\nnews:cb504c2c.0406171159.46eb11fa-100000@posting.google.com...\n> Urs Schreiber <Urs.Schreiber@uni-essen.de> wrote\n>\n> > > Other people may have tried to calculate\n> > > something with colliding or intersecting branes in flat space.\n> >\n> > A couple of days ago in the message\n> >\n> >\nhttp://groups.google.de/groups?selm=2iosqmFpp5poU1-100000%40uni-berlin.de\n> >\n> > Robert Helling mentioned some aspects of brane interactions as they are\n> > dealt with in intersecting brane models. Does this have any bearing on\nthe\n> > issues of _colliding_ branes? At least it seems to indicate that\ngenerically\n> > two colliding branes will rip apart, by "recombination", doesn\'t it?\n>\n> I\'m not sure what you mean here. In the cyclic/ekpyrotic ideal the\n> branes are infinite over all 4-space and parallel or very nearly so in\n> the extra dimension.\n\nYes, that\'s precisely what I mean. In the\nstandard-model-from-strings-on-intersecting-branes-models one has usually,\nIIRC, D6 branes filling spacetime and wrapping some 3-cycles in the internal\nCY.\n\n> where v represents a perturbation. They collide and ... and what, is\n> the question.\n\nYup.\n\n> If they were brane and antibrane then they could\n> annihilate into radiation or defects of some sort.\n\nIn the ekpyrotic scenario, are the branes supposed to be brane-antibrane\npairs? I\'d guessed that they are not (at least not stacks of the same amount\nof both species, respectively), since otherwise, as you say, they just\nannihilate. But even fro D-D and \\bar D- \\bar D intersections there can be\n"recombination" for instance, which would mean that the naive brane\n\'collision\' as I got the impression is used in \'ekpyrotic thinking\' is very\nmuch oversimplified, I \'d guess. But I don\'t know.\n\n> Rather odd, really. (Actually Henry Tye and collaborators, among\n> others, have done work on the aftermath of \'brane inflation\' which is\n> similar in that it involves colliding branes.)\n\nThis refers to using the tachyon between D-\\bar D pairs as the inflaton\nfield, right? (Discussed recently at\nhttp://groups.google.de/groups?selm=c7fd6c7a.0406010651.5f3403cf-100000%40posting.google.com). Is that related to the ekpyrotic scenario?\n\n\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>"Thomas Dent" <tdent@auth.gr> schrieb im Newsbeitrag
news:cb504c2c.0406171159.46eb11fa-100000@posting.google.com...
> Urs Schreiber <Urs.Schreiber@uni-essen.de> wrote
>
> > > Other people may have tried to calculate
> > > something with colliding or intersecting branes in flat space.
> >
> > A couple of days ago in the message
> >
> >
http://groups.google.de/groups?selm=2iosqmFpp5poU1-100000%40uni-berlin.de
> >
> > Robert Helling mentioned some aspects of brane interactions as they are
> > dealt with in intersecting brane models. Does this have any bearing on
the
> > issues of _colliding_ branes? At least it seems to indicate that
generically
> > two colliding branes will rip apart, by "recombination", doesn't it?
>
> I'm not sure what you mean here. In the cyclic/ekpyrotic ideal the
> branes are infinite over all 4-space and parallel or very nearly so in
> the extra dimension.
Yes, that's precisely what I mean. In the
standard-model-from-strings-on-intersecting-branes-models one has usually,
IIRC, D6 branes filling spacetime and wrapping some 3-cycles in the internal
CY.
> where v represents a perturbation. They collide and ... and what, is
> the question.
Yup.
> If they were brane and antibrane then they could
> annihilate into radiation or defects of some sort.
In the ekpyrotic scenario, are the branes supposed to be brane-antibrane
pairs? I'd guessed that they are not (at least not stacks of the same amount
of both species, respectively), since otherwise, as you say, they just
annihilate. But even fro D-D and \bar D- \bar D intersections there can be
"recombination" for instance, which would mean that the naive brane
'collision' as I got the impression is used in 'ekpyrotic thinking' is very
much oversimplified, I 'd guess. But I don't know.
> Rather odd, really. (Actually Henry Tye and collaborators, among
> others, have done work on the aftermath of 'brane inflation' which is
> similar in that it involves colliding branes.)
This refers to using the tachyon between D-\bar D pairs as the inflaton
field, right? (Discussed recently at
http://groups.google.de/groups?selm=c7fd6c7a.0406010651.5f3403cf-100000%40posting.google.com). Is that related to the ekpyrotic scenario?
Robert C. Helling
Jun18-04, 06:58 AM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>On Thu, 17 Jun 2004 06:34:03 -0400, Urs Schreiber <Urs.Schreiber@uni-essen.de> wrote:\n\n> Robert Helling mentioned some aspects of brane interactions as they are\n> dealt with in intersecting brane models. Does this have any bearing on the\n> issues of _colliding_ branes? At least it seems to indicate that generically\n> two colliding branes will rip apart, by "recombination", doesn\'t it?\n\nActually, I have to admit, giving a lunch seminar on the ekpyrotic\nscenario is what go me interested in brane recombination. And yes, the\nprocesses are related by dualities, although they are not exactly the\nsame. Those days, we speculated (in a real stringy coffee table\ndiscussion) what would happen if the ekpyrotic scenario were true, but\nthere were further bulk branes that could collide in the near future\nwith our universe. The upshot was, that one could probably do ordinary\ncollider tests to see that doomsday is close: The idea would be that\nour low energy couplings (including masses etc, the 21 parameters of\nthe SM) all depend on (geometric) moduli of the M-Theory\ncompactification that we live in, and thus they generically also\ndepend on the position of bulk branes.\n\nNow, the expyrotic people assume a potential for the brane position\n(motivated by instanton calculations a la Harvey and Moore) that is\nexponential so that most of the time the brane moves slowly and only\nsignificantly accelerates just before the collistion. Therefore we\ncould see that another collision would be immanent if suddenly\nconstants of nature changed.\n\nTo be a bit more specific, the ekpyrotic people work in the setup up\nheterotic M-Theory, that is Horava-Witten compactified on a\nCalabi-Yau. Thus, from a five dimensional point of view (small CY but\nthe intervall is visible), the end-of-the-universe branes are 3-branes\nand susy implies for M5-branes to wrap a holomorphic 2-cylce in the\nCY. Hence, they are also 3-branes and they have to be at a point in\nthe intervall (i.e. parallel to the extended directions of the\nend-of-the-universe branes).\n\nNow, what can happen when the two types of brane meet is that the M5\nbecomes an instanton in the gauge bundle of the 9-brane. However, the\nlow energy physics of this is poorly understood. However, there is a\nstring thoery analogue: It is a D0 brane meeting a D4 brane and\nturning into an instanton in the D4-gauge theory (\'branes within\nbranes\'). One way to see that, is the WZW-term in the brane action of\nthe D4:\n\nint exp(B-F) sum_i C(i)\n\nwhere C(i) is the RR-i-form. This contains a term C(1) /\\ F /\\ F which\nimplies that int F/\\F, the instanton number gives rise to a D0-charge\nso D0-charge is preserved in the process. As this is a standard\nD-brane set-up (at least in the susy und thus static case) ordinatry\nstring calculations can be used. However, low energy gauge theory\ndescriptions differ on the two branches: On the Coulomb-branch (D0 and\nD4 separated) the description is in terms of the 1dim D0 theory with\nmassive fundamental matter (strings stretching between the branes),\nwhereas on the Higgs branch it is a 4+1 dim theory on the D4, but now\nwith a non trivial gauge bundle (i.e. an instanton). The connection\nbetween the two pictures comes about when the fundamental matter\nbecomes massless or the instanton shrinks to zero size.\n\nThe picture becomes more democratic after some T-dualities turning\nthis set-up into two D3-branes intersecting at right angles where the\nHiggs branch now is described as a brane recombination. This system\ncan be described using defect field theory and this is what we have\ndone in our paper (hep-th/0309043). There is also a seminar I gave\nabout this here\n\nhttp://www.damtp.cam.ac.uk/user/rch47/try.pdf\n\nFinally let me mention (as there was some confusion in some other post\nto this thread) that branes at angles (or curved branes) generalize\nthe concept of branes vs anti-branes: Two branes correspond to two\nbranes a 0 angle and of you turn one around by 180 degrees you turn\nthem into a brane anti-brane pair. So, losely speaking, any curved\nbrane bears within itself a contribution from an anti-brane.\n\nRobert\n\n\n--\n..oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oO o.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oO\nRobert C. Helling Department of Applied Mathematics and Theoretical Physics\nUniversity of Cambridge\nprint "Just another Phone: +44/1223/766870\nstupid .sig\\n"; http://www.aei-potsdam.mpg.de/~helling\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>On Thu, 17 Jun 2004 06:34:03 -0400, Urs Schreiber <Urs.Schreiber@uni-essen.de> wrote:
> Robert Helling mentioned some aspects of brane interactions as they are
> dealt with in intersecting brane models. Does this have any bearing on the
> issues of _colliding_ branes? At least it seems to indicate that generically
> two colliding branes will rip apart, by "recombination", doesn't it?
Actually, I have to admit, giving a lunch seminar on the ekpyrotic
scenario is what go me interested in brane recombination. And yes, the
processes are related by dualities, although they are not exactly the
same. Those days, we speculated (in a real stringy coffee table
discussion) what would happen if the ekpyrotic scenario were true, but
there were further bulk branes that could collide in the near future
with our universe. The upshot was, that one could probably do ordinary
collider tests to see that doomsday is close: The idea would be that
our low energy couplings (including masses etc, the 21 parameters of
the SM) all depend on (geometric) moduli of the M-Theory
compactification that we live in, and thus they generically also
depend on the position of bulk branes.
Now, the expyrotic people assume a potential for the brane position
(motivated by instanton calculations a la Harvey and Moore) that is
exponential so that most of the time the brane moves slowly and only
significantly accelerates just before the collistion. Therefore we
could see that another collision would be immanent if suddenly
constants of nature changed.
To be a bit more specific, the ekpyrotic people work in the setup up
heterotic M-Theory, that is Horava-Witten compactified on a
Calabi-Yau. Thus, from a five dimensional point of view (small CY but
the intervall is visible), the end-of-the-universe branes are 3-branes
and susy implies for M5-branes to wrap a holomorphic 2-cylce in the
CY. Hence, they are also 3-branes and they have to be at a point in
the intervall (i.e. parallel to the extended directions of the
end-of-the-universe branes).
Now, what can happen when the two types of brane meet is that the M5
becomes an instanton in the gauge bundle of the 9-brane. However, the
low energy physics of this is poorly understood. However, there is a
string thoery analogue: It is a D0 brane meeting a D4 brane and
turning into an instanton in the D4-gauge theory ('branes within
branes'). One way to see that, is the WZW-term in the brane action of
the D4:
\int \exp(B-F) sum_i C(i)
where C(i) is the RR-i-form. This contains a term C(1) /\ F /\ F which
implies that \int F/\F, the instanton number gives rise to a D0-charge
so D0-charge is preserved in the process. As this is a standard
D-brane set-up (at least in the susy und thus static case) ordinatry
string calculations can be used. However, low energy gauge theory
descriptions differ on the two branches: On the Coulomb-branch (D0 and
D4 separated) the description is in terms of the 1dim D0 theory with
massive fundamental matter (strings stretching between the branes),
whereas on the Higgs branch it is a 4+1 dim theory on the D4, but now
with a non trivial gauge bundle (i.e. an instanton). The connection
between the two pictures comes about when the fundamental matter
becomes massless or the instanton shrinks to zero size.
The picture becomes more democratic after some T-dualities turning
this set-up into two D3-branes intersecting at right angles where the
Higgs branch now is described as a brane recombination. This system
can be described using defect field theory and this is what we have
done in our paper (http://www.arxiv.org/abs/hep-th/0309043). There is also a seminar I gave
about this here
http://www.damtp.cam.ac.uk/user/rch47/try.pdf
Finally let me mention (as there was some confusion in some other post
to this thread) that branes at angles (or curved branes) generalize
the concept of branes vs anti-branes: Two branes correspond to two
branes a angle and of you turn one around by 180 degrees you turn
them into a brane anti-brane pair. So, losely speaking, any curved
brane bears within itself a contribution from an anti-brane.
Robert
--
..oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo. oOo.oOo.oOo.oOo.oOo.oOo.oOo.oO
Robert C. Helling Department of Applied Mathematics and Theoretical Physics
University of Cambridge
print "Just another Phone: +44/1223/766870
stupid .sig\n"; http://www.aei-potsdam.mpg.de/~helling
Urs Schreiber
Jun18-04, 01:56 PM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>On Fri, 18 Jun 2004, Robert C. Helling wrote:\n\n> Now, the expyrotic people assume a potential for the brane position\n> (motivated by instanton calculations a la Harvey and Moore)\n\n\nCould you expand on that? What is known about this \'motivation\'? Is the\npotential needed in order for something ekpyrotic to make sense?\n\n\n> exponential so that most of the time the brane moves slowly and only\n> significantly accelerates just before the collistion. Therefore we\n> could see that another collision would be immanent if suddenly\n> constants of nature changed.\n\n\nWhat would the relevant time scales be? To stay in this picture: Would we\nhave time to slowly see the constants of nature varying, over, say,\ncenturies or something.\n\nProbably that depends on the setup, but it addresses a general question I\nhave: For instance in models where a tachyon between some brane\nconfiguration is used as the Higgs field of some phenomenological model.\nHow do I know that the decay of the branes will last long enough in order\nto give that Higgs a chance to be the Higgs that we hope to find at LHC?\n\n> To be a bit more specific, the ekpyrotic people work in the setup up\n> heterotic M-Theory,\n\n\nOh, from what Thomas said I had gotten the impression that that scenario\nis much more vaguely "string inspired" than this seems to suggest.\n\n\n> Now, what can happen when the two types of brane meet is that the M5\n> becomes an instanton in the gauge bundle of the 9-brane.\n\n\nOk, and is this possibility taken into account in ekpyrotic models. Would\nsuch models still be viable if this transformation happened?\n\n\n> string calculations can be used. However, low energy gauge theory\n> descriptions differ on the two branches: On the Coulomb-branch (D0 and\n> D4 separated) the description is in terms of the 1dim D0 theory with\n> massive fundamental matter (strings stretching between the branes),\n> whereas on the Higgs branch it is a 4+1 dim theory on the D4, but now\n\n\nSince I have a license to ask stupid questions: Could you briefly explain\nthe Coulomb-branch/Higgs-branch terminiology?\n\n\n> Finally let me mention (as there was some confusion in some other post\n> to this thread) that branes at angles (or curved branes) generalize\n> the concept of branes vs anti-branes: Two branes correspond to two\n> branes a 0 angle and of you turn one around by 180 degrees you turn\n> them into a brane anti-brane pair. So, losely speaking, any curved\n> brane bears within itself a contribution from an anti-brane.\n\n\nMany thanks for setting me straight. I appreciate it!\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>On Fri, 18 Jun 2004, Robert C. Helling wrote:
> Now, the expyrotic people assume a potential for the brane position
> (motivated by instanton calculations a la Harvey and Moore)
Could you expand on that? What is known about this 'motivation'? Is the
potential needed in order for something ekpyrotic to make sense?
> exponential so that most of the time the brane moves slowly and only
> significantly accelerates just before the collistion. Therefore we
> could see that another collision would be immanent if suddenly
> constants of nature changed.
What would the relevant time scales be? To stay in this picture: Would we
have time to slowly see the constants of nature varying, over, say,
centuries or something.
Probably that depends on the setup, but it addresses a general question I
have: For instance in models where a tachyon between some brane
configuration is used as the Higgs field of some phenomenological model.
How do I know that the decay of the branes will last long enough in order
to give that Higgs a chance to be the Higgs that we hope to find at LHC?
> To be a bit more specific, the ekpyrotic people work in the setup up
> heterotic M-Theory,
Oh, from what Thomas said I had gotten the impression that that scenario
is much more vaguely "string inspired" than this seems to suggest.
> Now, what can happen when the two types of brane meet is that the M5
> becomes an instanton in the gauge bundle of the 9-brane.
Ok, and is this possibility taken into account in ekpyrotic models. Would
such models still be viable if this transformation happened?
> string calculations can be used. However, low energy gauge theory
> descriptions differ on the two branches: On the Coulomb-branch (D0 and
> D4 separated) the description is in terms of the 1dim D0 theory with
> massive fundamental matter (strings stretching between the branes),
> whereas on the Higgs branch it is a 4+1 dim theory on the D4, but now
Since I have a license to ask stupid questions: Could you briefly explain
the Coulomb-branch/Higgs-branch terminiology?
> Finally let me mention (as there was some confusion in some other post
> to this thread) that branes at angles (or curved branes) generalize
> the concept of branes vs anti-branes: Two branes correspond to two
> branes a angle and of you turn one around by 180 degrees you turn
> them into a brane anti-brane pair. So, losely speaking, any curved
> brane bears within itself a contribution from an anti-brane.
Many thanks for setting me straight. I appreciate it!
Thomas Dent
Jun20-04, 07:55 PM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>"Robert C. Helling" <helling@ariel.physik.hu-berlin.de> wrote\n\n> Now, the expyrotic people assume a potential for the brane position\n> (motivated by instanton calculations a la Harvey and Moore) that is\n> exponential so that most of the time the brane moves slowly and only\n> significantly accelerates just before the collision. Therefore we\n> could see that another collision would be imminent if suddenly\n> constants of nature changed.\n\nExpyrotic! Yes, most of them are ex-pyrotic now.\n\n> To be a bit more specific, the ekpyrotic people work in the setup up\n> heterotic M-Theory, that is Horava-Witten compactified on a\n> Calabi-Yau. Thus, from a five dimensional point of view (small CY but\n> the intervall is visible), the end-of-the-universe branes are 3-branes\n> and susy implies for M5-branes to wrap a holomorphic 2-cycle in the\n> CY. Hence, they are also 3-branes and they have to be at a point in\n> the intervall (i.e. parallel to the extended directions of the\n> end-of-the-universe branes).\n\nHum! Ekpyrotic is actually not Horava-Witten theory. (It seems their\npropaganda was too successful.) It just looks a bit similar. Ekpyrotic\n(and cyclic) requires you be able to take the interbrane distance to\ninfinity, or at least, to be extremely large, to get the required flat\npotential. But Horava-Witten has a finite and not very large limit on\nthis distance because of the domain wall solution which becomes\nsingular at some point. (See recent work by Curio and Krause for an\nupdate.)\n\nPeople have actually done work on time-dependent solutions of real\nheterotic M-theory with 5-branes, using the laboriously derived\neffective supergravity: see recent work of Lukas. It is certainly not\nekpyrotic.\n\nBut your speculations also apply to this case, and in general to any\ncosmology with moving branes. I suppose D-branes are easier to deal\nwith.\n\n\n> Now, what can happen when the two types of brane meet is that the M5\n> becomes an instanton in the gauge bundle of the 9-brane. However, the\n> low energy physics of this is poorly understood.\n\nSo says you. This occurs in the solutions of Lukas and collaborators.\nThey are able to find an effective action for the instanton moduli:\nhttp://arxiv.org/abs/hep-th/0312111\n\n"We present the first examples of cosmological solutions to\nfour-dimensional heterotic models which include an evolving bundle\nmodulus. The particular bundle modulus we consider corresponds to the\nwidth of a gauge five brane. (...) Certain properties are generic to\nthese solutions, regardless of initial conditions. This enables us to\nmake some definite statements about the dynamics subsequent to a small\ninstanton transition despite the fact that we cannot microscopically\ndescribe the process itself. We also show that an effective\ndescription of the small instanton transition by a continuous matching\nof fields and their first derivatives is precluded by the form of the\nrespective low-energy theories before and after the transition.\n\nSo the actual moment of collision is not understood, but the aftermath\nis better under control. See also http://arxiv.org/abs/hep-th/0309096\n..\n\n> Finally let me mention (as there was some confusion in some other post\n> to this thread) that branes at angles (or curved branes) generalize\n> the concept of branes vs anti-branes: Two branes correspond to two\n> branes a 0 angle and of you turn one around by 180 degrees you turn\n> them into a brane anti-brane pair. So, losely speaking, any curved\n> brane bears within itself a contribution from an anti-brane.\n>\n> Robert\n\nNow, could this apply also to the end-of-the-world branes in M-theory?\n(E.g. Fabinger-Horava.)\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>"Robert C. Helling" <helling@ariel.physik.hu-berlin.de> wrote
> Now, the expyrotic people assume a potential for the brane position
> (motivated by instanton calculations a la Harvey and Moore) that is
> exponential so that most of the time the brane moves slowly and only
> significantly accelerates just before the collision. Therefore we
> could see that another collision would be imminent if suddenly
> constants of nature changed.
Expyrotic! Yes, most of them are ex-pyrotic now.
> To be a bit more specific, the ekpyrotic people work in the setup up
> heterotic M-Theory, that is Horava-Witten compactified on a
> Calabi-Yau. Thus, from a five dimensional point of view (small CY but
> the intervall is visible), the end-of-the-universe branes are 3-branes
> and susy implies for M5-branes to wrap a holomorphic 2-cycle in the
> CY. Hence, they are also 3-branes and they have to be at a point in
> the intervall (i.e. parallel to the extended directions of the
> end-of-the-universe branes).
Hum! Ekpyrotic is actually not Horava-Witten theory. (It seems their
propaganda was too successful.) It just looks a bit similar. Ekpyrotic
(and cyclic) requires you be able to take the interbrane distance to
infinity, or at least, to be extremely large, to get the required flat
potential. But Horava-Witten has a finite and not very large limit on
this distance because of the domain wall solution which becomes
singular at some point. (See recent work by Curio and Krause for an
update.)
People have actually done work on time-dependent solutions of real
heterotic M-theory with 5-branes, using the laboriously derived
effective supergravity: see recent work of Lukas. It is certainly not
ekpyrotic.
But your speculations also apply to this case, and in general to any
cosmology with moving branes. I suppose D-branes are easier to deal
with.
> Now, what can happen when the two types of brane meet is that the M5
> becomes an instanton in the gauge bundle of the 9-brane. However, the
> low energy physics of this is poorly understood.
So says you. This occurs in the solutions of Lukas and collaborators.
They are able to find an effective action for the instanton moduli:
http://arxiv.org/abs/http://www.arxiv.org/abs/hep-th/0312111
"We present the first examples of cosmological solutions to
four-dimensional heterotic models which include an evolving bundle
modulus. The particular bundle modulus we consider corresponds to the
width of a gauge five brane. (...) Certain properties are generic to
these solutions, regardless of initial conditions. This enables us to
make some definite statements about the dynamics subsequent to a small
instanton transition despite the fact that we cannot microscopically
describe the process itself. We also show that an effective
description of the small instanton transition by a continuous matching
of fields and their first derivatives is precluded by the form of the
respective low-energy theories before and after the transition.
So the actual moment of collision is not understood, but the aftermath
is better under control. See also http://arxiv.org/abs/http://www.arxiv.org/abs/hep-th/0309096
..
> Finally let me mention (as there was some confusion in some other post
> to this thread) that branes at angles (or curved branes) generalize
> the concept of branes vs anti-branes: Two branes correspond to two
> branes a angle and of you turn one around by 180 degrees you turn
> them into a brane anti-brane pair. So, losely speaking, any curved
> brane bears within itself a contribution from an anti-brane.
>
> Robert
Now, could this apply also to the end-of-the-world branes in M-theory?
(E.g. Fabinger-Horava.)
Robert C. Helling
Jun21-04, 05:32 AM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>On Fri, 18 Jun 2004 14:56:07 -0400, Urs Schreiber <Urs.Schreiber@uni-essen.de> wrote:\n> On Fri, 18 Jun 2004, Robert C. Helling wrote:\n>\n>> Now, the expyrotic people assume a potential for the brane position\n>> (motivated by instanton calculations a la Harvey and Moore)\n>\n>\n> Could you expand on that? What is known about this \'motivation\'? Is the\n> potential needed in order for something ekpyrotic to make sense?\n\nIn my earlier post I described the heterotic M-Theory set-up with the\nM5-branes wrapping a holomorphic 2-cycle in the CY. In fact, you can\nadd (euclidean) M2-branes to this configuration without losing all\nsusy: They have to wrap the same 2-cycle extend in the intervall\ndirection and end on the 9- and M5-branes. As all their world-volume\ndirections are space-like, they are instantons and the leading\ncontribution to the low energy theory is simply given by\nexp(-volume). As two directions are constant (the 2-cycle) the volume\nis proportional to the length of the M2-brane in the intervall\ndirection and that is given by the distance between the 9- and the\nM5-brane. At this vague order of argument this gives a potential for\nthe brane position that is -exp(-x). (I cheatet for the minus sign,\nbut there are factors anyway).\n\nAs I said, the configuration in BPS therefore some fermionic\ncontribution should cancle this force but there will still be some\neffective potential along these lines. It takes H&M 42 pages to work\nout the details in hep-th/9907026. See also the work of Lukas and\nfriends mentioned by Thomas Dent.\n\nIIRC for the ekpyrotic thing to work it required the potential to\nsuddenly go back to 0 at x=0 as otherwise there would have been far\ntoo much energy depsoited in our world but there was no explanation\nwhere this should come from.\n\n> What would the relevant time scales be? To stay in this picture: Would we\n> have time to slowly see the constants of nature varying, over, say,\n> centuries or something.\n\nDepends. It takes the M5 to travel cosmological times to travel in the\nbulk (needed for thermalization of the fluctuations) but that means\nsmall variations of constants as well.\n\n>> To be a bit more specific, the ekpyrotic people work in the setup up\n>> heterotic M-Theory,\n>\n> Oh, from what Thomas said I had gotten the impression that that scenario\n> is much more vaguely "string inspired" than this seems to suggest.\n\nOvrut is in the papers and he likes heterotic M-Theory. So a lots of\nbits of their scenario can be motivated to be generic for those kinds\nof models. Appearently, when it comes to details, this becomes\nharder. Furthermore, the three (last time i checked) versions differ\nsignificantly.\n\n\n>> Now, what can happen when the two types of brane meet is that the M5\n>> becomes an instanton in the gauge bundle of the 9-brane.\n>\n> Ok, and is this possibility taken into account in ekpyrotic models. Would\n> such models still be viable if this transformation happened?\n\nIn fact, it is a necessary ingredient: It is this instanton that\nbreaks the E8 on the visible brane to the standard model gauge group.\n\n> Since I have a license to ask stupid questions: Could you briefly explain\n> the Coulomb-branch/Higgs-branch terminiology?\n\nActually, I use this example as my aide memoire (and the title of a\nWitten paper "On the Higgs branch of..." which discusses a situation\nsimilar to the deformed case). The general nomencalture seems to be\nthat on the Coulomb branch the gauge group is broken to U(1)\'s (as the\nbranes a separated) as adjoined fields get vev\'s and on the Higgs\nbranch (bi)fundamental get masses. According to my office mate (and\nIntrilligator Seiberg), the phases are distinguisehd by the potential\nbetween two electric charges: V(r) is 1/r in the Coulomb phase,\nconstant in the Higgs phase, r in the confinig phase, 1/r log r in the\nfree electric phase and log r/r in the free magnetic phase.\n\nRobert\n\n\n--\n..oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oO o.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oO\nRobert C. Helling Department of Applied Mathematics and Theoretical Physics\nUniversity of Cambridge\nprint "Just another Phone: +44/1223/766870\nstupid .sig\\n"; http://www.aei-potsdam.mpg.de/~helling\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>On Fri, 18 Jun 2004 14:56:07 -0400, Urs Schreiber <Urs.Schreiber@uni-essen.de> wrote:
> On Fri, 18 Jun 2004, Robert C. Helling wrote:
>
>> Now, the expyrotic people assume a potential for the brane position
>> (motivated by instanton calculations a la Harvey and Moore)
>
>
> Could you expand on that? What is known about this 'motivation'? Is the
> potential needed in order for something ekpyrotic to make sense?
In my earlier post I described the heterotic M-Theory set-up with the
M5-branes wrapping a holomorphic 2-cycle in the CY. In fact, you can
add (euclidean) M2-branes to this configuration without losing all
susy: They have to wrap the same 2-cycle extend in the intervall
direction and end on the 9- and M5-branes. As all their world-volume
directions are space-like, they are instantons and the leading
contribution to the low energy theory is simply given by
\exp(-volume). As two directions are constant (the 2-cycle) the volume
is proportional to the length of the M2-brane in the intervall
direction and that is given by the distance between the 9- and the
M5-brane. At this vague order of argument this gives a potential for
the brane position that is -\exp(-x). (I cheatet for the minus sign,
but there are factors anyway).
As I said, the configuration in BPS therefore some fermionic
contribution should cancle this force but there will still be some
effective potential along these lines. It takes H&M 42 pages to work
out the details in http://www.arxiv.org/abs/hep-th/9907026. See also the work of Lukas and
friends mentioned by Thomas Dent.
IIRC for the ekpyrotic thing to work it required the potential to
suddenly go back to at x=0 as otherwise there would have been far
too much energy depsoited in our world but there was no explanation
where this should come from.
> What would the relevant time scales be? To stay in this picture: Would we
> have time to slowly see the constants of nature varying, over, say,
> centuries or something.
Depends. It takes the M5 to travel cosmological times to travel in the
bulk (needed for thermalization of the fluctuations) but that means
small variations of constants as well.
>> To be a bit more specific, the ekpyrotic people work in the setup up
>> heterotic M-Theory,
>
> Oh, from what Thomas said I had gotten the impression that that scenario
> is much more vaguely "string inspired" than this seems to suggest.
Ovrut is in the papers and he likes heterotic M-Theory. So a lots of
bits of their scenario can be motivated to be generic for those kinds
of models. Appearently, when it comes to details, this becomes
harder. Furthermore, the three (last time i checked) versions differ
significantly.
>> Now, what can happen when the two types of brane meet is that the M5
>> becomes an instanton in the gauge bundle of the 9-brane.
>
> Ok, and is this possibility taken into account in ekpyrotic models. Would
> such models still be viable if this transformation happened?
In fact, it is a necessary ingredient: It is this instanton that
breaks the E8 on the visible brane to the standard model gauge group.
> Since I have a license to ask stupid questions: Could you briefly explain
> the Coulomb-branch/Higgs-branch terminiology?
Actually, I use this example as my aide memoire (and the title of a
Witten paper "On the Higgs branch of..." which discusses a situation
similar to the deformed case). The general nomencalture seems to be
that on the Coulomb branch the gauge group is broken to U(1)'s (as the
branes a separated) as adjoined fields get vev's and on the Higgs
branch (bi)fundamental get masses. According to my office mate (and
Intrilligator Seiberg), the phases are distinguisehd by the potential
between two electric charges: V(r) is 1/r in the Coulomb phase,
constant in the Higgs phase, r in the confinig phase, 1/r log r in the
free electric phase and log r/r in the free magnetic phase.
Robert
--
..oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo. oOo.oOo.oOo.oOo.oOo.oOo.oOo.oO
Robert C. Helling Department of Applied Mathematics and Theoretical Physics
University of Cambridge
print "Just another Phone: +44/1223/766870
stupid .sig\n"; http://www.aei-potsdam.mpg.de/~helling
Robert C. Helling
Jun21-04, 05:32 AM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>On Sun, 20 Jun 2004 20:55:12 -0400, Thomas Dent <tdent@auth.gr> wrote:\n> "Robert C. Helling" <helling@ariel.physik.hu-berlin.de> wrote\n\n> Hum! Ekpyrotic is actually not Horava-Witten theory. (It seems their\n> propaganda was too successful.) It just looks a bit similar. Ekpyrotic\n> (and cyclic) requires you be able to take the interbrane distance to\n> infinity, or at least, to be extremely large, to get the required flat\n> potential. But Horava-Witten has a finite and not very large limit on\n> this distance because of the domain wall solution which becomes\n> singular at some point. (See recent work by Curio and Krause for an\n> update.)\n\nIt was definitely motivated by heterotic M-Theory and at least Ovrut\nsold it that way. And yes, because of the linear dependance of\nexp(dilaton) on the position there is a bound on the size of the\nintervall in terms of the brane tensions (that are related to Newton\'s\nconstant).\n\n> People have actually done work on time-dependent solutions of real\n> heterotic M-theory with 5-branes, using the laboriously derived\n> effective supergravity: see recent work of Lukas. It is certainly not\n> ekpyrotic.\n\nCould you expand on this? From what I see in their papers they find\nthat they cannot match the low energy degrees of freedom before and\nafter the transition but they admit they have no handle on the\ntransition itself where the M2-instantons between 9- and 5-branes\nbecome massless (tensionless strings from a 10d persepective).\n\n\n>> Now, what can happen when the two types of brane meet is that the M5\n>> becomes an instanton in the gauge bundle of the 9-brane. However, the\n>> low energy physics of this is poorly understood.\n>\n> So says you.\n\nI meant: The low energy description of the transition (due to the\ntensionless strings). Before and after the transitions more or less\nstandard LEEA methods work.\n\n\n> Now, could this apply also to the end-of-the-world branes in M-theory?\n> (E.g. Fabinger-Horava.)\n\nWhat exactly do you mean by \'this\'? I think the general theme is quite\ngeneric. You can even study mechanical models: Take N+M degrees of\nfreedom x \\in R^N and y \\in R^M and consider\n\nL= 1/2(x-dot^2+y-dot^2) - 1/2 (|x|^2 |y|^2).\n\nx are moduli before the transition and y are moduli after the\ntransition. Each set is massless as long as the the other\nvanishes. One insteresting question (warning: shameless self\nadvertisment!) is to find solutions that\ndynamically move from x=0, y=free to y=0, x=free. See for example\nhep-th/0009134 .\n\nRobert\n\n\n--\n..oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oO o.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oO\nRobert C. Helling Department of Applied Mathematics and Theoretical Physics\nUniversity of Cambridge\nprint "Just another Phone: +44/1223/766870\nstupid .sig\\n"; http://www.aei-potsdam.mpg.de/~helling\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>On Sun, 20 Jun 2004 20:55:12 -0400, Thomas Dent <tdent@auth.gr> wrote:
> "Robert C. Helling" <helling@ariel.physik.hu-berlin.de> wrote
> Hum! Ekpyrotic is actually not Horava-Witten theory. (It seems their
> propaganda was too successful.) It just looks a bit similar. Ekpyrotic
> (and cyclic) requires you be able to take the interbrane distance to
> infinity, or at least, to be extremely large, to get the required flat
> potential. But Horava-Witten has a finite and not very large limit on
> this distance because of the domain wall solution which becomes
> singular at some point. (See recent work by Curio and Krause for an
> update.)
It was definitely motivated by heterotic M-Theory and at least Ovrut
sold it that way. And yes, because of the linear dependance of
\exp(dilaton) on the position there is a bound on the size of the
intervall in terms of the brane tensions (that are related to Newton's
constant).
> People have actually done work on time-dependent solutions of real
> heterotic M-theory with 5-branes, using the laboriously derived
> effective supergravity: see recent work of Lukas. It is certainly not
> ekpyrotic.
Could you expand on this? From what I see in their papers they find
that they cannot match the low energy degrees of freedom before and
after the transition but they admit they have no handle on the
transition itself where the M2-instantons between 9- and 5-branes
become massless (tensionless strings from a 10d persepective).
>> Now, what can happen when the two types of brane meet is that the M5
>> becomes an instanton in the gauge bundle of the 9-brane. However, the
>> low energy physics of this is poorly understood.
>
> So says you.
I meant: The low energy description of the transition (due to the
tensionless strings). Before and after the transitions more or less
standard LEEA methods work.
> Now, could this apply also to the end-of-the-world branes in M-theory?
> (E.g. Fabinger-Horava.)
What exactly do you mean by 'this'? I think the general theme is quite
generic. You can even study mechanical models: Take N+M degrees of
freedom x \in R^N and y \in R^M and consider
L= 1/2(x-dot^2+y-dot^2) - 1/2 (|x|^2 |y|^2).
x are moduli before the transition and y are moduli after the
transition. Each set is massless as long as the the other
vanishes. One insteresting question (warning: shameless self
advertisment!) is to find solutions that
dynamically move from x=0, y=free to y=0, x=free. See for example
http://www.arxiv.org/abs/hep-th/0009134 .
Robert
--
..oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo. oOo.oOo.oOo.oOo.oOo.oOo.oOo.oO
Robert C. Helling Department of Applied Mathematics and Theoretical Physics
University of Cambridge
print "Just another Phone: +44/1223/766870
stupid .sig\n"; http://www.aei-potsdam.mpg.de/~helling
Thomas Dent
Jun21-04, 01:10 PM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>"Robert C. Helling" <helling@ariel.physik.hu-berlin.de> wrote\n\n> > Hum! Ekpyrotic is actually not Horava-Witten theory. (It seems their\n> > propaganda was too successful.)\n>\n> It was definitely motivated by heterotic M-Theory and at least Ovrut\n> sold it that way.\n\nYes, we all know that it was "motivated", there was a train journey\nduring which Ovrut was stuck in a carriage with Steinhardt and Turok\nand they tried to force a mating between their fields of interest. In\nthe same way as simple brane-antibrane inflation is "motivated" by the\nforce law, when actually it doesn\'t work because you can\'t just have\nthe two branes and nothing else, you have to have a compactification.\nEven though Seiberg was part of the ekpyrotic team for a while, it\ndidn\'t turn out really to be a string or M-theory model.\n\n> > People have actually done work on time-dependent solutions of real\n> > heterotic M-theory with 5-branes, using the laboriously derived\n> > effective supergravity: see recent work of Lukas. It is certainly not\n> > ekpyrotic.\n>\n> Could you expand on this?\n\nI didn\'t mean the gauge 5-brane and the moment of collision, I meant\nthe smooth cosmological evolution. See previous papers with Gray in\nwhich they look at the rolling of 5-brane moduli through the bulk and\nthe evolution of bulk moduli. In those cases they have both solutions\nwith and without collisions. Admittedly they do not include\npotentials. But the behaviour of bulk moduli should certainly be taken\ninto account. I suppose you could say it resembled ekpyrotic in that\nthere is a brane which moves and collides, but the details are rather\ndifferent.\n\n\n> > Now, could this apply also to the end-of-the-world branes in M-theory?\n> > (E.g. Fabinger-Horava.)\n>\n\nOh, "this" meant the statement that all branes are anti-branes to some\ndegree if you bend them.\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>"Robert C. Helling" <helling@ariel.physik.hu-berlin.de> wrote
> > Hum! Ekpyrotic is actually not Horava-Witten theory. (It seems their
> > propaganda was too successful.)
>
> It was definitely motivated by heterotic M-Theory and at least Ovrut
> sold it that way.
Yes, we all know that it was "motivated", there was a train journey
during which Ovrut was stuck in a carriage with Steinhardt and Turok
and they tried to force a mating between their fields of interest. In
the same way as simple brane-antibrane inflation is "motivated" by the
force law, when actually it doesn't work because you can't just have
the two branes and nothing else, you have to have a compactification.
Even though Seiberg was part of the ekpyrotic team for a while, it
didn't turn out really to be a string or M-theory model.
> > People have actually done work on time-dependent solutions of real
> > heterotic M-theory with 5-branes, using the laboriously derived
> > effective supergravity: see recent work of Lukas. It is certainly not
> > ekpyrotic.
>
> Could you expand on this?
I didn't mean the gauge 5-brane and the moment of collision, I meant
the smooth cosmological evolution. See previous papers with Gray in
which they look at the rolling of 5-brane moduli through the bulk and
the evolution of bulk moduli. In those cases they have both solutions
with and without collisions. Admittedly they do not include
potentials. But the behaviour of bulk moduli should certainly be taken
into account. I suppose you could say it resembled ekpyrotic in that
there is a brane which moves and collides, but the details are rather
different.
> > Now, could this apply also to the end-of-the-world branes in M-theory?
> > (E.g. Fabinger-Horava.)
>
Oh, "this" meant the statement that all branes are anti-branes to some
degree if you bend them.
Robert C. Helling
Jun22-04, 04:32 AM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>On Mon, 21 Jun 2004 14:10:36 -0400, Thomas Dent <tdent@auth.gr> wrote:\n\n>> > Now, could this apply also to the end-of-the-world branes in M-theory?\n>> > (E.g. Fabinger-Horava.)\n>>\n>\n> Oh, "this" meant the statement that all branes are anti-branes to some\n> degree if you bend them.\n\nHmm, how do you rotate end of the universe branes? Well, maybe one\ncould look at them as boundary conditions of open M2-branes. Then\nit might be possible to write an anti-brane as a rotated brane or some\nlimit of the gauge field (to which the M2-boundary couples).\n\nIn FH, they look at theories with different chiralities, where\nchirality is really defined using Gamma^11. But that is of course\nGamma(normal to brane) or using Hodge duality Gamma(brane volume). So,\nwhen you start rotating the brane you rotate the chirality condition\nand if you rotate by 180 degrees you changed Gamma^11 to\n-Gamma^11. There you are!\n\nRobert\n\n\n--\n..oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oO o.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oO\nRobert C. Helling Department of Applied Mathematics and Theoretical Physics\nUniversity of Cambridge\nprint "Just another Phone: +44/1223/766870\nstupid .sig\\n"; http://www.aei-potsdam.mpg.de/~helling\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>On Mon, 21 Jun 2004 14:10:36 -0400, Thomas Dent <tdent@auth.gr> wrote:
>> > Now, could this apply also to the end-of-the-world branes in M-theory?
>> > (E.g. Fabinger-Horava.)
>>
>
> Oh, "this" meant the statement that all branes are anti-branes to some
> degree if you bend them.
Hmm, how do you rotate end of the universe branes? Well, maybe one
could look at them as boundary conditions of open M2-branes. Then
it might be possible to write an anti-brane as a rotated brane or some
limit of the gauge field (to which the M2-boundary couples).
In FH, they look at theories with different chiralities, where
chirality is really defined using \Gamma^11. But that is of course
\Gamma(normal to brane) or using Hodge duality \Gamma(brane volume). So,
when you start rotating the brane you rotate the chirality condition
and if you rotate by 180 degrees you changed \Gamma^11 to
-\Gamma^11. There you are!
Robert
--
..oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo. oOo.oOo.oOo.oOo.oOo.oOo.oOo.oO
Robert C. Helling Department of Applied Mathematics and Theoretical Physics
University of Cambridge
print "Just another Phone: +44/1223/766870
stupid .sig\n"; http://www.aei-potsdam.mpg.de/~helling
Urs Schreiber
Jun22-04, 10:12 AM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>"Robert C. Helling" <helling@ariel.physik.hu-berlin.de> schrieb im\nNewsbeitrag news:2jnpmpF13mfglU1-100000@uni-berlin.de...\n> On Fri, 18 Jun 2004 14:56:07 -0400, Urs Schreiber\n<Urs.Schreiber@uni-essen.de> wrote:\n\n> IIRC for the ekpyrotic thing to work it required the potential to\n> suddenly go back to 0 at x=0 as otherwise there would have been far\n> too much energy depsoited in our world but there was no explanation\n> where this should come from.\n\nSeems to me that there are lots of big problems with the ekpyrotic model.\nWhat are the benefits of this model that justify hoping that all these\nproblems will disappear somehow? Is there anything compelling about it? I\ndon\'t mean to be critical, I am just trying to get the idea.\n\n\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>"Robert C. Helling" <helling@ariel.physik.hu-berlin.de> schrieb im
Newsbeitrag news:2jnpmpF13mfglU1-100000@uni-berlin.de...
> On Fri, 18 Jun 2004 14:56:07 -0400, Urs Schreiber
<Urs.Schreiber@uni-essen.de> wrote:
> IIRC for the ekpyrotic thing to work it required the potential to
> suddenly go back to at x=0 as otherwise there would have been far
> too much energy depsoited in our world but there was no explanation
> where this should come from.
Seems to me that there are lots of big problems with the ekpyrotic model.
What are the benefits of this model that justify hoping that all these
problems will disappear somehow? Is there anything compelling about it? I
don't mean to be critical, I am just trying to get the idea.
Urs Schreiber
Jun22-04, 11:01 AM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>"Robert C. Helling" <helling@ariel.physik.hu-berlin.de> schrieb im\nNewsbeitrag news:2jnpmpF13mfglU1-100000@uni-berlin.de...\n\n> In my earlier post I described the heterotic M-Theory set-up with the\n> M5-branes wrapping a holomorphic 2-cycle in the CY. In fact, you can\n> add (euclidean) M2-branes to this configuration without losing all\n> susy: They have to wrap the same 2-cycle extend in the intervall\n> direction and end on the 9- and M5-branes. As all their world-volume\n> directions are space-like, they are instantons and the leading\n> contribution to the low energy theory is simply given by\n> exp(-volume). As two directions are constant (the 2-cycle) the volume\n> is proportional to the length of the M2-brane in the intervall\n> direction and that is given by the distance between the 9- and the\n> M5-brane. At this vague order of argument this gives a potential for\n> the brane position that is -exp(-x). (I cheatet for the minus sign,\n> but there are factors anyway).\n\nAs far as I understand this is essentially the same (type of) effect as\nstudied in today\'s\n\nCarlos, Roberts & Schmoehe:\nMoving Five-Branes and Membrane Instantons in Low Energy Heterotic M-Theory,\nhep-th/0406171 .\n\nUnless I am confused their equation (11) gives the superpotential that you\nare talking about. In (27) they insert it into their sugra lagrangian and\ncompute the corrected (by that non-perturbative effect) EOMs in (30).\n\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>"Robert C. Helling" <helling@ariel.physik.hu-berlin.de> schrieb im
Newsbeitrag news:2jnpmpF13mfglU1-100000@uni-berlin.de...
> In my earlier post I described the heterotic M-Theory set-up with the
> M5-branes wrapping a holomorphic 2-cycle in the CY. In fact, you can
> add (euclidean) M2-branes to this configuration without losing all
> susy: They have to wrap the same 2-cycle extend in the intervall
> direction and end on the 9- and M5-branes. As all their world-volume
> directions are space-like, they are instantons and the leading
> contribution to the low energy theory is simply given by
> \exp(-volume). As two directions are constant (the 2-cycle) the volume
> is proportional to the length of the M2-brane in the intervall
> direction and that is given by the distance between the 9- and the
> M5-brane. At this vague order of argument this gives a potential for
> the brane position that is -\exp(-x). (I cheatet for the minus sign,
> but there are factors anyway).
As far as I understand this is essentially the same (type of) effect as
studied in today's
Carlos, Roberts & Schmoehe:
Moving Five-Branes and Membrane Instantons in Low Energy Heterotic M-Theory,
http://www.arxiv.org/abs/hep-th/0406171 .
Unless I am confused their equation (11) gives the superpotential that you
are talking about. In (27) they insert it into their sugra lagrangian and
compute the corrected (by that non-perturbative effect) EOMs in (30).
Urs Schreiber
Jun22-04, 11:01 AM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>"Robert C. Helling" <helling@ariel.physik.hu-berlin.de> schrieb im\nNewsbeitrag news:2jnpmpF13mfglU1-100000@uni-berlin.de...\n\n> In my earlier post I described the heterotic M-Theory set-up with the\n> M5-branes wrapping a holomorphic 2-cycle in the CY. In fact, you can\n> add (euclidean) M2-branes to this configuration without losing all\n> susy: They have to wrap the same 2-cycle extend in the intervall\n> direction and end on the 9- and M5-branes. As all their world-volume\n> directions are space-like, they are instantons and the leading\n> contribution to the low energy theory is simply given by\n> exp(-volume). As two directions are constant (the 2-cycle) the volume\n> is proportional to the length of the M2-brane in the intervall\n> direction and that is given by the distance between the 9- and the\n> M5-brane. At this vague order of argument this gives a potential for\n> the brane position that is -exp(-x). (I cheatet for the minus sign,\n> but there are factors anyway).\n\nAs far as I understand this is essentially the same (type of) effect as\nstudied in today\'s\n\nCarlos, Roberts & Schmoehe:\nMoving Five-Branes and Membrane Instantons in Low Energy Heterotic M-Theory,\nhep-th/0406171 .\n\nUnless I am confused their equation (11) gives the superpotential that you\nare talking about. In (27) they insert it into their sugra lagrangian and\ncompute the corrected (by that non-perturbative effect) EOMs in (30).\n\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>"Robert C. Helling" <helling@ariel.physik.hu-berlin.de> schrieb im
Newsbeitrag news:2jnpmpF13mfglU1-100000@uni-berlin.de...
> In my earlier post I described the heterotic M-Theory set-up with the
> M5-branes wrapping a holomorphic 2-cycle in the CY. In fact, you can
> add (euclidean) M2-branes to this configuration without losing all
> susy: They have to wrap the same 2-cycle extend in the intervall
> direction and end on the 9- and M5-branes. As all their world-volume
> directions are space-like, they are instantons and the leading
> contribution to the low energy theory is simply given by
> \exp(-volume). As two directions are constant (the 2-cycle) the volume
> is proportional to the length of the M2-brane in the intervall
> direction and that is given by the distance between the 9- and the
> M5-brane. At this vague order of argument this gives a potential for
> the brane position that is -\exp(-x). (I cheatet for the minus sign,
> but there are factors anyway).
As far as I understand this is essentially the same (type of) effect as
studied in today's
Carlos, Roberts & Schmoehe:
Moving Five-Branes and Membrane Instantons in Low Energy Heterotic M-Theory,
http://www.arxiv.org/abs/hep-th/0406171 .
Unless I am confused their equation (11) gives the superpotential that you
are talking about. In (27) they insert it into their sugra lagrangian and
compute the corrected (by that non-perturbative effect) EOMs in (30).
Robert C. Helling
Jun23-04, 03:41 AM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>On Tue, 22 Jun 2004 12:01:56 -0400, Urs Schreiber <Urs.Schreiber@uni-essen.de> wrote:\n>\n> As far as I understand this is essentially the same (type of) effect as\n> studied in today\'s\n>\n> Carlos, Roberts & Schmoehe:\n> Moving Five-Branes and Membrane Instantons in Low Energy Heterotic M-Theory,\n> hep-th/0406171 .\n\nIndeed. The paper I was talking about is their [27]. And of course in\nrealistic models there are more moduli and their action depends on\ngeometric details of the CY.\n\nRobert\n\n\n--\n..oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oO o.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oO\nRobert C. Helling Department of Applied Mathematics and Theoretical Physics\nUniversity of Cambridge\nprint "Just another Phone: +44/1223/766870\nstupid .sig\\n"; http://www.aei-potsdam.mpg.de/~helling\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>On Tue, 22 Jun 2004 12:01:56 -0400, Urs Schreiber <Urs.Schreiber@uni-essen.de> wrote:
>
> As far as I understand this is essentially the same (type of) effect as
> studied in today's
>
> Carlos, Roberts & Schmoehe:
> Moving Five-Branes and Membrane Instantons in Low Energy Heterotic M-Theory,
> http://www.arxiv.org/abs/hep-th/0406171 .
Indeed. The paper I was talking about is their [27]. And of course in
realistic models there are more moduli and their action depends on
geometric details of the CY.
Robert
--
..oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo. oOo.oOo.oOo.oOo.oOo.oOo.oOo.oO
Robert C. Helling Department of Applied Mathematics and Theoretical Physics
University of Cambridge
print "Just another Phone: +44/1223/766870
stupid .sig\n"; http://www.aei-potsdam.mpg.de/~helling
Robert C. Helling
Jun23-04, 03:41 AM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>On Tue, 22 Jun 2004 11:12:22 -0400, Urs Schreiber <Urs.Schreiber@uni-essen.de> wrote:\n> "Robert C. Helling" <helling@ariel.physik.hu-berlin.de> schrieb im\n> Newsbeitrag news:2jnpmpF13mfglU1-100000@uni-berlin.de...\n>> On Fri, 18 Jun 2004 14:56:07 -0400, Urs Schreiber\n><Urs.Schreiber@uni-essen.de> wrote:\n\n> Seems to me that there are lots of big problems with the ekpyrotic model.\n> What are the benefits of this model that justify hoping that all these\n> problems will disappear somehow? Is there anything compelling about it?\n\nI think in general I agree with your assessment. And we haven\'t even\ntalked about the "nearly BPS" assumptions...\n\nHowever, I like the idea of trying to do cosmology with the objects\nyou find in string theory rather than using ad hoc fields with very\nspecial potentials.\n\nRobert\n\n--\n..oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oO o.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oO\nRobert C. Helling Department of Applied Mathematics and Theoretical Physics\nUniversity of Cambridge\nprint "Just another Phone: +44/1223/766870\nstupid .sig\\n"; http://www.aei-potsdam.mpg.de/~helling\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>On Tue, 22 Jun 2004 11:12:22 -0400, Urs Schreiber <Urs.Schreiber@uni-essen.de> wrote:
> "Robert C. Helling" <helling@ariel.physik.hu-berlin.de> schrieb im
> Newsbeitrag news:2jnpmpF13mfglU1-100000@uni-berlin.de...
>> On Fri, 18 Jun 2004 14:56:07 -0400, Urs Schreiber
><Urs.Schreiber@uni-essen.de> wrote:
> Seems to me that there are lots of big problems with the ekpyrotic model.
> What are the benefits of this model that justify hoping that all these
> problems will disappear somehow? Is there anything compelling about it?
I think in general I agree with your assessment. And we haven't even
talked about the "nearly BPS" assumptions...
However, I like the idea of trying to do cosmology with the objects
you find in string theory rather than using ad hoc fields with very
special potentials.
Robert
--
..oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo. oOo.oOo.oOo.oOo.oOo.oOo.oOo.oO
Robert C. Helling Department of Applied Mathematics and Theoretical Physics
University of Cambridge
print "Just another Phone: +44/1223/766870
stupid .sig\n"; http://www.aei-potsdam.mpg.de/~helling
Urs Schreiber
Jun23-04, 04:12 AM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>On Wed, 23 Jun 2004, Robert C. Helling wrote:\n\n> On Tue, 22 Jun 2004 12:01:56 -0400, Urs Schreiber <Urs.Schreiber@uni-essen.de> wrote:\n> >\n> > As far as I understand this is essentially the same (type of) effect as\n> > studied in today\'s\n> >\n> > Carlos, Roberts & Schmoehe:\n> > Moving Five-Branes and Membrane Instantons in Low Energy Heterotic M-Theory,\n> > hep-th/0406171 .\n>\n> Indeed. The paper I was talking about is their [27]. And of course in\n> realistic models there are more moduli and their action depends on\n> geometric details of the CY.\n\nOk. Sorry, I had not looked at the papers that you were referring\nto before.\n\nWhat I would like to better understand, conceptually, since it also seems\nto play a role in KKLT-like considerations concerning the \'landscape\', are\nsentences of the type as in the very last paragraph on p.3 of that paper\nhep-th/0406171:\n\n"There are a number of non-perturbative effects we could consider, each\ncontributing to the superpotential for the chiral superfields."\n\nThe M2-brane instantons that you mentioned are one example and it is the\none chosen for further considerations by these authors. Further\nnon-perturbative effects are mentioned in that paragraph, e.g.\n\n- gaugino condensation (in which sense is that non-perturbative? Is it\nsimilar to how tachyon-condensation is \'non-perturbative\' the way we\ndiscussed here:\nhttp://groups.google.de/groups?selm=Pine.LNX.4.31.0406031119090.16251-100000%40feynman.harvard.edu,\nnamely that the position of the vev in the condensate scales with 1/g?)\n\n- wrappend M5 branes .\n\nWhat is the systematics that is involved here? Should one in principle\ninclude all these non-perturbative effects in the effective action (e.g.\nin equation (27)) or can there be reasons to ignore some?\n\nMore generally, how many such effects could there possibly be, and how\ndoes one know that one has found some/most/all of them?\n\nIf we knew all of these effects (apparently we don\'t), and included all of\nthem in the effective action, would that amount to having a full\nnon-perturbative definition of string theory?\n\n(Sorry if these questions are elementary and maybe confused, but I am\nlacking some conceptual understanding here. I vaguely tried to address\nthat before:\nhttp://golem.ph.utexas.edu/~distler/blog/archives/000371.html#c001171)\n\n\nAnother question: In their example on p. 8 the above authors discuss some\naspects of solutions of the equations of motion they obtained. In\nparticular the time dependence of the CY plays an central role.\n\nDo you know if there have been any attempts to combine brane\ncosmology with the very interesting results concerning time-dependent CYs\nand csomological flop-transitions produced by Thomas Mohaupt and his\ngroup, as in e.g. hep-th/0311016 hep-th/0312195?\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>On Wed, 23 Jun 2004, Robert C. Helling wrote:
> On Tue, 22 Jun 2004 12:01:56 -0400, Urs Schreiber <Urs.Schreiber@uni-essen.de> wrote:
> >
> > As far as I understand this is essentially the same (type of) effect as
> > studied in today's
> >
> > Carlos, Roberts & Schmoehe:
> > Moving Five-Branes and Membrane Instantons in Low Energy Heterotic M-Theory,
> > http://www.arxiv.org/abs/hep-th/0406171 .
>
> Indeed. The paper I was talking about is their [27]. And of course in
> realistic models there are more moduli and their action depends on
> geometric details of the CY.
Ok. Sorry, I had not looked at the papers that you were referring
to before.
What I would like to better understand, conceptually, since it also seems
to play a role in KKLT-like considerations concerning the 'landscape', are
sentences of the type as in the very last paragraph on p.3 of that paper
http://www.arxiv.org/abs/hep-th/0406171:
"There are a number of non-perturbative effects we could consider, each
contributing to the superpotential for the chiral superfields."
The M2-brane instantons that you mentioned are one example and it is the
one chosen for further considerations by these authors. Further
non-perturbative effects are mentioned in that paragraph, e.g.
- gaugino condensation (in which sense is that non-perturbative? Is it
similar to how tachyon-condensation is 'non-perturbative' the way we
discussed here:
http://groups.google.de/groups?selm=Pine.LNX.4.31.0406031119090.16251-100000%40feynman.harvard.edu,
namely that the position of the vev in the condensate scales with 1/g?)
- wrappend M5 branes .
What is the systematics that is involved here? Should one in principle
include all these non-perturbative effects in the effective action (e.g.
in equation (27)) or can there be reasons to ignore some?
More generally, how many such effects could there possibly be, and how
does one know that one has found some/most/all of them?
If we knew all of these effects (apparently we don't), and included all of
them in the effective action, would that amount to having a full
non-perturbative definition of string theory?
(Sorry if these questions are elementary and maybe confused, but I am
lacking some conceptual understanding here. I vaguely tried to address
that before:
http://golem.ph.utexas.edu/~distler/blog/archives/000371.html#c001171)
Another question: In their example on p. 8 the above authors discuss some
aspects of solutions of the equations of motion they obtained. In
particular the time dependence of the CY plays an central role.
Do you know if there have been any attempts to combine brane
cosmology with the very interesting results concerning time-dependent CYs
and csomological flop-transitions produced by Thomas Mohaupt and his
group, as in e.g. http://www.arxiv.org/abs/hep-th/0311016 http://www.arxiv.org/abs/hep-th/0312195?
Robert C. Helling
Jun24-04, 05:57 AM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>On Wed, 23 Jun 2004 05:12:18 -0400, Urs Schreiber <Urs.Schreiber@uni-essen.de> wrote:\n\n> What is the systematics that is involved here? Should one in principle\n> include all these non-perturbative effects in the effective action (e.g.\n> in equation (27)) or can there be reasons to ignore some?\n>\n> More generally, how many such effects could there possibly be, and how\n> does one know that one has found some/most/all of them?\n\nIn the end, you have to calculate the contribution but very often you\ncan interpret the effect as one object wrapping cycles in the geometry\n(at least in the geometric, large volume limit). I don\'t have a good\nintuition regarding gluino condensates but it seems a generic\nbehaviour for theories with at most N=1 susy to break the gauge group\nto its centre.\n\n> If we knew all of these effects (apparently we don\'t), and included all of\n> them in the effective action, would that amount to having a full\n> non-perturbative definition of string theory?\n\nYou can define what ever you want ;-) .\n\nWhat are your criteria? Define a theory non-perturbatively and then\ncheck that it coincides with string theory in the perturbative regime(s)\nplus existence of BPS objects?\n\nFurthermore, you are probably talking about the low energy effective\naction (containing only massless or light fields). That approximation\nis not likely to be meaningful for example in strongly curved\nbackgrounds. Unfortunately, those are also the ones where the\nnon-perturbative effects (e.g. worldsheet instantons) become important\nand the geometric picture (manifolds, submanifolds wrapping cycles\netc) breaks down. You can see this for situations where at least you\nhave the CFT under control. For example Jecques and friends found\nD-brane mododromies: You can start with say a Dp-brane in the\ngeometric regime than make an (adiabatic) circle in the (Kaehler)\nmoduli space and come back with a D(p\')-brane without noticing\nsomething radical (like a phase transition) happened midway. This\nteaches you that beyond large volumes not even dimensions have a good\nmeaning. This should illustrate, that in those situations you should\nbe careful applying geometric intuition of instantons corresponding\nbranes wrapping cycles.\n\n> Do you know if there have been any attempts to combine brane\n> cosmology with the very interesting results concerning time-dependent CYs\n> and csomological flop-transitions produced by Thomas Mohaupt and his\n> group, as in e.g. hep-th/0311016 hep-th/0312195?\n\nI thought Thomas\' motivation for this was cosmological. At least that\nis the way he presents this work at conferences.\n\nRobert\n--\n..oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oO o.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oO\nRobert C. Helling Department of Applied Mathematics and Theoretical Physics\nUniversity of Cambridge\nprint "Just another Phone: +44/1223/766870\nstupid .sig\\n"; http://www.aei-potsdam.mpg.de/~helling\n\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>On Wed, 23 Jun 2004 05:12:18 -0400, Urs Schreiber <Urs.Schreiber@uni-essen.de> wrote:
> What is the systematics that is involved here? Should one in principle
> include all these non-perturbative effects in the effective action (e.g.
> in equation (27)) or can there be reasons to ignore some?
>
> More generally, how many such effects could there possibly be, and how
> does one know that one has found some/most/all of them?
In the end, you have to calculate the contribution but very often you
can interpret the effect as one object wrapping cycles in the geometry
(at least in the geometric, large volume limit). I don't have a good
intuition regarding gluino condensates but it seems a generic
behaviour for theories with at most N=1 susy to break the gauge group
to its centre.
> If we knew all of these effects (apparently we don't), and included all of
> them in the effective action, would that amount to having a full
> non-perturbative definition of string theory?
You can define what ever you want ;-) .
What are your criteria? Define a theory non-perturbatively and then
check that it coincides with string theory in the perturbative regime(s)
plus existence of BPS objects?
Furthermore, you are probably talking about the low energy effective
action (containing only massless or light fields). That approximation
is not likely to be meaningful for example in strongly curved
backgrounds. Unfortunately, those are also the ones where the
non-perturbative effects (e.g. worldsheet instantons) become important
and the geometric picture (manifolds, submanifolds wrapping cycles
etc) breaks down. You can see this for situations where at least you
have the CFT under control. For example Jecques and friends found
D-brane mododromies: You can start with say a Dp-brane in the
geometric regime than make an (adiabatic) circle in the (Kaehler)
moduli space and come back with a D(p')-brane without noticing
something radical (like a phase transition) happened midway. This
teaches you that beyond large volumes not even dimensions have a good
meaning. This should illustrate, that in those situations you should
be careful applying geometric intuition of instantons corresponding
branes wrapping cycles.
> Do you know if there have been any attempts to combine brane
> cosmology with the very interesting results concerning time-dependent CYs
> and csomological flop-transitions produced by Thomas Mohaupt and his
> group, as in e.g. http://www.arxiv.org/abs/hep-th/0311016 http://www.arxiv.org/abs/hep-th/0312195?
I thought Thomas' motivation for this was cosmological. At least that
is the way he presents this work at conferences.
Robert
--
..oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo. oOo.oOo.oOo.oOo.oOo.oOo.oOo.oO
Robert C. Helling Department of Applied Mathematics and Theoretical Physics
University of Cambridge
print "Just another Phone: +44/1223/766870
stupid .sig\n"; http://www.aei-potsdam.mpg.de/~helling
Thomas Dent
Jun24-04, 07:52 AM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>Urs Schreiber <Urs.Schreiber@uni-essen.de> wrote\n\n> > Indeed. The paper I was talking about is their [27]. And of course in\n> > realistic models there are more moduli and their action depends on\n> > geometric details of the CY.\n>\n> sentences of the type as in the very last paragraph on p.3 of that paper\n> hep-th/0406171:\n>\n> "There are a number of non-perturbative effects we could consider, each\n> contributing to the superpotential for the chiral superfields."\n>\n> The M2-brane instantons that you mentioned are one example and it is the\n> one chosen for further considerations by these authors. Further\n> non-perturbative effects are mentioned in that paragraph, e.g.\n>\n> - gaugino condensation (in which sense is that non-perturbative? Is it\n> similar to how tachyon-condensation is \'non-perturbative\' the way we\n> discussed here:\n> http://groups.google.de/groups?selm=Pine.LNX.4.31.0406031119090.16251-100000%40feynman.harvard.edu,\n> namely that the position of the vev in the condensate scales with 1/g?)\n\nGaugino condensation is a strong coupling effect in gauge theory which\ngoes as e^(-beta/g^2), like the QCD scale, which arguably is the\noriginal definition of what a nonperturbative effect is! Now, there\nwere always people (Shenker, Banks/Dine) speculating that there would\nalso be an effect with e^{-k/g}, which could stabilize the dilaton,\nwhich would come from strongly coupled string.\n\n> - wrapped M5 branes .\n>\n> What is the systematics that is involved here? Should one in principle\n> include all these non-perturbative effects in the effective action (e.g.\n> in equation (27)) or can there be reasons to ignore some?\n\nIn het. M-theory there is a series of papers by Ovrut and\ncollaborators which very laboriously goes and calculates all of them\n(membrane instantons for different types of brane in different\ngeometrical configurations), finding that they depend on various\nparameters and may be zero or not as the case may be, and have\nparticular dependences on the moduli. If you can understand them, then\ngaugino condensation is absolutely easy!\n\n> More generally, how many such effects could there possibly be, and how\n> does one know that one has found some/most/all of them?\n\nI think Ovrut et al. do think they know all of them, at least in some\napproximation.\n\n> If we knew all of these effects (apparently we don\'t), and included all of\n> them in the effective action, would that amount to having a full\n> non-perturbative definition of string theory?\n\nNo, only a knowledge of what happens around certain corners close to\nD=11 SUGRA on S1/Z2. One point is that these effects generically break\nSUSY completely and introduce a cosmo. constant, hence there is a\nbackreaction which makes the original calculation (based on flat 4d\nspace) inexact, i.e. in practice, valid in regions of parameter space\nwhere the instantons are much smaller than 1. And besides, het\nM-theory is not an exact solution.\n\nThe claim is that these membrane instantons *do* give the correct\ncorrections to weakly-coupled heterotic string in the case where g is\nnot infinitesimally small.\n\n\n> Another question: In their example on p. 8 the above authors discuss some\n> aspects of solutions of the equations of motion they obtained. In\n> particular the time dependence of the CY plays an central role.\n>\n> Do you know if there have been any attempts to combine brane\n> cosmology with the very interesting results concerning time-dependent CYs\n> and csomological flop-transitions produced by Thomas Mohaupt and his\n> group, as in e.g. hep-th/0311016 hep-th/0312195?\n\nBrandle and Lukas is the only one I know in het M-theory, the Stanford\npeople have done something similar with points of enhanced symmetry\n(Linde, Kachru and a load of other authors).\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>Urs Schreiber <Urs.Schreiber@uni-essen.de> wrote
> > Indeed. The paper I was talking about is their [27]. And of course in
> > realistic models there are more moduli and their action depends on
> > geometric details of the CY.
>
> sentences of the type as in the very last paragraph on p.3 of that paper
> http://www.arxiv.org/abs/hep-th/0406171:
>
> "There are a number of non-perturbative effects we could consider, each
> contributing to the superpotential for the chiral superfields."
>
> The M2-brane instantons that you mentioned are one example and it is the
> one chosen for further considerations by these authors. Further
> non-perturbative effects are mentioned in that paragraph, e.g.
>
> - gaugino condensation (in which sense is that non-perturbative? Is it
> similar to how tachyon-condensation is 'non-perturbative' the way we
> discussed here:
> http://groups.google.de/groups?selm=Pine.LNX.4.31.0406031119090.16251-100000%40feynman.harvard.edu,
> namely that the position of the vev in the condensate scales with 1/g?)
Gaugino condensation is a strong coupling effect in gauge theory which
goes as e^(-\beta/g^2), like the QCD scale, which arguably is the
original definition of what a nonperturbative effect is! Now, there
were always people (Shenker, Banks/Dine) speculating that there would
also be an effect with e^{-k/g}, which could stabilize the dilaton,
which would come from strongly coupled string.
> - wrapped M5 branes .
>
> What is the systematics that is involved here? Should one in principle
> include all these non-perturbative effects in the effective action (e.g.
> in equation (27)) or can there be reasons to ignore some?
In het. M-theory there is a series of papers by Ovrut and
collaborators which very laboriously goes and calculates all of them
(membrane instantons for different types of brane in different
geometrical configurations), finding that they depend on various
parameters and may be zero or not as the case may be, and have
particular dependences on the moduli. If you can understand them, then
gaugino condensation is absolutely easy!
> More generally, how many such effects could there possibly be, and how
> does one know that one has found some/most/all of them?
I think Ovrut et al. do think they know all of them, at least in some
approximation.
> If we knew all of these effects (apparently we don't), and included all of
> them in the effective action, would that amount to having a full
> non-perturbative definition of string theory?
No, only a knowledge of what happens around certain corners close to
D=11 SUGRA on S1/Z2. One point is that these effects generically break
SUSY completely and introduce a cosmo. constant, hence there is a
backreaction which makes the original calculation (based on flat 4d
space) inexact, i.e. in practice, valid in regions of parameter space
where the instantons are much smaller than 1. And besides, het
M-theory is not an exact solution.
The claim is that these membrane instantons *do* give the correct
corrections to weakly-coupled heterotic string in the case where g is
not infinitesimally small.
> Another question: In their example on p. 8 the above authors discuss some
> aspects of solutions of the equations of motion they obtained. In
> particular the time dependence of the CY plays an central role.
>
> Do you know if there have been any attempts to combine brane
> cosmology with the very interesting results concerning time-dependent CYs
> and csomological flop-transitions produced by Thomas Mohaupt and his
> group, as in e.g. http://www.arxiv.org/abs/hep-th/0311016 http://www.arxiv.org/abs/hep-th/0312195?
Brandle and Lukas is the only one I know in het M-theory, the Stanford
people have done something similar with points of enhanced symmetry
(Linde, Kachru and a load of other authors).
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