Question about the future of string theory

Pam Crouch

<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>I\'m curious; assuming string theory can be reconciled with existing physics\ntheories, what could cause it to be discarded in the future?\n\nIn other words, how could string theory be disproven (if it\'s not to be\nrepresentative of reality)?\n\n--Pam\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>I'm curious; assuming string theory can be reconciled with existing physics
theories, what could cause it to be discarded in the future?

In other words, how could string theory be disproven (if it's not to be
representative of reality)?

--Pam

Ulmo

<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>Pam Crouch <jasonpam@nospammingswbell.net> wrote in message news:<QTBIc.14797\\$EN.2638-100000@newssvr24.news.prodigy.com>...\n\n> I\'m curious; assuming string theory can be reconciled with existing physics\n> theories,\n\nWhat do you mean "reconciled"? All theories are an extension of\nprevious theories. There has never been anything in string theory that\nis inconsistent with observation.\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>Pam Crouch <jasonpam@nospammingswbell.net> wrote in message news:<QTBIc.14797$EN.2638-100000@new...rodigy.com>...

> I'm curious; assuming string theory can be reconciled with existing physics
> theories,

What do you mean "reconciled"? All theories are an extension of
previous theories. There has never been anything in string theory that
is inconsistent with observation.

Lubos Motl

<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, 12 Jul 2004, Pam Crouch wrote:\n\n> I\'m curious; assuming string theory can be reconciled with existing physics\n> theories, what could cause it to be discarded in the future?\n\nThere are various such possibilities. One possibility is that the\nhumankind will give up any further progress in theoretical particle\nphysics. In this case, people will stop working on string theory as well\nas everything else.\n\nThe other possibility how to discard string theory is if someone finds\nanother underlying theory that will look more convincing, attractive,\nrealistic, and/or deep and beautiful than string theory. In that case,\npeople would jump on this other theory. Well, today it looks unlikely.\nThere is no other (known) deeper theory besides string theory that would\nreproduce quantum field theory and general relativity.\n\n> In other words, how could string theory be disproven (if it\'s not to be\n> representative of reality)?\n\nIf you really want to disprove string theory, you would have to find a\nprocess in the world and you would have to be able to argue that it could\nnot happen according to anything in string theory. Yes, this possibility\nseems to be very far because string theory agrees with reality using the\nresolution how well we understand the theory today.\n_______________________________________________________________ _______________\nE-mail: lumo@matfyz.cz fax: +1-617/496-0110 Web: http://lumo.matfyz.cz/\neFax: +1-801/454-1858 work: +1-617/496-8199 home: +1-617/868-4487 (call)\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 Mon, 12 Jul 2004, Pam Crouch wrote:

> I'm curious; assuming string theory can be reconciled with existing physics
> theories, what could cause it to be discarded in the future?

There are various such possibilities. One possibility is that the
humankind will give up any further progress in theoretical particle
physics. In this case, people will stop working on string theory as well
as everything else.

The other possibility how to discard string theory is if someone finds
another underlying theory that will look more convincing, attractive,
realistic, [itex]and/or[/itex] deep and beautiful than string theory. In that case,
people would jump on this other theory. Well, today it looks unlikely.
There is no other (known) deeper theory besides string theory that would
reproduce quantum field theory and general relativity.

> In other words, how could string theory be disproven (if it's not to be
> representative of reality)?

If you really want to disprove string theory, you would have to find a
process in the world and you would have to be able to argue that it could
not happen according to anything in string theory. Yes, this possibility
seems to be very far because string theory agrees with reality using the
resolution how well we understand the theory today.
__{____________________________________________________________________ ________}
E-mail: lumo@matfyz.cz fax: [itex]+1-617/496-0110[/itex] Web: http://lumo.matfyz.cz/
eFax: [itex]+1-801/454-1858[/itex] work: [itex]+1-617/496-8199[/itex] home: [itex]+1-617/868-4487[/itex] (call)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^

Lubos Motl

<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, 19 Jul 2004, DickT wrote:\n\n> Lubos, just to consider one scenario I have seen mentioned, some\n> people think supersymmetry can be falsified by TEV level observations.\n> Just suppose that were to happen, what would be the impact on string\n> physics?\n\nGood question. First of all, the LHC-scale supersymmetry is natural, but\nit is not strictly speaking inevitable. One of the reasons we like\nsupersymmetry is that it explains the hierarchy problem - more precisely,\nit explains why the huge gap between the Higgs mass (the electroweak\nscale) on one side and the Planck (or GUT) scale on the other side is\nprotected against quantum corrections.\n\nThe natural value of the Higgs mass is comparable to the mass of the\nsuperpartners predicted by SUSY, but there is no definitive reason not to\nhave a little bit less natural relation - i.e. heavier superpartners. In\nother words, Nature can still be tuned a bit - instead of being heavily\nfine-tuned. Already today we know that it must be tuned on a 1% level,\nwhatever is the quantitative method that obtained this number.\n\nAt any rate, the absence of any signs of supersymmetry at the LHC will\nreduce the interests of the physics community about supersymmetry, despite\nthe possibility that SUSY can still be higher in energy. String theory is\ncorrelated with SUSY, so such a negative result will be negative news for\nstring theory, too. But SUSY and string theory are not the same thing, and\nthey are independent to some extent.\n\nNevertheless it is still possible that\n\n1. either supersymmetry needs higher energies still\n2. the world is described by a non-supersymmetric string theory, or string\ntheory with SUSY broken at extremely high scales so that it is effectively\nnonsupersymmetric\n\nAll such possibilities are there and each of them has a certain\nprobability in our scheme of the things.\n\nThe precise development of power in theoretical particle physics will\ndepend on the precise thing that *will* be discovered by the LHC. If the\nLHC discovers a single Higgs and nothing else - i.e. the minimal Standard\nModel - and I personally find this option ugly but totally plausible - it\nwill be a triumph for the Standard Model and it will extrapolate its\nvalidity much further than we thought, but it will definitely be bad news\nfor the whole future of particle physics because even with 1.5 billion\ndollars we won\'t have any new data compared to today. We won\'t move\nforward and we won\'t solve the things that we call "problems" of the\nStandard Model - on the contrary, we will have a tendency to convince\nourselves that they are not really problems.\n\nIf the LHC discovers something else and nonstringy - substructure of\nquarks (preons), substructure of Higgs (technicolor), new gauge symmetries\nin general, or something along those lines, more people will jump from\nstringy-inspired subjects on these phenomenological models and the\ntheoretical string theory will suffer, too.\n\nOn the other hand, the LHC can also discover new material supporting\nstring theory that is unrelated to supersymmetry - namely excited string\nstates; small black holes; Kaluza-Klein modes (particles moving in extra\ndimensions), and so on. Even if the stringy realization of such models\nwill not be known immediately, such discoveries could be a bigger triumph\nfor string theory than the discovery of supersymmetry.\n\n_____________________________________________________ _________________________\nE-mail: lumo@matfyz.cz fax: +1-617/496-0110 Web: http://lumo.matfyz.cz/\neFax: +1-801/454-1858 work: +1-617/496-8199 home: +1-617/868-4487 (call)\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 Mon, 19 Jul 2004, DickT wrote:

> Lubos, just to consider one scenario I have seen mentioned, some
> people think supersymmetry can be falsified by TEV level observations.
> Just suppose that were to happen, what would be the impact on string
> physics?

Good question. First of all, the LHC-scale supersymmetry is natural, but
it is not strictly speaking inevitable. One of the reasons we like
supersymmetry is that it explains the hierarchy problem - more precisely,
it explains why the huge gap between the Higgs mass (the electroweak
scale) on one side and the Planck (or GUT) scale on the other side is
protected against quantum corrections.

The natural value of the Higgs mass is comparable to the mass of the
superpartners predicted by SUSY, but there is no definitive reason not to
have a little bit less natural relation - i.e. heavier superpartners. In
other words, Nature can still be tuned a bit - instead of being heavily
fine-tuned. Already today we know that it must be tuned on a 1% level,
whatever is the quantitative method that obtained this number.

At any rate, the absence of any signs of supersymmetry at the LHC will
reduce the interests of the physics community about supersymmetry, despite
the possibility that SUSY can still be higher in energy. String theory is
correlated with SUSY, so such a negative result will be negative news for
string theory, too. But SUSY and string theory are not the same thing, and
they are independent to some extent.

Nevertheless it is still possible that

1. either supersymmetry needs higher energies still
2. the world is described by a non-supersymmetric string theory, or string
theory with SUSY broken at extremely high scales so that it is effectively
nonsupersymmetric

All such possibilities are there and each of them has a certain
probability in our scheme of the things.

The precise development of power in theoretical particle physics will
depend on the precise thing that *will* be discovered by the LHC. If the
LHC discovers a single Higgs and nothing else - i.e. the minimal Standard
Model - and I personally find this option ugly but totally plausible [itex]- it[/itex]
will be a triumph for the Standard Model and it will extrapolate its
validity much further than we thought, but it will definitely be bad news
for the whole future of particle physics because even with 1.5 billion
dollars we won't have any new data compared to today[itex]. We[/itex] won't move
forward and we won't solve the things that we call "problems" of the
Standard Model - on the contrary, we will have a tendency to convince
ourselves that they are not really problems.

If the LHC discovers something else and nonstringy - substructure of
quarks (preons), substructure of Higgs (technicolor), new gauge symmetries
in general, or something along those lines, more people will jump from
stringy-inspired subjects on these phenomenological models and the
theoretical string theory will suffer, too.

On the other hand, the LHC can also discover new material supporting
string theory that is unrelated to supersymmetry - namely excited string
states; small black holes; Kaluza-Klein modes (particles moving in extra
dimensions), and so on. Even if the stringy realization of such models
will not be known immediately, such discoveries could be a bigger triumph
for string theory than the discovery of supersymmetry.

__{____________________________________________________________________ ________}
E-mail: lumo@matfyz.cz fax: [itex]+1-617/496-0110[/itex] Web: http://lumo.matfyz.cz/
eFax: [itex]+1-801/454-1858[/itex] work: [itex]+1-617/496-8199[/itex] home: [itex]+1-617/868-4487[/itex] (call)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^

DickT

<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>Lubos Motl <motl@feynman.harvard.edu> wrote in message news:<Pine.LNX.4.31.0407180133570.17874-100000@einstein.physics.harvard.edu>...\n\n> ...\n> If you really want to disprove string theory, you would have to find a\n> process in the world and you would have to be able to argue that it could\n> not happen according to anything in string theory. Yes, this possibility\n> ...\n\nLubos, just to consider one scenario I have seen mentioned, some\npeople think supersymmetry can be falsified by TEV level observations.\nJust suppose that were to happen, what would be the impact on string\nphysics?\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>Lubos Motl <motl@feynman.harvard.edu> wrote in message news:<Pine.LNX.4.31.0407180133570.17...arvard.edu>...

> ...
> If you really want to disprove string theory, you would have to find a
> process in the world and you would have to be able to argue that it could
> not happen according to anything in string theory. Yes, this possibility
> ...

Lubos, just to consider one scenario I have seen mentioned, some
people think supersymmetry can be falsified by TEV level observations.
Just suppose that were to happen, what would be the impact on string
physics?

Creighton Hogg

<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>\n\nOn Mon, 19 Jul 2004, Lubos Motl wrote:\n\n[...]\n\n> On the other hand, the LHC can also discover new material supporting\n> string theory that is unrelated to supersymmetry - namely excited string\n> states; small black holes; Kaluza-Klein modes (particles moving in extra\n> dimensions), and so on. Even if the stringy realization of such models\n> will not be known immediately, such discoveries could be a bigger triumph\n> for string theory than the discovery of supersymmetry.\n\nHi Dr. Motl,\nHow readily testable are predictions like the Kaluza-Klein modes? Have\npeople worked out the cross-section for production and looked at how the\nsignal would look in the LHC? What about the excited string states? I\'m\nnot really sure if I even understand what you mean by that.\n\n[Moderator\'s note: Quoted text trimmed to a reasonable amount by\nmoderator. -usc]\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, 19 Jul 2004, Lubos Motl wrote:

[...]

> On the other hand, the LHC can also discover new material supporting
> string theory that is unrelated to supersymmetry - namely excited string
> states; small black holes; Kaluza-Klein modes (particles moving in extra
> dimensions), and so on. Even if the stringy realization of such models
> will not be known immediately, such discoveries could be a bigger triumph
> for string theory than the discovery of supersymmetry.

Hi Dr. Motl,
How readily testable are predictions like the Kaluza-Klein modes? Have
people worked out the cross-section for production and looked at how the
signal would look in the LHC? What about the excited string states? I'm
not really sure if I even understand what you mean by that.

[Moderator's note: Quoted text trimmed to a reasonable amount by
moderator[itex]. -usc][/itex]

Alan

<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 the other hand, the LHC can also discover new material supporting\n> string theory that is unrelated to supersymmetry - namely excited string\n> states; small black holes; Kaluza-Klein modes (particles moving in extra\n> dimensions), and so on. Even if the stringy realization of such models\n> will not be known immediately, such discoveries could be a bigger triumph\n> for string theory than the discovery of supersymmetry.\n\nI agree with this conclusion. Can someone elaborate on how some of these\nwould be\ndetected if they are produced. In particular, I am most curious about\nhow the small black holes might be detected at the LHC under two scenarios:\n(1) they radiate (2) they don\'t. Are detectors being built for both cases?\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 the other hand, the LHC can also discover new material supporting
> string theory that is unrelated to supersymmetry - namely excited string
> states; small black holes; Kaluza-Klein modes (particles moving in extra
> dimensions), and so on. Even if the stringy realization of such models
> will not be known immediately, such discoveries could be a bigger triumph
> for string theory than the discovery of supersymmetry.

I agree with this conclusion. Can someone elaborate on how some of these
would be
detected if they are produced. In particular, I am most curious about
how the small black holes might be detected at the LHC under two scenarios:
(1) they radiate (2) they don't. Are detectors being built for both cases?

Arun Gupta

<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>Suppose LHC discovers yet-another-generation of quarks?\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>Suppose LHC discovers yet-another-generation of quarks?

Lubos Motl

<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, 19 Jul 2004, Creighton Hogg wrote:\n\n> How readily testable are predictions like the Kaluza-Klein modes? Have\n> people worked out the cross-section for production and looked at how the\n> signal would look in the LHC? What about the excited string states? I\'m\n> not really sure if I even understand what you mean by that.\n\nHi Creighton,\n\nall these predictions are testable as long as the LHC has enough energy to\nproduce the particles, quanta of the new fields. KK-modes of the Standard\nModel particles - those only exist in the models without branes, roughly\nspeaking - look like heavier partners of the known particles that would be\nseen, at the LHC, via their decay product because they would probably\ndecay rapidly (like tau) - but anyway, from the decayed particle you can\nmeasure its energy and couplings.\n\nThe KK-modes of weakly interacting particles, such as the graviton (that\nalways exists, even though we don\'t know their masses yet) would not be\nseen inside the detector, and they would manifest themselves as missing\nenergy. Their discovery would be analogous to the discovery of neutrino -\nbut be sure that the dependence of their production rate on various\nparameters has been worked out, and it is even likely that they got the\nnumbers right - which does not guarantee that the theory is right. ;-)\n\nThe excited string modes of the particles also look like heavier partners,\nbut if we were really lucky, we could see a very characteristic spectrum\nof their masses that would coincide with excitations of a string. These\npossibilities are unlikely because the low-energy gravity are not too\nlikely and differ from string theory in 10D, and therefore the mass\nspectrum is not that easy anyway.\n\nBest wishes\nLubos\n________________________________________________________ ______________________\nE-mail: lumo@matfyz.cz fax: +1-617/496-0110 Web: http://lumo.matfyz.cz/\neFax: +1-801/454-1858 work: +1-617/496-8199 home: +1-617/868-4487 (call)\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 Mon, 19 Jul 2004, Creighton Hogg wrote:

> How readily testable are predictions like the Kaluza-Klein modes? Have
> people worked out the cross-section for production and looked at how the
> signal would look in the LHC? What about the excited string states? I'm
> not really sure if I even understand what you mean by that.

Hi Creighton,

all these predictions are testable as long as the LHC has enough energy to
produce the particles, quanta of the new fields. KK-modes of the Standard
Model particles - those only exist in the models without branes, roughly
speaking - look like heavier partners of the known particles that would be
seen, at the LHC, via their decay product because they would probably
decay rapidly (like [itex]\tau) -[/itex] but anyway, from the decayed particle you can
measure its energy and couplings.

The KK-modes of weakly interacting particles, such as the graviton (that
always exists, even though we don't know their masses yet) would not be
seen inside the detector, and they would manifest themselves as missing
energy. Their discovery would be analogous to the discovery of neutrino -
but be sure that the dependence of their production rate on various
parameters has been worked out, and it is even likely that they got the
numbers right - which does not guarantee that the theory is right. ;-)

The excited string modes of the particles also look like heavier partners,
but if we were really lucky, we could see a very characteristic spectrum
of their masses that would coincide with excitations of a string. These
possibilities are unlikely because the low-energy gravity are not too
likely and differ from string theory in 10D, and therefore the mass
spectrum is not that easy anyway.

Best wishes
Lubos
__{____________________________________________________________________ ________}
E-mail: lumo@matfyz.cz fax: [itex]+1-617/496-0110[/itex] Web: http://lumo.matfyz.cz/
eFax: [itex]+1-801/454-1858[/itex] work: [itex]+1-617/496-8199[/itex] home: [itex]+1-617/868-4487[/itex] (call)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^

Lubos Motl

<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, 19 Jul 2004, Alan wrote:\n\n> I agree with this conclusion. Can someone elaborate on how some of\n> these would be detected if they are produced. In particular, I am most\n> curious about how the small black holes might be detected at the LHC\n> under two scenarios: (1) they radiate (2) they don\'t. Are detectors\n> being built for both cases?\n\nIf the black holes are produced by the LHC and Hawking is wrong - they\ndon\'t radiate - we will see their existence for a while, but very easily,\nbecause such a black hole will eat Switzerland and then the rest of our\nblue planet.\n\nThere are good reasons not to be afraid of this combined risk because if\nsuch dangerous black holes could be produced, the stars around would\nprobably not be here anymore. Well, let me be more realistic. Even stable\nblack holes of this small mass would need a long time to absorb matter\naround because their gravity is still too weak. (I have not done\ncalculations how quickly such a black hole grows, has someone done it?)\nBecause such stable black holes are black, they would only be seen as\nmissing energy, an apparent violation of momentum/energy conservation\nlaws.\n\nIf they radiate, a small black hole would be seen as an unstable particle\nthat decays into a very large number of products that are virtually\nisotropically distributed around it. This would be a very unusual,\nshocking signal, that you could not miss.\n________________________________________________________________ ______________\nE-mail: lumo@matfyz.cz fax: +1-617/496-0110 Web: http://lumo.matfyz.cz/\neFax: +1-801/454-1858 work: +1-617/496-8199 home: +1-617/868-4487 (call)\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 Mon, 19 Jul 2004, Alan wrote:

> I agree with this conclusion. Can someone elaborate on how some of
> these would be detected if they are produced. In particular, I am most
> curious about how the small black holes might be detected at the LHC
> under two scenarios: (1) they radiate (2) they don't. Are detectors
> being built for both cases?

If the black holes are produced by the LHC and Hawking is wrong - they
don't radiate [itex]- we[/itex] will see their existence for a while, but very easily,
because such a black hole will eat Switzerland and then the rest of our
blue planet.

There are good reasons not to be afraid of this combined risk because if
such dangerous black holes could be produced, the stars around would
probably not be here anymore. Well, let me be more realistic. Even stable
black holes of this small mass would need a long time to absorb matter
around because their gravity is still too weak. (I have not done
calculations how quickly such a black hole grows, has someone done it?)
Because such stable black holes are black, they would only be seen as
missing energy, an apparent violation of momentum/energy conservation
laws.

If they radiate, a small black hole would be seen as an unstable particle
that decays into a very large number of products that are virtually
isotropically distributed around it. This would be a very unusual,
shocking signal, that you could not miss.
__{____________________________________________________________________ ________}
E-mail: lumo@matfyz.cz fax: [itex]+1-617/496-0110[/itex] Web: http://lumo.matfyz.cz/
eFax: [itex]+1-801/454-1858[/itex] work: [itex]+1-617/496-8199[/itex] home: [itex]+1-617/868-4487[/itex] (call)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^

Haelfix

<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>Hmm, why do you think that if we find more Guage symmetries in nature,\nthat would be bad for String theory?\n\nLets say we observe a rather simple GUT like SO(10). I was under the\nimpression most Stringy toy models often used this as a given (or some\nSO(n) theory, where n might be large) instead of formally reducing to\nthe simple parameter space of the standard model? Or am I way off\nbase.\n\nAnother question(s).. What would a highly enlarged Higgs sector mean\nexactly, and/or the absense of any result. Would the fine tuning scare\npeople out of particle physics, or would we be compelled to rehit the\ndrawing boards.\n\n------------------------------------------------------------------------\nThis post submitted through the LaTeX-enabled physicsforums.com\nTo view this post with LaTeX images:\nhttp://www.physicsforums.com/showthread.php?t=34769#post260648\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>Hmm, why do you think that if we find more Guage symmetries in nature,
that would be bad for String theory?

Lets say we observe a rather simple GUT like SO(10). I was under the
impression most Stringy toy models often used this as a given (or some
SO(n) theory, where n might be large) instead of formally reducing to
the simple parameter space of the standard model? Or am I way off
base.

Another question(s).. What would a highly enlarged Higgs sector mean
exactly, [itex]and/or[/itex] the absense of any result. Would the fine tuning scare
people out of particle physics, or would we be compelled to rehit the
drawing boards.

------------------------------------------------------------------------
This post submitted through the LaTeX-enabled physicsforums.com
To view this post with LaTeX images:
http://www.physicsforums.com/showthr...769#post260648

Urs Schreiber

<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>"Alan" <info@optioncity.REMOVETHIS.net> schrieb im Newsbeitrag\nnews:ltadnXJsTYVXhGHdRVn-rA-100000@adelphia.com...\n\n> Can someone elaborate on how some of these would be\n> detected if they are produced. In particular, I am most curious about\n> how the small black holes might be detected at the LHC under two\nscenarios:\n> (1) they radiate (2) they don\'t. Are detectors being built for both\ncases?\n\nPresumeably you don\'t need different detectors, but have to check the same\ndetector for different signatures.\n\nSignatures of stringy black holes have been computed in a couple of papers.\nSee for instance\n\nK. Cheung:\nBlack hole, string ball, and p-brane production at hadronic supercolliders,\nhttp://arxiv.org/abs/hep-ph/0210242 .\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>"Alan" <info@optioncity.REMOVETHIS.net> schrieb im Newsbeitrag
news:ltadnXJsTYVXhGHdRVn-rA-100000@adelphia.com...

> Can someone elaborate on how some of these would be
> detected if they are produced. In particular, I am most curious about
> how the small black holes might be detected at the LHC under two
scenarios:
> (1) they radiate (2) they don't. Are detectors being built for both
cases?

Presumeably you don't need different detectors, but have to check the same
detector for different signatures.

Signatures of stringy black holes have been computed in a couple of papers.
See for instance

K. Cheung:
Black hole, string ball, and p-brane production at hadronic supercolliders,
http://arxiv.org/abs/http://www.arxi...hep-ph/0210242 .

Creighton Hogg

<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>\n\nOn Tue, 20 Jul 2004, Lubos Motl wrote:\n\n> On Mon, 19 Jul 2004, Creighton Hogg wrote:\n>\n> > How readily testable are predictions like the Kaluza-Klein modes? Have\n> > people worked out the cross-section for production and looked at how the\n> > signal would look in the LHC? What about the excited string states? I\'m\n> > not really sure if I even understand what you mean by that.\n>\n> Hi Creighton,\n>\n> all these predictions are testable as long as the LHC has enough energy to\n> produce the particles, quanta of the new fields. KK-modes of the Standard\n> Model particles - those only exist in the models without branes, roughly\n> speaking - look like heavier partners of the known particles that would be\n> seen, at the LHC, via their decay product because they would probably\n> decay rapidly (like tau) - but anyway, from the decayed particle you can\n> measure its energy and couplings.\n\nWell, I was worried more about being "viably" testable. I haven\'t seen\nmany papers addressing the feasibility of detection in one of the LHC\nexperiments.\n\nFor example,\n> The KK-modes of weakly interacting particles, such as the graviton (that\n> always exists, even though we don\'t know their masses yet) would not be\n> seen inside the detector, and they would manifest themselves as missing\n> energy. Their discovery would be analogous to the discovery of neutrino -\n> but be sure that the dependence of their production rate on various\n> parameters has been worked out, and it is even likely that they got the\n> numbers right - which does not guarantee that the theory is right. ;-)\n\nWell I know that things like the graviton would be seen as a missing\ntransverse energy, but I\'m worried that the cross-section of production is\ntoo low and that the signal would be swamped by a comparatively large\nneutrino background. Afterall, the production cross-section of gravitons\nhas to be proportional to the gravitational constant, which is rather\nsmall. Or would it be proportional to the 10-D gravitational constant\nwhich is much bigger (if I remember right)?\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, 20 Jul 2004, Lubos Motl wrote:

> On Mon, 19 Jul 2004, Creighton Hogg wrote:
>
> > How readily testable are predictions like the Kaluza-Klein modes? Have
> > people worked out the cross-section for production and looked at how the
> > signal would look in the LHC? What about the excited string states? I'm
> > not really sure if I even understand what you mean by that.
>
> Hi Creighton,
>
> all these predictions are testable as long as the LHC has enough energy to
> produce the particles, quanta of the new fields. KK-modes of the Standard
> Model particles - those only exist in the models without branes, roughly
> speaking - look like heavier partners of the known particles that would be
> seen, at the LHC, via their decay product because they would probably
> decay rapidly (like [itex]\tau) -[/itex] but anyway, from the decayed particle you can
> measure its energy and couplings.

Well, I was worried more about being "viably" testable. I haven't seen
many papers addressing the feasibility of detection in one of the LHC
experiments.

For example,
> The KK-modes of weakly interacting particles, such as the graviton (that
> always exists, even though we don't know their masses yet) would not be
> seen inside the detector, and they would manifest themselves as missing
> energy. Their discovery would be analogous to the discovery of neutrino -
> but be sure that the dependence of their production rate on various
> parameters has been worked out, and it is even likely that they got the
> numbers right - which does not guarantee that the theory is right. ;-)

Well I know that things like the graviton would be seen as a missing
transverse energy, but I'm worried that the cross-section of production is
too low and that the signal would be swamped by a comparatively large
neutrino background. Afterall, the production cross-section of gravitons
has to be proportional to the gravitational constant, which is rather
small. Or would it be proportional to the [itex]10-D[/itex] gravitational constant
which is much bigger (if I remember right)?

Alan

<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>\n"Lubos Motl" <motl@feynman.harvard.edu> wrote in message\nnews:Pine.LNX.4.31.0407200002550.25397-100000@einstein.physics.harvard.edu...\n> On Mon, 19 Jul 2004, Alan wrote:\n\n> There are good reasons not to be afraid of this combined risk because if\n> such dangerous black holes could be produced, the stars around would\n> probably not be here anymore. Well, let me be more realistic. Even stable\n> black holes of this small mass would need a long time to absorb matter\n> around because their gravity is still too weak. (I have not done\n> calculations how quickly such a black hole grows, has someone done it?)\n\nThanks, Lubos.\nRegarding the calculation: yes, a poster over in the spr group did a\n"back of the envelope" estimate in a recent thread. The calculation\nsuggests,\nconfirming your intuition, that significant accretion is not a problem, say\nrelative to the life of the sun.\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>"Lubos Motl" <motl@feynman.harvard.edu> wrote in message
news:Pine.LNX.4.31.0407200002550.253...harvard.edu...
> On Mon, 19 Jul 2004, Alan wrote:

> There are good reasons not to be afraid of this combined risk because if
> such dangerous black holes could be produced, the stars around would
> probably not be here anymore. Well, let me be more realistic. Even stable
> black holes of this small mass would need a long time to absorb matter
> around because their gravity is still too weak. (I have not done
> calculations how quickly such a black hole grows, has someone done it?)

Thanks, Lubos.
Regarding the calculation: yes, a poster over in the spr group did a
"back of the envelope" estimate in a recent thread. The calculation
suggests,
confirming your intuition, that significant accretion is not a problem, say
relative to the life of the sun.

Lubos Motl

<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, 20 Jul 2004, Haelfix wrote:\n\n> Hmm, why do you think that if we find more Guage symmetries in nature,\n> that would be bad for String theory?\n\nIt depends which gauge symmetries. A discovery of a grand unified group\nwould be great for string theory - a friend of Grand Unified Theories. ;-)\nWe won\'t discover the GUT group directly, however. The additional gauge\nbosons are very massive - their mass is at the GUT scale which is 10^16 GeV.\nThe GUT group is broken and the LHC can\'t see it directly. This is true\nfor all GUT models I am aware of. The GUT theories are tested indirectly,\nvia their predictions of proton decay etc.\n\nWhen I suggested that the new evidence of new gauge symmetries won\'t\nsupport string theory, I meant some random assorted new gauge symmetries -\nespecially new Z\' bosons, as they\'re called, new broken neutral Abelian\ngauge symmetries. Although many string models in the literature gave us\n(many) new U(1) symmetries - I am thinking about the four-dimensional free\nfermionic heterotic models, for example - I am afraid that their precise\nstructure would not help us too much to make a conceptual or another\nsignificant progress in connecting string theory with reality - unless\nthere will be a shocking pattern that I\'m not able to predict now.\n\nThere can be new confining non-Abelian symmetries, in principle - a\ntotally new particle hyperproton made of hyperquarks - where all these\nparticles are 1000 times heavier than protons and quarks (near the\nhyper-QCD TeV scale). That would be certainly fun for many people, but I\nwould certainly view it as a strange signal that does not confirm any\nprinciple that has been derived from string theory. Of course, later,\npeople could show that such things have a perfect stringy explanation ;-),\nbut I can\'t write a whole book of fiction what could happen because the\nspectrum of such possibilities is huge.\n\n> Lets say we observe a rather simple GUT like SO(10). I was under the\n> impression most Stringy toy models often used this as a given (or some\n> SO(n) theory, where n might be large) instead of formally reducing to\n> the simple parameter space of the standard model? Or am I way off\n> base.\n\nPerhaps, I don\'t understand your text enough to reply. String theory can\nconstruct SO(10) GUT, E6 GUT, SU(5) GUT, the Standard Model plus various\nhidden groups, and so on - all these possibilities can be realized within\nstring theory in many different ways. It does not seem that any particular\nsolution would help us to find TOE - but of course, the confirmation of\nGUT would be amazing. Another comment: we can\'t see GUT directly at the\nLHC, and the LHC also can\'t distinguish between different GUT scenarios.\nThe LHC can only see new symmetries that are broken or confined at a few\nTeV.\n\n> Another question(s).. What would a highly enlarged Higgs sector mean\n> exactly, and/or the absense of any result. Would the fine tuning scare\n> people out of particle physics, or would we be compelled to rehit the\n> drawing boards.\n\nI am not a specialist, so my comments can be off the board. But the\nfine-tuning is not necessarily correlated with the size of the Higgs\nsector. If there is a single fundamental Higgs doublet, it is likely that\nwe will have to live with the idea that the Standard Model is essentially\ncomplete up to many TeVs, and Nature is fine-tuned whether we like it or\nnot.\n\nIf there are two Higgs doublets, such as in SUSY models, the hierarchy can\nbe protected by SUSY. Already today, the masses of superpartners are clear\nto be slightly higher than what would be perfectly solving the hierarchy\nproblem.\n\nVarious people in physics hate the fundamental scalar fields, and they\npropose that the Higgs must be composite, with a new strongly coupled\ngroup at a TeV scale - technicolor-like models (another pseudosolution of\nthe hierarchy problem). I would say that this approach is almost exactly\ncontrary to the thinking in string theory, and if the Higgs were shown to\nbe made of techniquarks, string theory would almost certainly be in\ntrouble for a while - at least because such models have not been studied\nmuch in the stringy context as far as I know.\n\nString theory does not favor the "preon" religion - the religion that says\nthat everything, including gauge bosons, should be made of fundamental\nspin-1/2 particles. String theory has no problem at all to generate\ngravity; fundamental gauge fields with spin 1; and fundamental scalars\n(with spin 0). They are equally fundamental as spin 1/2 particles. In\nfact, string theory often generates too many scalars. There can be many\nHiggses etc., but it seems fair to say that the Higgs(es) in string theory\nhave been almost always fundamental fields, not composites.\n\nJust like the discovery of SUSY; GUT; KK modes; excited strings; even\nfractional charges would be a supportive news for string theory, I think\nthat the discovery of new chaotic particles; preons; composite Higgs;\ncompositeness of other Standard Model particles - all these things would\nbe setback for string theory, I think, and they would support other\nbranches of particle phenomenology.\n\nThe minimal Standard Model with a single Higgs would be a sort of neutral\nresult. We would, in some sense, know as much as we know today (with a\ndifferent upper limit of validity of the Standard Model). The precise\nmodels that proposed new physics at the LHC would be eliminated, and\nanalogous models based on the same principles, but using higher energies,\nwould compete according to virtually unchanged rules. All approaches that\nneeded a relatively low scale to be natural - not only SUSY, but virtually\nanything solving the hierarchy problem - would be uniformly weakened, and\nthe anthropic principle and the possibility of fine-tuning would be\nstrengthened.\n\nThe same holds for other non-conceptual discoveries such as potential\nheavy generations of quarks and leptons (they should still come together,\nfor anomalies to cancel). If we were able to see many generations, we\nmight get more hints to see the patterns in masses. But if it is not so, I\nthink that no specific subculture in particle physics would be\nstrengthened. None really care whether there is a 4th heavy generation of\nfermions.\n\nOf course, a confirmation of any specific model that has appeared in the\nliterature would be a huge victory for the author(s) of the model, and\n(s)he would gain a big influence on the development of particle physics.\nThe number of possibilities is huge - but I tend to think that the first\nfound beautiful possibilities that survived - such as SUSY - are still\nmost likely. If SUSY is found, we will be saying that we were just trying\nto waste time before the new experiments by studying alternative models.\nOf course, if SUSY is not found, we will be saying that we had been\nwasting time with SUSY. ;-)\n____________________________________________________________________ __________\nE-mail: lumo@matfyz.cz fax: +1-617/496-0110 Web: http://lumo.matfyz.cz/\neFax: +1-801/454-1858 work: +1-617/496-8199 home: +1-617/868-4487 (call)\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 Tue, 20 Jul 2004, Haelfix wrote:

> Hmm, why do you think that if we find more Guage symmetries in nature,
> that would be bad for String theory?

It depends which gauge symmetries. A discovery of a grand unified group
would be great for string theory - a friend of Grand Unified Theories. ;-)
We won't discover the GUT group directly, however. The additional gauge
bosons are very massive - their mass is at the GUT scale which is [itex]10^16[/itex] GeV.
The GUT group is broken and the LHC can't see it directly. This is true
for all GUT models I am aware of. The GUT theories are tested indirectly,
via their predictions of proton decay etc.

When I suggested that the new evidence of new gauge symmetries won't
support string theory, I meant some random assorted new gauge symmetries -
especially new Z' bosons, as they're called, new broken neutral Abelian
gauge symmetries. Although many string models in the literature gave us
(many) new U(1) symmetries [itex]- I am[/itex] thinking about the four-dimensional free
fermionic heterotic models, for example [itex]- I am[/itex] afraid that their precise
structure would not help us too much to make a conceptual or another
significant progress in connecting string theory with reality - unless
there will be a shocking pattern that I'm not able to predict now.

There can be new confining non-Abelian symmetries, in principle - a
totally new particle hyperproton made of hyperquarks - where all these
particles are 1000 times heavier than protons and quarks (near the
hyper-QCD TeV scale). That would be certainly fun for many people, but I
would certainly view it as a strange signal that does not confirm any
principle that has been derived from string theory. Of course, later,
people could show that such things have a perfect stringy explanation ;-),
but I can't write a whole book of fiction what could happen because the
spectrum of such possibilities is huge.

> Lets say we observe a rather simple GUT like SO(10). I was under the
> impression most Stringy toy models often used this as a given (or some
> SO(n) theory, where n might be large) instead of formally reducing to
> the simple parameter space of the standard model? Or am I way off
> base.

Perhaps, I don't understand your text enough to reply. String theory can
construct SO(10) GUT, E6 GUT, SU(5) GUT, the Standard Model plus various
hidden groups, and so on - all these possibilities can be realized within
string theory in many different ways. It does not seem that any particular
solution would help us to find TOE - but of course, the confirmation of
GUT would be amazing. Another comment: we can't see GUT directly at the
LHC, and the LHC also can't distinguish between different GUT scenarios.
The LHC can only see new symmetries that are broken or confined at a few
TeV.

> Another question(s).. What would a highly enlarged Higgs sector mean
> exactly, [itex]and/or[/itex] the absense of any result. Would the fine tuning scare
> people out of particle physics, or would we be compelled to rehit the
> drawing boards.

I am not a specialist, so my comments can be off the board. But the
fine-tuning is not necessarily correlated with the size of the Higgs
sector. If there is a single fundamental Higgs doublet, it is likely that
we will have to live with the idea that the Standard Model is essentially
complete up to many TeVs, and Nature is fine-tuned whether we like it or
not.

If there are two Higgs doublets, such as in SUSY models, the hierarchy can
be protected by SUSY. Already today, the masses of superpartners are clear
to be slightly higher than what would be perfectly solving the hierarchy
problem.

Various people in physics hate the fundamental scalar fields, and they
propose that the Higgs must be composite, with a new strongly coupled
group at a TeV scale - technicolor-like models (another pseudosolution of
the hierarchy problem). I would say that this approach is almost exactly
contrary to the thinking in string theory, and if the Higgs were shown to
be made of techniquarks, string theory would almost certainly be in
trouble for a while [itex]- at[/itex] least because such models have not been studied
much in the stringy context as far as I know.

String theory does not favor the "preon" religion - the religion that says
that everything, including gauge bosons, should be made of fundamental
spin-1/2 particles. String theory has no problem at all to generate
gravity; fundamental gauge fields with spin 1; and fundamental scalars
(with spin 0). They are equally fundamental as spin 1/2 particles. In
fact, string theory often generates too many scalars. There can be many
Higgses etc., but it seems fair to say that the Higgs(es) in string theory
have been almost always fundamental fields, not composites.

Just like the discovery of SUSY; GUT; KK modes; excited strings; even
fractional charges would be a supportive news for string theory, I think
that the discovery of new chaotic particles; preons; composite Higgs;
compositeness of other Standard Model particles - all these things would
be setback for string theory, I think, and they would support other
branches of particle phenomenology.

The minimal Standard Model with a single Higgs would be a sort of neutral
result. We would, in some sense, know as much as we know today (with a
different upper limit of validity of the Standard Model). The precise
models that proposed new physics at the LHC would be eliminated, and
analogous models based on the same principles, but using higher energies,
would compete according to virtually unchanged rules. All approaches that
needed a relatively low scale to be natural - not only SUSY, but virtually
anything solving the hierarchy problem - would be uniformly weakened, and
the anthropic principle and the possibility of fine-tuning would be
strengthened.

The same holds for other non-conceptual discoveries such as potential
heavy generations of quarks and leptons (they should still come together,
for anomalies to cancel). If we were able to see many generations, we
might get more hints to see the patterns in masses. But if it is not so, I
think that no specific subculture in particle physics would be
strengthened. None really care whether there is a 4th heavy generation of
fermions.

Of course, a confirmation of any specific model that has appeared in the
literature would be a huge victory for the author(s) of the model, and
(s)he would gain a big influence on the development of particle physics.
The number of possibilities is huge - but I tend to think that the first
found beautiful possibilities that survived - such as SUSY - are still
most likely. If SUSY is found, we will be saying that we were just trying
to waste time before the new experiments by studying alternative models.
Of course, if SUSY is not found, we will be saying that we had been
wasting time with SUSY. ;-)
__{____________________________________________________________________ ________}
E-mail: lumo@matfyz.cz fax: [itex]+1-617/496-0110[/itex] Web: http://lumo.matfyz.cz/
eFax: [itex]+1-801/454-1858[/itex] work: [itex]+1-617/496-8199[/itex] home: [itex]+1-617/868-4487[/itex] (call)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^

Pam Crouch

<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>Oh, I see, so everyone is in agreement about all the details of string\ntheory, and it is undeniably established that strings are the\n*only*possible* explanation for a zero-mass particle with two degrees of\nspin? If that were the case would there be a need to discuss string theory\nin this forum? That\'s what I\'m referring to. Sorry if I didn\'t state it\nprecisely enough for you.\n\n--Pam\n\n\n"Ulmo" <ulmo@cheerful.com> wrote in message\nnews:53ca460a.0407141212.3601b29c-100000@posting.google.com...\n> Pam Crouch <jasonpam@nospammingswbell.net> wrote in message\nnews:<QTBIc.14797\\$EN.2638-100000@newssvr24.news.prodigy.com>...\n>\n> > I\'m curious; assuming string theory can be reconciled with existing\nphysics\n> > theories,\n>\n> What do you mean "reconciled"? All theories are an extension of\n> previous theories. There has never been anything in string theory that\n> is inconsistent with observation.\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>Oh, I see, so everyone is in agreement about all the details of string
theory, and it is undeniably established that strings are the
*only*possible* explanation for a zero-mass particle with two degrees of
spin? If that were the case would there be a need to discuss string theory
in this forum? That's what I'm referring to. Sorry if I didn't state it
precisely enough for you.

--Pam

"Ulmo" <ulmo@cheerful.com> wrote in message
news:53ca460a.0407141212.3601b29c-10....google.com...
> Pam Crouch <jasonpam@nospammingswbell.net> wrote in message
news:<QTBIc.14797$EN.2638-100000@new...rodigy.com>...
>
> > I'm curious; assuming string theory can be reconciled with existing
physics
> > theories,
>
> What do you mean "reconciled"? All theories are an extension of
> previous theories. There has never been anything in string theory that
> is inconsistent with observation.
>
>

Arun Gupta

<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>Pam Crouch <jasonpam@nospammingswbell.net> wrote in message news:<wlgLc.15327\\$4F1.9104-100000@newssvr23.news.prodigy.com>...\n> Oh, I see, so everyone is in agreement about all the details of string\n> theory, and it is undeniably established that strings are the\n> *only*possible* explanation for a zero-mass particle with two degrees of\n> spin? If that were the case would there be a need to discuss string theory\n> in this forum? That\'s what I\'m referring to. Sorry if I didn\'t state it\n> precisely enough for you.\n\nI think the question should be - is there any experiment possible whose\noutcome would rule out string theory?\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>Pam Crouch <jasonpam@nospammingswbell.net> wrote in message news:<wlgLc.15327$4F1.9104-100000@ne...rodigy.com>...
> Oh, I see, so everyone is in agreement about all the details of string
> theory, and it is undeniably established that strings are the
> *only*possible* explanation for a zero-mass particle with two degrees of
> spin? If that were the case would there be a need to discuss string theory
> in this forum? That's what I'm referring to. Sorry if I didn't state it
> precisely enough for you.

I think the question should be - is there any experiment possible whose
outcome would rule out string theory?

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