<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>Probably my question is not well posed. But hopefully people can clarify.\n\nI am reading Will\'s article: "confrontation between GR and experiment" which is\nhttp://www.arxiv.org/abs/gr-qc/0103036\n\nOn pg 5 it is mentioned that superstring theory is not a metric theory of\ngravity leading to violations of equivalence principle.\n\nMy question is at what scale is violation of equivalence principle expected\nin the popular string theory models?\n\nIn other words can string theory make a prediction on what will be the value\nof neta(figure 1) of this paper?\n\nOr is my question meaningless?\n\nThanks\nMelroy\n\n\n[Moderator\'s note: String theory backgrounds with exactly massless scalars\n(moduli are the clearest example) would lead to new long-range forces.\nThe coupling of the scalar fields to other matter is non-universal, and\ntherefore the acceleration would depend on the type of the matter, and\nyou can view it as a violation of the principle of equivalence. It is\nmore or less assumed that realistic vacua of string theory are not\nallowed to include any exactly massless scalars - otherwise the model\nwould contradict high-precision measurements of the equivalence\nprinciple. String theory vacua with no massless scalar fields (all scalar\nfields being massive) implies the equivalence principle exactly.\nIf I am saying something incorrectly, please correct me. LM]\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>Probably my question is not well posed. But hopefully people can clarify.
I am reading Will's article: "confrontation between GR and experiment" which is
http://www.arxiv.org/abs/http://www.arxiv.org/abs/gr-qc/0103036
On pg 5 it is mentioned that superstring theory is not a metric theory of
gravity leading to violations of equivalence principle.
My question is at what scale is violation of equivalence principle expected
in the popular string theory models?
In other words can string theory make a prediction on what will be the value
of neta(figure 1) of this paper?
Or is my question meaningless?
Thanks
Melroy
[Moderator's note: String theory backgrounds with exactly massless scalars
(moduli are the clearest example) would lead to new long-range forces.
The coupling of the scalar fields to other matter is non-universal, and
therefore the acceleration would depend on the type of the matter, and
you can view it as a violation of the principle of equivalence. It is
more or less assumed that realistic vacua of string theory are not
allowed to include any exactly massless scalars - otherwise the model
would contradict high-precision measurements of the equivalence
principle. String theory vacua with no massless scalar fields (all scalar
fields being massive) implies the equivalence principle exactly.
If I am saying something incorrectly, please correct me. LM]
Robert C. Helling
Oct28-04, 04:09 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, 27 Oct 2004 16:39:01 -0400, Melroy <melroysoares@hotmail.com> wrote:\n\n> On pg 5 it is mentioned that superstring theory is not a metric theory of\n> gravity leading to violations of equivalence principle.\n\n> In other words can string theory make a prediction on what will be the value\n> of neta(figure 1) of this paper?\n>\n>\n> [Moderator\'s note: String theory backgrounds with exactly massless scalars\n> (moduli are the clearest example) would lead to new long-range forces.\n\n> principle. String theory vacua with no massless scalar fields (all scalar\n> fields being massive) implies the equivalence principle exactly.\n> If I am saying something incorrectly, please correct me. LM]\n\n[First: Lubos, if you have to say something about physics write a\nfollow up, moderators comments are for meta-information! It is awkward\nto reply to moderator comments as it looks like I am replying to the\noriginal post. Furthermore it is extremely rude (i know you don\'t care\nabout this) to the original poster to distort his posting by the\ninjection of your comments, especially if you do not agree. See an\nearlier thread, you know which.]\n\nWhat you say is essentially right, however there can be exceptions:\nThere can be light, unobserved scalar fields if their coupling to\nmatter is very weak. See Will\'s review for details, but the coupling\nwould have to be orders of magnitude smaller than gravitational\ncoupling which is already pretty weak.\n\nOTOH, massive above should mean that the mass is such that the\nparticle does not survive to travel over distances over which the\nequivalence principle is tested, i.e. solar system distances. That\nsets a (admittedly) weak lower bound on the mass.\n\nThe weak coupling at first sounds like a possibility but remember that\nthis would have to be stable under renormalization and thus again,\nthere is fine tuning evolved.\n\nTo the original post: String models that have been studied in the past\nusually contain many massless scalar fields (moduli) with couplings of\norder one to matter fields. Those are therefore in conflict with WEP\nexperiments. However, the existence of exact moduli might be an\nartefact of the assumed (N=2) supersymmetry that simplifies the\nanalysis of the models and might not be there in generic string models\nwith only N=1 or no supersymmetry. There has been a lot of progress in\nthis direction recently and this whole landscape business is about\nstring compactifications with possibly no light scalar fields (you\nwill read this in the form of \'all moduli are frozen\').\n\nSome people speculate that there might be some physical process that\nrenders scalar fields effectively invisible (there only particle of\nthe standard model that has not been observed yet is the only\nscalar!), Stephen Hawking has written papers in this direction (he\nclaims some scattering with virtual black holes could be responsible\nfor this) and when asked recently he told me that he thus expects that\nno Higgs will be found at LHC. We\'ll see.\n\nOn the other hand, there is a naturalness argument: That would suggest\nthat quantum effects generically give a renormalized mass of order of\nthe Planck scale to all particles if there is no other reason that\nprevents this. Usually, symmetries are the standard mechanism that\nimpose masslessness of particles: Gauge symmetries impose masslessness\nof vectors and chiral symmetry requires fermions to be\nmassless. Viewed from the Planck scale, all standard model particles\nare effectively massless and there are these symmetries that protect\nthis (some symmetries are not exact and thus allow small\nmasses). However there is no symmetry that protects the smallness of\nthe mass of the Higgs and this is just another way to state the\nhierarchy problem. Here susy comes to a rescue as it would provide the\nmechanism to keep the Higgs mass small (i.e. at the weak scale).\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 School of Science and Engineering\nInternational University Bremen\nprint "Just another Phone: +49 421-200 3574\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 Wed, 27 Oct 2004 16:39:01 -0400, Melroy <melroysoares@hotmail.com> wrote:
> On pg 5 it is mentioned that superstring theory is not a metric theory of
> gravity leading to violations of equivalence principle.
> In other words can string theory make a prediction on what will be the value
> of neta(figure 1) of this paper?
>
>
> [Moderator's note: String theory backgrounds with exactly massless scalars
> (moduli are the clearest example) would lead to new long-range forces.
> principle. String theory vacua with no massless scalar fields (all scalar
> fields being massive) implies the equivalence principle exactly.
> If I am saying something incorrectly, please correct me. LM]
[First: Lubos, if you have to say something about physics write a
follow up, moderators comments are for meta-information! It is awkward
to reply to moderator comments as it looks like I am replying to the
original post. Furthermore it is extremely rude (i know you don't care
about this) to the original poster to distort his posting by the
injection of your comments, especially if you do not agree. See an
earlier thread, you know which.]
What you say is essentially right, however there can be exceptions:
There can be light, unobserved scalar fields if their coupling to
matter is very weak. See Will's review for details, but the coupling
would have to be orders of magnitude smaller than gravitational
coupling which is already pretty weak.
OTOH, massive above should mean that the mass is such that the
particle does not survive to travel over distances over which the
equivalence principle is tested, i.e. solar system distances. That
sets a (admittedly) weak lower bound on the mass.
The weak coupling at first sounds like a possibility but remember that
this would have to be stable under renormalization and thus again,
there is fine tuning evolved.
To the original post: String models that have been studied in the past
usually contain many massless scalar fields (moduli) with couplings of
order one to matter fields. Those are therefore in conflict with WEP
experiments. However, the existence of exact moduli might be an
artefact of the assumed (N=2) supersymmetry that simplifies the
analysis of the models and might not be there in generic string models
with only N=1 or no supersymmetry. There has been a lot of progress in
this direction recently and this whole landscape business is about
string compactifications with possibly no light scalar fields (you
will read this in the form of 'all moduli are frozen').
Some people speculate that there might be some physical process that
renders scalar fields effectively invisible (there only particle of
the standard model that has not been observed yet is the only
scalar!), Stephen Hawking has written papers in this direction (he
claims some scattering with virtual black holes could be responsible
for this) and when asked recently he told me that he thus expects that
no Higgs will be found at LHC. We'll see.
On the other hand, there is a naturalness argument: That would suggest
that quantum effects generically give a renormalized mass of order of
the Planck scale to all particles if there is no other reason that
prevents this. Usually, symmetries are the standard mechanism that
impose masslessness of particles: Gauge symmetries impose masslessness
of vectors and chiral symmetry requires fermions to be
massless. Viewed from the Planck scale, all standard model particles
are effectively massless and there are these symmetries that protect
this (some symmetries are not exact and thus allow small
masses). However there is no symmetry that protects the smallness of
the mass of the Higgs and this is just another way to state the
hierarchy problem. Here susy comes to a rescue as it would provide the
mechanism to keep the Higgs mass small (i.e. at the weak scale).
Robert
--
..oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo. oOo.oOo.oOo.oOo.oOo.oOo.oOo.oO
Robert C. Helling School of Science and Engineering
International University Bremen
print "Just another Phone: +49 421-200 3574
stupid .sig\n"; http://www.aei-potsdam.mpg.de/~helling
http://arxiv.org/ftp/physics/papers/0601/0601218.pdf
A Theory of Quantum Gravity may not be possible because Quantum Mechanics violates the Equivalence Principle
Authors: Mario Rabinowitz
Comments: Easy to follow original proof of the incompatibility of General Relativity and Quantum Mechanics
Subj-class: General Physics; Classical Physics
Quantum mechanics clearly violates the weak equivalence principle (WEP). This implies that quantum mechanics also violates the strong equivalence principle (SEP), as shown in this paper. Therefore a theory of quantum gravity may not be possible unless it is not based upon the equivalence principle, or if quantum mechanics can eliminate its mass dependence. Neither of these possibilities seem likely at the present time
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