View Full Version : "experimental observation of stringy behavior"???
<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>In the very first line of the following paper\n\nhttp://arxiv.org/abs/hep-th/0212061\n\nthe author, in a casual off-hand way, makes the following shocking\nclaim\n\n\n"Since the experimental observation of stringy behavior in hadronic\nphysics..."\n\nWhat\'s he talking about? There is no experimental evidence for string\ntheory at all. He does not cite any references for this claim. What,\nif anything, is he referring to?\n\nDavid\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>In the very first line of the following paper
http://arxiv.org/abs/http://www.arxiv.org/abs/hep-th/0212061
the author, in a casual off-hand way, makes the following shocking
claim
"Since the experimental observation of stringy behavior in hadronic
physics..."
What's he talking about? There is no experimental evidence for string
theory at all. He does not cite any references for this claim. What,
if anything, is he referring to?
David
Urs Schreiber
May26-04, 05:47 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> schrieb im Newsbeitrag\nnews:53ca460a.0405251415.3eee8747-100000@posting.google.com...\n\n> In the very first line of the following paper\n>\n> http://arxiv.org/abs/hep-th/0212061\n>\n> the author, in a casual off-hand way, makes the following shocking\n> claim\n>\n>\n> "Since the experimental observation of stringy behavior in hadronic\n> physics..."\n>\n> What\'s he talking about?\n\nString-gauge duality!\n\nString theory orginiated in the observation that some phenomena in gauge\ntheories are string-like, and after a temporary divorce it has come back\nfull circle to gauge theory again, in the form of holography, AdS/CFT, etc.\n\nThere are at least tWo ways to see strings emerge in ordinary gauge\ntheories: One is in the form of flux tubes, and the other in the form of\nFeynman diagrams.\n\nI assume that the first sentence of the above paper refers to the phenomenon\nof flux tubes, tubes of colour-electric flux lines that arise in confining\ngauge theories in the infra red (but hopefully some expert will correct me\nif that\'s not quite right). These flux tubes are like \'fat\' strings (fat\nmeaning that they have a diameter, as opposed to the abstract fundamental\nstrings).\n\nThe other way to see strings in gauge theory is the famous observation by\nt\'Hooft that in the limit of large N for SU(N) gauge theories the amplitude\nof a given Feynman diagram is proportional to\n\nN^\\xi\n\nwhere \\xi is the Euler characteristic of the Feynman diagram, i.e. the\nnumber of loops in the diagram plus the number of vertices minus the number\nof edges. This is analogous to how the amplitudes of a closed fundamental\nstring goes with g^\\xi, too, where g is the string\'s coupling constant and\n\\xi the Euler number of the worldsheet.\n\nEven better, in the "double scaling limit" of the gauge theory where N goes\nto infinity and the gauge gauge coupling tends to 0 only the planar Feynman\ndiagrams survive and lots of gluon exchange in the generic Feynman diagram\ntends to "fill" the diagram, making it look like a discrete approximation to\na smooth surface - a string.\n\nYou can find a nice simple summary of these facts for instance on the first\ncouple of pages of\n\nMassimo Bianchi\nTrieste lectures on AdS/CFT\nwww.pr.infn.it/snft/2003/Bianchi/bianchi.ps .\n\nIncidentally, there is at least one more fascinating way to see strings\nemergy from Yang-Mills theory: When a YM theory is totally dimensionally\nreduced, i.e. when all the gauge fields are assumed to be independent of the\nspacetime coordinates, being then just large NxN constant matrices, one can\nbuild Wilson line observables in an abstract, auxiliary "space" by taking\nthe expectation value of the coulour flux with respect to some auxiliary\nvector field on an abstract circle (i.e. one that is not embedded in the\nspace that the gauge theory lives on). The Schwinger-Dyson equation of\nmotion of these Wilson line observables of totally dimensionally reduced YM\ntheory can be shown to be nothing but the equations of motion of closed\nstring field theory, where the closed strings are the above mentioned\n"abstract circles" that live in the "auxiliary" space.\n\nI have assembled some literature to this so-called "IIB matrix model" as\nwell as a sketch of this calculation at\n\nhttp://golem.ph.utexas.edu/string/archives/000314.html .\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> schrieb im Newsbeitrag
news:53ca460a.0405251415.3eee8747-100000@posting.google.com...
> In the very first line of the following paper
>
> http://arxiv.org/abs/http://www.arxiv.org/abs/hep-th/0212061
>
> the author, in a casual off-hand way, makes the following shocking
> claim
>
>
> "Since the experimental observation of stringy behavior in hadronic
> physics..."
>
> What's he talking about?
String-gauge duality!
String theory orginiated in the observation that some phenomena in gauge
theories are string-like, and after a temporary divorce it has come back
full circle to gauge theory again, in the form of holography, AdS/CFT, etc.
There are at least tWo ways to see strings emerge in ordinary gauge
theories: One is in the form of flux tubes, and the other in the form of
Feynman diagrams.
I assume that the first sentence of the above paper refers to the phenomenon
of flux tubes, tubes of colour-electric flux lines that arise in confining
gauge theories in the infra red (but hopefully some expert will correct me
if that's not quite right). These flux tubes are like 'fat' strings (fat
meaning that they have a diameter, as opposed to the abstract fundamental
strings).
The other way to see strings in gauge theory is the famous observation by
t'Hooft that in the limit of large N for SU(N) gauge theories the amplitude
of a given Feynman diagram is proportional to
N^\xi
where \xi is the Euler characteristic of the Feynman diagram, i.e. the
number of loops in the diagram plus the number of vertices minus the number
of edges. This is analogous to how the amplitudes of a closed fundamental
string goes with g^\xi, too, where g is the string's coupling constant and
\xi the Euler number of the worldsheet.
Even better, in the "double scaling limit" of the gauge theory where N goes
to infinity and the gauge gauge coupling tends to only the planar Feynman
diagrams survive and lots of gluon exchange in the generic Feynman diagram
tends to "fill" the diagram, making it look like a discrete approximation to
a smooth surface - a string.
You can find a nice simple summary of these facts for instance on the first
couple of pages of
Massimo Bianchi
Trieste lectures on AdS/CFT
www.pr.infn.it/snft/2003/Bianchi/bianchi.ps .
Incidentally, there is at least one more fascinating way to see strings
emergy from Yang-Mills theory: When a YM theory is totally dimensionally
reduced, i.e. when all the gauge fields are assumed to be independent of the
spacetime coordinates, being then just large NxN constant matrices, one can
build Wilson line observables in an abstract, auxiliary "space" by taking
the expectation value of the coulour flux with respect to some auxiliary
vector field on an abstract circle (i.e. one that is not embedded in the
space that the gauge theory lives on). The Schwinger-Dyson equation of
motion of these Wilson line observables of totally dimensionally reduced YM
theory can be shown to be nothing but the equations of motion of closed
string field theory, where the closed strings are the above mentioned
"abstract circles" that live in the "auxiliary" space.
I have assembled some literature to this so-called "IIB matrix model" as
well as a sketch of this calculation at
http://golem.ph.utexas.edu/string/archives/000314.html .
Kris Kennaway
May26-04, 10:08 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 2004-05-26, Ulmo <ulmo@cheerful.com> wrote:\n> In the very first line of the following paper\n>\n> http://arxiv.org/abs/hep-th/0212061\n>\n> the author, in a casual off-hand way, makes the following shocking\n> claim\n>\n>\n> "Since the experimental observation of stringy behavior in hadronic\n> physics..."\n>\n> What\'s he talking about? There is no experimental evidence for string\n> theory at all. He does not cite any references for this claim. What,\n> if anything, is he referring to?\n\nThe confined flux tubes in QCD have stringy behaviour. In fact modern\nstring theory emerged from an attempt to model the strong\ninteractions. It turns out to not nearly be this simple because\n"string theory" is also a theory of gravity, but "stringy behaviour in\nhadronic physics" is real. You can compute things like confining\nstring tensions numerically in lattice QCD, and analytically in N=1\nsupersymmetric theories. OK, I don\'t know about the experimental\nobservations first-hand, but there\'s no reason you couldn\'t go and\ncheck the lattice results against experiment.\n\nThere isn\'t a quantitative reformulation of QCD in terms of the flux\nstrings, although many people hope that "string theory" will yet\nprovide it (indeed, "string theory" does let you do analytic\ncomputations about supersymmetric versions of Yang-Mills and QCD).\n\nKris\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 2004-05-26, Ulmo <ulmo@cheerful.com> wrote:
> In the very first line of the following paper
>
> http://arxiv.org/abs/http://www.arxiv.org/abs/hep-th/0212061
>
> the author, in a casual off-hand way, makes the following shocking
> claim
>
>
> "Since the experimental observation of stringy behavior in hadronic
> physics..."
>
> What's he talking about? There is no experimental evidence for string
> theory at all. He does not cite any references for this claim. What,
> if anything, is he referring to?
The confined flux tubes in QCD have stringy behaviour. In fact modern
string theory emerged from an attempt to model the strong
interactions. It turns out to not nearly be this simple because
"string theory" is also a theory of gravity, but "stringy behaviour in
hadronic physics" is real. You can compute things like confining
string tensions numerically in lattice QCD, and analytically in N=1
supersymmetric theories. OK, I don't know about the experimental
observations first-hand, but there's no reason you couldn't go and
check the lattice results against experiment.
There isn't a quantitative reformulation of QCD in terms of the flux
strings, although many people hope that "string theory" will yet
provide it (indeed, "string theory" does let you do analytic
computations about supersymmetric versions of Yang-Mills and QCD).
Kris
Robert C. Helling
May27-04, 05:18 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, 26 May 2004 10:08:09 -0400, Kris Kennaway <kkenn@xor.obsecurity.org> wrote:\n\n> The confined flux tubes in QCD have stringy behaviour.\n\nIn fact, it wasn\'t just the naive picture of a meson (two quarks with\na flux tube connecting them) looking like an open string but there was\na lot of experimental evidence: The regge behaviour both at positive\nand negative t mentioned in chapter one of GSW and reviewed in greater\ndepth (including real data) for example in\n\nSTRINGS AND SUPERSTRINGS.\nBy Michael B. Green (Queen Mary, U. of London),. 1987. 12pp.\nPublished in Phys.Scripta T15:7-18,1987\n\nIs there any understanding of this from a fundamental theory (ie QCD)\nwhy this string like scattering behaviour is observed in nature?\n\nRobert\n\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 Wed, 26 May 2004 10:08:09 -0400, Kris Kennaway <kkenn@xor.obsecurity.org> wrote:
> The confined flux tubes in QCD have stringy behaviour.
In fact, it wasn't just the naive picture of a meson (two quarks with
a flux tube connecting them) looking like an open string but there was
a lot of experimental evidence: The regge behaviour both at positive
and negative t mentioned in chapter one of GSW and reviewed in greater
depth (including real data) for example in
STRINGS AND SUPERSTRINGS.
By Michael B. Green (Queen Mary, U. of London),. 1987. 12pp.
Published in Phys.Scripta T15:7-18,1987
Is there any understanding of this from a fundamental theory (ie QCD)
why this string like scattering behaviour is observed in nature?
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
Lubos Motl
May27-04, 09:47 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, 27 May 2004, Robert C. Helling wrote:\n\n> In fact, it wasn\'t just the naive picture of a meson (two quarks with\n> a flux tube connecting them) looking like an open string but there was\n> a lot of experimental evidence: The regge ...\n> ...\n> Is there any understanding of this from a fundamental theory (ie QCD)\n> why this string like scattering behaviour is observed in nature?\n\nThese flux tubes, behaving as strings, are a strongly coupled phenomenon\nfrom the gauge theory point of view, and therefore they can\'t be studied\nperturbatively. Nevertheless this stringy behavior is there, and new\ninsights about it have been found in the context of the AdS/CFT\ncorrespondence. I think it is fair to say that Juan Maldacena revived the\nold picture of strings behind the strong interactions - a picture that\ngave birth to string theory.\n\nOtherwise these stringy QCD effects are seen in numerical/lattice\ncalculations, too, but the real QCD is not a great approximation of\nperturbative string theory in a mildly curved space because 3 from SU(3)\nis not quite infinity, although it is close (if counted by 1/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 Thu, 27 May 2004, Robert C. Helling wrote:
> In fact, it wasn't just the naive picture of a meson (two quarks with
> a flux tube connecting them) looking like an open string but there was
> a lot of experimental evidence: The regge ...
> ...
> Is there any understanding of this from a fundamental theory (ie QCD)
> why this string like scattering behaviour is observed in nature?
These flux tubes, behaving as strings, are a strongly coupled phenomenon
from the gauge theory point of view, and therefore they can't be studied
perturbatively. Nevertheless this stringy behavior is there, and new
insights about it have been found in the context of the AdS/CFT
correspondence. I think it is fair to say that Juan Maldacena revived the
old picture of strings behind the strong interactions - a picture that
gave birth to string theory.
Otherwise these stringy QCD effects are seen in numerical/lattice
calculations, too, but the real QCD is not a great approximation of
perturbative string theory in a mildly curved space because 3 from SU(3)
is not quite infinity, although it is close (if counted by 1/N).
__{_______________________________________________ _____________________________}
E-mail: lumo@matfyz.cz fax: +1-617/496-0110 Web: http://lumo.matfyz.cz/
eFax: +1-801/454-1858 work: +1-617/496-8199 home: +1-617/868-4487 (call)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Robert C. Helling
May28-04, 05:55 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, 27 May 2004 09:47:36 -0400, Lubos Motl <motl@feynman.harvard.edu> wrote:\n\n> Otherwise these stringy QCD effects are seen in numerical/lattice\n> calculations, too, but the real QCD is not a great approximation of\n> perturbative string theory in a mildly curved space because 3 from SU(3)\n> is not quite infinity, although it is close (if counted by 1/N).\n\nThe lattice calculations show that QCD contains Regge trajectories but\nI was more looking for a simple explanation. When you look at the\nplots, these straight lines are not some vague approximation that you\ncan only see if you close your eyes so small slits. The points (with\nvery small error bars) are reall spot on! So I cannot believe that\nthey are just some strong coupling coincidence they cry for a simple\nexplanation.\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, 27 May 2004 09:47:36 -0400, Lubos Motl <motl@feynman.harvard.edu> wrote:
> Otherwise these stringy QCD effects are seen in numerical/lattice
> calculations, too, but the real QCD is not a great approximation of
> perturbative string theory in a mildly curved space because 3 from SU(3)
> is not quite infinity, although it is close (if counted by 1/N).
The lattice calculations show that QCD contains Regge trajectories but
I was more looking for a simple explanation. When you look at the
plots, these straight lines are not some vague approximation that you
can only see if you close your eyes so small slits. The points (with
very small error bars) are reall spot on! So I cannot believe that
they are just some strong coupling coincidence they cry for a simple
explanation.
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
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