tag:blogger.com,1999:blog-8666091.post4383167701953383794..comments2021-02-05T18:38:25.974+01:00Comments on The Reference Frame: Guest blog: on applications of holographyLuboš Motlhttp://www.blogger.com/profile/17487263983247488359noreply@blogger.comBlogger19125tag:blogger.com,1999:blog-8666091.post-68214394606477913102014-06-18T06:57:16.322+02:002014-06-18T06:57:16.322+02:00We are the manufacturer, supplier, trader and expo...We are the manufacturer, supplier, trader and exporter of scientific educational laboratory equipment and instruments including physics, chemistry lab equipment <a href="http://www.aticoexport.com/" rel="nofollow"> click more</a>seoaticonoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-24577294113084243672014-04-02T11:08:06.068+02:002014-04-02T11:08:06.068+02:00PLAN DETAILS ::
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At the same time, over the last ten years I've developed an enormous appreciation for both the insights and the many 'applications' coming from AdS/CFT, so I also agree with Andreas in thinking that there is still a lot of perhaps not fundamental but nonetheless interesting applications to be pursued.W.A. Zajcnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-18531204054511243522013-09-26T15:28:29.634+02:002013-09-26T15:28:29.634+02:00Thanks, Andreas, your point it appreciated here. T...Thanks, Andreas, your point it appreciated here. The peak of the research rate in the stringy unification may look "earlier" than the AdS/applications research.<br /><br /><br />But I would guess that you will be proven wrong and in the next 10 years, it will be the big picture of ST that will show some new progress, perhaps experimentally inspired.Luboš Motlhttp://motls.blogspot.com/noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-10946527454994419412013-09-26T15:02:16.581+02:002013-09-26T15:02:16.581+02:00Yeah, Andreas doesn't disagree with you on thi...Yeah, Andreas doesn't disagree with you on this Lubos. But as a researcher you have to decide what topic is interesting AND ripe for progress. I see a lot of interesting things to come out of AdS studies in the next 10 years. Strings and unification - not sure how much we currently have to add over the 80s and 90s.Andreas Karchnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-54194903016194453892013-09-26T07:05:59.608+02:002013-09-26T07:05:59.608+02:00Dear Bill, it was mostly my typo created during Te...Dear Bill, it was mostly my typo created during TeXification. There was no parenthesis and in the text form, with the extra space, it looked like multiplication. Of course I know that the right constant is 1/(4 pi).Luboš Motlhttp://motls.blogspot.com/noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-88734077201409042302013-09-25T23:41:06.813+02:002013-09-25T23:41:06.813+02:00Andreas, thanks for your very nice guest post, eve...Andreas, thanks for your very nice guest post, even if it is largely devoted to what our host very recently described as "some - already not too important - problems of the quark-gluon plasma" ;-) I also enjoyed the slides and proceedings you provided as links. <br /><br />There is trivial typo in your value for the KSS 'bound'; which I know you know is 1/(4 pi). For those who don't think about this every day I would add that this value is in natural units where hbar and Boltzman's constant are both 1; the magic of the KSS result is that even though both the viscosity and the entropy density are calculated in a stringy theory, in the ratio there are no factors of Newton's constant or the speed of light or the string tension or anything else.<br /><br />I was amused when you noted that the press release announcing the discovery of the (near) "perfect liquid" incorrectly highlights the small value of the viscosity of QGP, rather than the quantity which is indeed small, the ratio of viscosity to entropy density. I participated in the group that drafted the press release, but was not able to get this fine distinction clarified. If I recall correctly, I believe the counter-arguments were that no one would know what entropy density is, and that engineers routinely tabulate kinematic viscosity (viscosity divided by mass density), so what were talking about is something a relativistic version of kinematic viscosity; let's just call it viscosity. (On the other hand, I was able to get the reference to string theory in the release.)<br /><br />I also struggled with this issue in two other pieces even when I had more control over the content. The first was an item I wrote on Nuclear Physics Highlights for the Department of Energy http://science.energy.gov/~/media/np/pdf/docs/nph_basicversion_std_res.pdf where (with some back and forth with the editors) I called it "the ratio of viscosity to the thermal density, or entropy". Well, this is technically wrong, 'density' should follow 'entropy', but I guess I'm in good company as the same is true in your post ;-). In the Scientific American article I wrote with Michael Riordan (http://www.scientificamerican.com/article.cfm?id=the-first-few-microsecond-2006-05 , yes, there is a paywall), we referred to the viscosity to entropy density ratio as "specific viscosity", which I think is a useful nomenclature. <br /><br />Again, thanks for your detailed and interesting discussion!W.A. Zajcnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-32465423818587828552013-09-25T20:02:21.979+02:002013-09-25T20:02:21.979+02:00Thanks Andreas Karch,
As the connection between b...Thanks Andreas Karch,<br /><br /><i>As the connection between black holes and heavy-ion physics is more qualitative than quantitative, I would not go so far as to say we can use heavy-ion physics to learn about black holes.</i><br /><br />I was attracted to statements like, "<i>When two particles hit dead-on at close to light speed, a small amount of energy greatly concentrates into a tiny space.</i> Do you see this then as more then just a qualitative look by using experimnt to focus in that space of QGP materialization and the after affects of particle decay?<br /><br /><br />I guess as laymen, I would want to know if it is okay to say QGP is in fact, the first evdience of microscopic black hole creation?<br /><br /><i>Physicists know that it should take a certain amount of energy—more than the LHC could ever conjure—to make a microscopic black hole. But if gravity is stronger than we think, then the threshold of energy needed could be within range of both the LHC and cosmic-ray collisions with Earth’s atmosphere, says theoretical physicist Steve Giddings from the University of California, Santa Barbara.</i><b>See</b>:<a href="http://www.symmetrymagazine.org/article/september-2013/the-hunt-for-microscopic-black-holes" rel="nofollow">The hunt for microscopic black holes</a>PlatoHagelhttp://www.eskesthai.com/noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-32655511742445407172013-09-25T18:34:13.621+02:002013-09-25T18:34:13.621+02:00Yes, many thanks for the guest blog... too technic...Yes, many thanks for the guest blog... too technical for me to follow much, but I use Penrose's suggestion to skim the material anyway--like learning a language.Gordonnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-79211577923405939122013-09-25T18:29:46.526+02:002013-09-25T18:29:46.526+02:00Thanks again for the feedback.
Olena:
1) In theor...Thanks again for the feedback.<br />Olena: <br />1) In theories with good (supergravity) holographic dual the ratio of the two masses of lightest spin 2 and spin 1 mesons is lambda^(1/4) where lambda is a large parameter. Corrections to SUGRA go as 1/lambda^(1/2). Maybe one can hope that (1.5)^2 is a large number and so a gravity dual to QCD is not entirely unreasonable, but it's certainly not large enough to think of it as a systematic approximation.<br />2) To solve QCD holographically we need to understand quantum string theory. To solve large N QCD, we indeed only need classical string theory - meaning no string loops. In practice, this still means you need to understand the 2d QFT living on the string worldsheet (classical string theory then means that you only need to study this 2d theory on the sphere, no need to sum over topologies). For strings in flat space, that 2d theory is free and you can find everything there is to know about it in textbooks. For the kind of backgrounds that appear in holography, that 2d theory so far has proven to be untractable.<br />Dilaton: look at the recent papers by Paul Chesler. He and his collaborators find numerical gravity solutions to turbulent flows, both in normal as well as superfluids. In turbulent flows energy cascades from large to small scales (or vice versa, depending on the dimension). The advantage holographic models have over purely hydrodynamic simulations is that holography is a complete description, including short distance scales. It knows exactly how the energy in eddies eventually dissipates. Their paper on superfluids is one of the very few string theory papers that ever made it into SCIENCE.Andreas Karchnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-13660062437259247592013-09-25T17:03:14.293+02:002013-09-25T17:03:14.293+02:00*inaccessible*inaccessibleAnonnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-54997187137581622372013-09-25T15:43:07.928+02:002013-09-25T15:43:07.928+02:00Thanks for this very nice, interesting article :-)...Thanks for this very nice, interesting article :-)!<br /><br />The introductery remarks above are nicely adding to the answers of a question I once had on Physics SE<br /><br />http://physics.stackexchange.com/q/69034/2751<br /><br />because I was confused by the fact that some people said that supergravity is the holographic gravity dual in AdS/something and others said it is string theory ...<br /><br /><br />Concerning applications to fluid dynamics of more specifically turbulence: Do you think it is possible to obtain a turbulent diffusion paramterization from holographic considerations? I have quite some time ago seen some PowerPoint slides of Johanna Erdmenger, where she some kind of calculated a turbulent diffusion coefficient from gravity. But I did not save the file and now I can no longer find it :-/. Do you have some good references about this?<br /><br /><br />The comment concerning new phases found exclusively by applying holography is interesting too. Does this mean that with holographic methods one can find new (IR) fixed points of a system, that are not (easy) detectable when doing "ordinary" renormalization group flow calculations?<br /><br /><br />In case I mix up and misunderstand things too much, I apologize ...Dilatonnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-80208033446122270272013-09-25T10:13:50.304+02:002013-09-25T10:13:50.304+02:00Thanks, Andreas. Can you please clarify the follow...Thanks, Andreas. Can you please clarify the following basics for me?<br /><br />"The lightest spin 2 and spin 1 mesons come in at 1275 MeV and 750 MeV respectively."<br /><br />So the spin 1 meson *is* lighter than the spin 2 meson. How much lighter would it have to be for a gravitational dual (in the usual sense) to exist?<br /><br />"If we could study even classical string theory on AdS space, large N QCD would be solved."<br /><br /><br /><br />What's hard about classical string theory? Surely you mean we'd have to solve the quantum string theory and study the right classical limit of it. If that's correct, what is difficult, identifying the right string background or taking the correct classical limit, or both?<br /><br /><br />Best, OlenaOlena Olbychevanoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-53399913040470953292013-09-25T08:29:32.903+02:002013-09-25T08:29:32.903+02:00Schönen Gruss aus Luxemburg! Wir waren vor 15 Jahr...Schönen Gruss aus Luxemburg! Wir waren vor 15 Jahren mal gemeinsam auf einer Konferenz in Corfu. Freut mich, dass Du der Physik treu geblieben bist.Tom Weidignoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-82046290879081677242013-09-25T07:56:11.186+02:002013-09-25T07:56:11.186+02:00Thank you very much, Andreas, for this review writ...Thank you very much, Andreas, for this review written with the hindsight you may afford now.Luboš Motlhttp://motls.blogspot.com/noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-34480528713982877882013-09-24T23:49:53.124+02:002013-09-24T23:49:53.124+02:00Thanks for the feedback.
NumCracker:
1) ima...Thanks for the feedback.<br /><br /><br />NumCracker: <br /><br /><br /><br />1) imaginary chemical potential is not the same as real chemical potential. One can try to analytically continue back to real chemical potential, but that is only reliable at extremely small chemical potential, mu << T. The most interesting questions (like whether there is a QCD critical point in nature) are not answered by this approach.<br /><br /><br />2) If you call "the most straightforward" way a model which has, according to the abstract "two set of parameters" to fit the RHIC data, I think this is a really low hanging fruit. Yes, I agree that the data we have is not enough to completely pin down what is going on. This is not holography's problem - heavy ion collisions are messy. Modified power laws work quite well (see 1305.6458). But ok, so do other thinks.<br /><br /><br /><br />Giotis: Vasilev Gravity is surely not enough to capture small lambda holography. If you look at the degrees of freedom in Vasilev gravity, they are not enough to give you strings. They just account for the string endpoints, not the actual string. This is because you are studying a vector model instead of a matrix model. The gauge invariant operators are QQ instead of QXXXXXXXX........XXXQ where Q is fundamental and X is adjoint. So you would first have to find the right higher spin dual to free SYM (involving and infinite number of Vasilev-like theories interacting with each other) and then try to break higher spin gauge invariance. I don't think anyone has any idea how to do this, even though the idea has certainly been around.<br /><br /><br />PlatoHagel: If we were to do heavy ion-collisions in a world which is governed by a gauge theory with a holographic dual, you could indeed say that we learned something about black holes. While being able to describe the collision in terms of the field theory, we would know there is an equivalent, better description in terms of a black hole. But in our world, I am not so sure. We know that if QCD has a dual, it's a quantum string theory on a highly curved background. And yes, we then can say we learned something about black holes in that theory. But would we still recognize what we see as a black hole? As the connection between black holes and heavy-ion physics is more qualitative than quantitative, I would not go so far as to say we can use heavy-ion physics to learn about black holes.Andreas Karchnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-9636340433006874452013-09-24T21:44:17.349+02:002013-09-24T21:44:17.349+02:00A fascinating post, thanks Adreas!
Still, just fo...A fascinating post, thanks Adreas!<br /><br />Still, just for the sake of accuracy, I would like to comment that<br /><br />(I) "(...) So are even static problems in which we turn on a finite density for fermions, which also leads to a complex weight even in equilibrium (...)"<br /><br />Well, even in such situations LQCD is rescued by reweighting techniques and so called imaginary chemical potential. So, lattice simulations are still the first choice on nearly-extreme conditions when one needs quantitative predictions to fit data.<br /><br />(II) "Energy Loss/Far from equilibrium physics"<br /><br />Still a hard task. But, the most straightforward way here to conciliate usual QCD Blast-Wave models to experiments comes from a simple generalization of BG statistics ( http://xxx.lanl.gov/abs/0812.1609 ).NumCrackernoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-47971759429882165192013-09-24T21:42:28.651+02:002013-09-24T21:42:28.651+02:00Thanks for this nice post.
Regarding the large ’...Thanks for this nice post. <br /><br />Regarding the large ’t Hooft coupling has anyone tried with some broken enough phase of Vasiliev’s Higher<br />Spin Gravity in the bulk? I know that these theories are very hard to handle and people still don’t know that much about them but I was just wondering if such an approach was even considered.Giotisnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-1263605770998617192013-09-24T20:55:28.608+02:002013-09-24T20:55:28.608+02:00Andreas Karch,
Thank you very much for this upda...Andreas Karch,<br /><br /><br />Thank you very much for this update.<br /><br /><br />If the qgp is attributed to a location in the collision process(cosmic particle collisions), how would decay products be derived?<br /><br /><br />So, the microscopic blackhole while quickly dissipating, leaves an energy valuation representing decays products from the collision itself. Would we not say that we have to a degree understood something about microscopic black hole creation in concert with QGP science?PlatoHagelhttp://www.eskesthai.com/noreply@blogger.com