arivero has http://www.physcomments.org/node/444" [Broken] the considerable interest the physics community is showing into the new, or revived, field of Ads/QFT model building. It is somewhat similar to Lisa Randall's style of model building, described in her new book(adsbygoogle = window.adsbygoogle || []).push({}); Warped Passages, which I recommend.

arivero only mentions by name one of the papers fueling the excitement, but I followed it up on the arxiv; it's hep-ph/0501128,

QCD and Holographic Model of Hadrons

By Joshua Erlich, Emanuel Katz, Dam T. Son, and Mikhail A. Stephanov

From the Abstract

From the introduction We propose a five-dimensional framework for modeling low-energy properties of QCD. In the simplest three parameter model we compute masses, decay rates and couplings of the lightest mesons.

The model fits experimental data to within 10%. The framework is a holographic version of the QCD sum rules, motivated by the anti-de Sitter/conformal field theory (AdS/CFT) correspondence. The model naturally incorporates properties of QCD dictated by chiral symmetry, which we demonstrate by deriving the Gell-Mann–Oakes–Renner relationship for the pion mass.

From the Discussion and Outlook Inspired by the gravity/gauge duality we propose the

following complementary approach. Rather than deform

the SYM theory to obtain QCD [5], we start from QCD

and attempt to construct its five-dimensional (5D) holo-

graphic dual. In this Letter, we present an exploratory

study of a simple holographic model of QCD. The field

content of the 5D theory is chosen to reproduce holo-

graphically the dynamics of chiral symmetry breaking in

QCD, the boundary theory. The model has four free pa-

rameters, one of which is fixed by the number of colors;

the remaining three parameters can be fitted using three

well-measured observables, e.g., the ρ meson mass, the

pion mass, and the pion decay constant. The model then

predicts other low-energy hadronic observables with sur-

prisingly good accuracy.

One of the things I liked about this model is that it doesn't require supersymmetry; it just does QCD as we know it (slightly simplified). Do go and look at their tables of fits. Of course the point is not that they can tune a model to fit the data; it is that THIS model, though parsimonious, can be so tuned. It deserves the excited attention it is getting! The holographic model of

QCD studied here is quite crude and depends on only

three free parameters, but it agrees surprisingly well with

the seven experimentally measured observables which we

have studied.

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# The Excitement in AdS/QFT

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