## Gluons are not all the story: An update

In a recent post of mine (see here) I have pointed out to you a beautiful paper by Dan Pirjol and Carlos Schat. This paper is now appeared on Physical Review Letters (see here) but you can find also the preprint on arxiv (see here). I think its content is really important as it gives a serious clue toward our understanding of low-energy QCD. Dan agreed to publish here a contribution about his work and I am glad to post it.

We find that, within experimental errors on the hadron masses, the
so-called gluon-exchange model (OGE) is disfavored by data. This is probably not very  surprising, since at low energies the real degrees of freedom of QCD should include, in addition to the  gluons, also pions (the Goldstone bosons of the spontaneously broken  chiral symmetry). The OGE model does not include the pion exchange effects; an alternative to the OGE model  which includes their effects is the so-called GBE (Goldstone boson exchange) model.

There has been a long-standing debate about the most appropriate model
of quark forces in the framework of the constituent quark model, in  particular about their spin-flavor dependence. The main candidates are
the OGE and GBE models (see e.g. the second paper in Ref.[3] for a
discussion of this controversy). Our letter attempts to resolve this controversy using only minimal assumptions about the orbital dependence
of the hadronic wave functions. More precisely, we assume only isospin
symmetry, but no other assumption is made about the form of the wave
functions. The novel mathematical tool which makes our analysis possible is the application of the permutation group $S_3$, which allows one to study the implications of the most general spin-flavor structure of the quark forces.

### 2 Responses to Gluons are not all the story: An update

1. Daniel de França MTd2 says:

Hi Marco,

http://arxiv.org/abs/0907.1364

QCD Dual
Authors: Francesco Sannino (CP3-Origins)
(Submitted on 9 Jul 2009)

Abstract: We uncover a novel solution of the ‘t Hooft anomaly matching conditions for QCD. Interestingly in the perturbative regime the new gauge theory, if interpreted as a possible QCD dual, predicts the critical number of flavors above which QCD in the nonperturbative regime, develops an infrared stable fixed point. Remarkably this value is identical to the maximum bound predicted in the nonpertubative regime via the all-orders conjectured beta function for nonsupersymmetric gauge theories.

• mfrasca says:

Hi Daniel,

Francesco Sannino is a renowned scientist working in the area of high-energy physics ( http://en.wikipedia.org/wiki/Francesco_Sannino ). Currently, he is working in the University of Southern Denmark but he was born in Italy and got degrees in University of Naples.

His work in QCD is notable for several reasons. He wrote, in collaboration with Thomas Ryttov, an interesting paper published on PRD

http://arxiv.org/abs/0711.3745

where they guess an analytical functional form for the beta function of QCD. They were inspired by a preceding work by Novikov-Shifman-Vainshtein-Zakharov (works of these authors are true cornerstones in our current understanding of QCD) where an analogous result was obtained for the supersymmetric counterpart of QCD. This paper prompted a work by Ding-fang Zeng, also published on PRD, where Sannino and Ryttov’s result was a starting point to evaluate AdS/QCD models ( http://arxiv.org/abs/0805.2733 ).

The paper you cite is indeed relevant as it gives a hint about a possible dual QCD model. A dual QCD model should grant to us an amenable treatment of QCD using perturbation theory. This is a track people is following in the hope to attack the infrared behavior of QCD. My hope is that this track will reach its aims as it would be a consistent verification of whatever else scenario we have for that (mine included). A bonus would be a consistent proof of duality between gravity and gauge theories.

Marco

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