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I am sending a couple of questions which seem a bit more specific than others on this site, partially to probe if there is a point in doing so. Not sure what is the range of expertise here, and no way to find out without trying, so here goes:

I am wondering what is known about QCD, or other field theories, in the regime of large density and low temperatures, specifically studied in the large N limit. I know of the qualitative picture at finite N, but lots of the instabilities (e.g. the superconducting ones) are suppressed at large N and replaced by other interesting phenomena. I am only aware at the moment of the DGR instability to form chiral density waves, and I am wondering what else exists in the vast and possibly quite old literature. Any pointers or entry points to that literature will be appreciated

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  • $\begingroup$ This is quite a general question, but I'm looking forward to some interesting responses. :) $\endgroup$
    – Noldorin
    Commented Jan 12, 2011 at 18:50

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If by large density you mean large baryon density, then I believe one of the fundamental large $N_c$ results is that at densities of order nuclear densities, but below the density where the baryons have dissolved into quarks, baryonic matter forms a crystalline structure. This has been analyzed in the Skyrme model. I think this paper by Klebanov was one of the first to point this out: "Nuclear Matter In The Skyrme Model,"Igor R. Klebanov, Nucl.Phys.B262:133,1985.

AdS/QCD models can also be used to study QCD at large baryon chemical potential and low temperatures (and necessarily at large $N_c$). An instability to the condensation of vector mesons resulting from Chern-Simons couplings dictated by anomaly matching was found in a paper by me and S. Domokos, arXiv:0704.1604. I'm not aware of any evidence that this phenomenon happens in the real world, and even its existence at large $N_c$ should be regarded as conjectural. I don't know whether this instability is related to the DGR instability or not.

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  • $\begingroup$ Thanks, I am aware of your paper, and there are some developments recently on the holographic side (Ooguri and collaborators, and others). I was mostly wondering about small 'tHooft coupling, where it is plausible there is some common wisdom I am not aware of. Indeed, there is, I'll look at the Klebanov paper, thanks. $\endgroup$
    – user566
    Commented Jan 12, 2011 at 19:33