We study two-color QCD with two flavors of Wilson fermion as a function of quark chemical potential µ and temperature T . We find evidence of a superfluid phase at intermediate µ and low T where the quark number density and diquark condensate are both very well described by a Fermi sphere of nearly-free quarks disrupted by a BCS condensate. Our results suggest that the quark contribution to the energy density is negative (and balanced by a positive gauge contribution), although this result is highly sensitive to details of the energy renormalisation. We also find evidence that the chiral condensate in this region vanishes in the massless limit. This region gives way to a region of deconfined quark matter at higher T and µ, with the deconfinement temperature, determined from the renormalised Polyakov loop, decreasing only very slowly with increasing chemical potential. The quark number susceptibility χq does not exhibit any qualitative change at the deconfinement transition. We argue that this is because χq is not an appropriate measure of deconfinement for 2-color QCD at high density.

Abstract. We investigate 2-colour QCD with 2 flavours of Wilson fermion at nonzero temperature T and quark chemical potential µ, with a pion mass of 700 MeV (mπ/mρ = 0.8). From temperature scans at fixed µ we find that the critical temperature for the superfluid to normal transition depends only very weakly on µ above the onset chemical potential, while the deconfinement crossover temperature is clearly decreasing with µ. We find indications of a region of superfluid but deconfined matter at high µ and intermediate T . The static quark potential determined from the Wilson loop is found to exhibit a 'string tension' that increases at large µ in the 'deconfined' region. The electric (longitudinal) gluon propagator in Landau gauge becomes strongly screened with increasing temperature and chemical potential. The magnetic (transverse) gluon shows little sensitivity to temperature, and exhibits a mild enhancement at intermediate µ before becoming suppressed at large µ.PACS. 11.15Ha Lattice gauge theory -12.38Aw Lattice QCD calculations -21.65Qr Quark matter -12.38Mh Quark-gluon plasma

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We study two-color QCD with two flavors of Wilson fermion as a function of quark chemical potential µ and temperature T . We find evidence of a superfluid phase at intermediate µ and low T where the quark number density and diquark condensate are both very well described by a Fermi sphere of nearly-free quarks disrupted by a BCS condensate. This gives way to a region of deconfined quark matter at higher T and µ, with the deconfinement temperature decreasing only very slowly with increasing chemical potential. We find that heavy quarkonium bound states persist in the S-wave channels at all T and µ, with an energy reflecting the phase structure. P-wave states appear not to survive in the quarkyonic region.

I present recent results from lattice simulations of SU(2) gauge theory with N f = 2 Wilson quark flavors, at non-zero quark chemical potential µ. The thermodynamic equation of state is discussed along with the nature of the high density matter which forms. It is conjectured that deconfinement may mean different things for bulk and Fermi surface phenomena.