Abstract
We study two-color QCD with two flavors of Wilson fermion as a function of quark chemical potential mu and temperature T, for two different lattice spacings and two different quark masses. We find that the quarkyonic region, where the behaviour of the quark number density and the diquark condensate are described by a Fermi sphere of almost free quarks distorted by a BCS gap, extends to larger chemical potentials with decreasing lattice spacing or quark mass. In both cases, the quark number density also approaches its non-interacting value. The pressure at low temperature is found to approach the Stefan-Boltzmann limit from below.
Highlights
The structure of strongly interacting matter at high densities and low to moderate temperatures remains an outstanding problem, with applications to compact stars, neutron star mergers, and the generation of heavy-ion colliders at FAIR and NICA
We find that the quarkyonic region, where the behavior of the quark number density and the diquark condensate are described by a Fermi sphere of almost free quarks distorted by a Bardeen-Cooper-Schrieffer gap, extends to larger chemical potentials with decreasing lattice spacing or quark mass
First-principles studies of this regime are hindered by the sign problem: with chemical potential μ ≠ 0 the Euclidean action becomes complex, and can not be used as a probability weight in Monte Carlo simulations, which are the mainstay of lattice gauge theory, the method of choice for first-principles, nonperturbative quantum field theory
Summary
The structure of strongly interacting matter at high densities and low to moderate temperatures remains an outstanding problem, with applications to compact stars, neutron star mergers, and the generation of heavy-ion colliders at FAIR and NICA. First-principles studies of this regime are hindered by the sign problem: with chemical potential μ ≠ 0 the Euclidean action becomes complex, and can not be used as a probability weight in Monte Carlo simulations, which are the mainstay of lattice gauge theory, the method of choice for first-principles, nonperturbative quantum field theory. Despite recent progress in alternative sampling approaches such as the density of states method [1], complex Langevin [2] and Lefschetz thimble and related approaches [3,4], we do not as yet have any method that has been shown to yield valid and reliable results for real QCD. The problem may be circumvented by studying QCDlike theories without a sign problem, such as theories with adjoint fermions in any gauge group, QCD with isospin
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