Phase diagram of dense two-color QCD within lattice simulations

V.V Braguta,A.V Molochkov,A.Yu Kotov,E.-M Ilgenfritz,A.A Nikolaev

doi:10.1051/epjconf/201713707011

Abstract

We present the results of a low-temperature scan of the phase diagram of dense two-color QCD with Nf = 2 quarks. The study is conducted using lattice simulation with rooted staggered quarks. At small chemical potential we observe the hadronic phase, where the theory is in a confining state, chiral symmetry is broken, the baryon density is zero and there is no diquark condensate. At the critical point μ = mπ /2 we observe the expected second order transition to Bose-Einstein condensation of scalar diquarks. In this phase the system is still in confinement in conjunction with nonzero baryon density, but the chiral symmetry is restored in the chiral limit. We have also found that in the first two phases the system is well described by chiral perturbation theory. For larger values of the chemical potential the system turns into another phase, where the relevant degrees of freedom are fermions residing inside the Fermi sphere, and the diquark condensation takes place on the Fermi surface. In this phase the system is still in confinement, chiral symmetry is restored and the system is very similar to the quarkyonic state predicted by SU (Nc ) theory at large Nc .

Highlights

The phase diagram of QCD is of high importance for several fields of observational physics like cosmology and astrophysics
Such experiments are addressing the structure of the phase diagram, the understanding and modeling of an actual collision requires much more than the knowledge of the equilibrium phase diagram
A two-color world differs from the tree-color world, lattice study of QC2D with chemical potential can provide us with important information about the properties of QCD with non-zero baryon density (EoS, generation of the fermion mass gap, etc.)

Summary

Introduction

The phase diagram of QCD is of high importance for several fields of observational physics like cosmology and astrophysics. The properties of QC2D were studied theoretically within the following approaches: ChPT [2,3,4], the NJL model [5,6,7], FRG [8, 9], random matrix theory [10,11,12] These studies have revealed the following phase structure of low temperature QC2D with three subsequent phases: (1) 0 < μ < μc (hadronic phase), (2) μc < μ < μd (“baryon onset” with a superfluid condensate due to Bose-Einstein condensation [BEC]) and (3) μd < μ (the phase with diquark condensation due to the Bardeen-Cooper-Schrieffer mechanism [BCS] [13]). In this paper we are going to study the QC2D phase diagram with N f = 2 flavors going back to the lattice simulation of staggered fermions using the rooting procedure. In the present paper we are going to carry out a μ1 scan at low temperature of the QC2D phase diagram

The lattice set-up

The diquark condensate

The chiral condensate

The baryon density

The gluon observables

Discussion and conclusion