Diquark Condensation at Nonzero Chemical Potential and Temperature

TL;DR

This paper investigates the phase structure of SU(2) lattice gauge theory with four quark flavors at nonzero chemical potential and temperature, revealing a tricritical point and phase transitions via simulations and effective theories.

Contribution

It provides the first evidence of a tricritical point in the $$-$T$ phase diagram of SU(2) gauge theory with four flavors, combining lattice simulations with effective Lagrangian analysis.

Findings

Evidence for a tricritical point in the $$-$T$ plane.

Identification of second order and first order phase transition lines.

Estimation of the tricritical point position using effective Lagrangians.

Abstract

SU(2) lattice gauge theory with four flavors of quarks is studied at nonzero chemical potential $\mu$ and temperature $T$ by computer simulation and Effective Lagrangian techniques. Simulations are done on $8^4$, $8^3 \times 4$ and $12^3 \times 6$ lattices and the diquark condensate, chiral order parameter, Wilson line, fermion energy and number densities are measured. Simulations at a fixed, nonzero quark mass provide evidence for a tricritical point in the $\mu$-$T$ plane associated with diquark condensation. For low $T$, increasing $\mu$ takes the system through a line of second order phase transitions to a diquark condensed phase. Increasing $T$ at high $\mu$, the system passes through a line of first order transitions from the diquark phase to the quark-gluon plasma phase. Using Effective Lagrangians we estimate the position of the tricritical point and ascribe its existence to trilinear couplings that increase with $\mu$ and $T$.