Numerical Study of Dense Adjoint Matter in Two Color QCD

TL;DR

This study explores the phase structure and symmetry breaking in two-color QCD with adjoint fermions at finite density, using numerical simulations that compare algorithms and validate theoretical predictions.

Contribution

It provides the first numerical analysis of SU(2) lattice gauge theory with adjoint fermions at finite density, highlighting algorithmic differences and symmetry breaking patterns.

Findings

TSMB maintains ergodicity in dense phases.

HMC results agree with chiral perturbation theory for N>=2.

Sign of fermion determinant influences the onset of dense matter.

Abstract

We identify the global symmetries of SU(2) lattice gauge theory with N flavors of staggered fermion in the presence of a quark chemical potential mu, for fermions in both fundamental and adjoint representations, and anticipate likely patterns of symmetry breaking at both low and high densities. Results from numerical simulations of the model with N=1 adjoint flavor on a 4^3x8 lattice are presented, using both hybrid Monte Carlo and Two-Step Multi-Boson algorithms. It is shown that the sign of the fermion determinant starts to fluctuate once the model enters a phase with non-zero baryon charge density. HMC simulations are not ergodic in this regime, but TSMB simulations retain ergodicity even in the dense phase, and in addition appear to show superior decorrelation. The HMC results for the equation of state and the pion mass show good quantitative agreement with the predictions of chiral perturbation theory, which should hold only for N>=2. The TSMB results incorporating the sign of the determinant support a delayed onset transition, consistent with the pattern of symmetry breaking expected for N=1.