Numerical study of dense adjoint matter in two color QCD

We identify the global symmetries of SU(2) lattice gauge theory with N flav ors of staggered fermion in the presence of a quark chemical potential mu, for fermions in both fundamental and adjoint representations, and anticipat e likely patterns of symmetry breaking at both low and high densities. Resu lts from numerical simulations of the model with N = 1 adjoint flavor on a 4(3) x 8 lattice are presented, using both hybrid Monte Carlo and Two-Step Multi-Boson algorithms. It is shown that the sign of the fermion determinan t starts to fluctuate once the model enters a phase with non-zero baryon ch arge density. HMC simulations are not ergodic in this regime, but TSMB simu lations retain ergodicity even in the dense phase, and in addition appear t o show superior decorrelation. The HMC results for the equation of state an d the pion mass show good quantitative agreement with the predictions of ch iral perturbation theory, which should hold only for N greater than or equa l to 2. The TSMB results incorporating the sign of the determinant support a delayed onset transition, consistent with the pattern of symmetry breakin g expected for N = 1.