Topological fluctuations in dense matter with two colors

We study the topological charge fluctuations of an SU(2) lattice gauge theory containing both Nf=2 and 4 flavors of Wilson fermion, at low temperature with non-zero chemical potential μ. The topological susceptibility, χT, is used to characterise differing physical regimes as μ is varied between the onset of matter at μo and color deconfinement at μd. Suppression of instantons by matter via Debye screening is also investigated, revealing effects not captured by perturbative predictions. In particular, the breaking of scale invariance leads to the mean instanton size ρ¯ becoming μ-dependent in the regime between onset and deconfinement, with a scaling ρ¯∝μ−2 over the range μo<μ<μd, resulting in an enhancement of χT immediately above onset.