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Topological Fluctuations in Dense Matter with Two Colors

We study the topological charge fluctuations of an SU(2) lattice gauge theory containing both N_f=2 and 4 flavors of Wilson fermion, at low temperature with non-zero chemical potential $μ$. The topological susceptibility, chi_T, is used to characterize differing physical regimes as mu is varied between the onset of matter at mu_o and and color deconfinement at mu_d. 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 rho becoming mu-dependent in the regime between onset and deconfinement, with a scaling rho~1/mu^2 over the range mu_o<mu<mu_d, resulting in an enhancement of chi_T immediately above onset.