Electric conductivity in finite-density SU(2) lattice gauge theory with dynamical fermions

We study the dependence of the electric conductivity on chemical potential in finite-density SU(2) gauge theory with N-f = 2 flavors of rooted staggered sea quarks, in combination with Wilson-Dirac and domain-wall valence quarks. The pion mass is reasonably small with m(pi)/m(rho) approximate to 0.4. We concentrate in particular on the vicinity of the chiral crossover, where we find the low-frequency electric conductivity to be most sensitive to small changes in fermion density. Working in the low-density QCD-like regime with spontaneously broken chiral symmetry, we obtain an estimate of the first nontrivial coefficient coTTHORN of the expansion of conductivity sigma(T, mu) = sigma(T, 0)(1 + c(T)(mu/T)(2) + O(mu(4))) in powers of mu, which has rather weak temperature dependence and takes its maximal value c(T) approximate to 0.10 +/- 0.07 around the critical temperature. At larger densities and lower temperatures, the conductivity quickly grows toward the diquark condensation phase and also becomes closer to the free-quark result. As a by-product of our study we confirm the conclusions of previous studies with heavier pion that for SU(2) gauge theory the ratio of crossover temperature to pion mass T-c/m(pi) approximate to 0.4 at mu = 0 is significantly smaller than in real QCD.