Topology of two-color QCD at low temperature and high density

The chemical potential ($\mu$) dependence of the topological susceptibility with two-color two-flavor QCD is studied. We find that at temperature $T \approx T_c /2$, where $T_c$ denotes the critical temperature at zero chemical potential, the topological susceptibility is almost constant throughout $0 \leq a\mu \lesssim 1.0$, while at $T\approx T_c$, it decreases significantly from the $\mu=0$ value in a high $\mu$ regime. In this work, we perform the simulation for $\mu/T \le 16$, which covers even the low temperature and the high chemical potential regime. In this regime, we introduce a diquark source term, which is characterized by $j$, into the action. We also show our results for the phase diagram in a low temperature regime ($T\approx T_c/2$), which is obtained after taking the $j \to 0$ limit of the diquark condensate and the Polyakov loop.