Net baryon number fluctuations across the chiral phase transition at finite density in the strong coupling lattice QCD

We investigate the net-baryon number fluctuations across the chiral phase transition at finite density in the strong coupling and chiral limit. Mesonic field fluctuations are taken into account by using the auxiliary field Monte-Carlo method. We find that the higher-order cumulant ratios, $S\sigma$ and $\kappa {\sigma }^2$, show oscillatory behavior around the phase boundary at $\mu \mathrm{/}T\gtrsim 0.2$, and there exists the region where the higher-order cumulant ratios are negative. The negative region of $\kappa {\sigma }^2$ is found to shrink with increasing lattice size. This behavior agrees with the expectations from the scaling analysis.