Sensitivity of finite size effects to the boundary conditions and the vacuum term

TL;DR

This study investigates how finite size effects influence phase transition features in a quark-meson model, highlighting the importance of boundary conditions and vacuum term treatment on the critical endpoint and fluctuations.

Contribution

It provides a comparative analysis of finite size effects using momentum cutoff and discretization, emphasizing the impact of boundary conditions and vacuum treatment on phase diagram features.

Findings

CEP shifts to lower temperatures with decreasing system size

Boundary conditions significantly alter the CEP trajectory

Baryon fluctuation measures depend on temperature and chemical potential

Abstract

Finite volume effects are studied both with low-momentum cutoff and with momentum discretization in the framework of an (axial)vector meson extended quark-meson model with Polyakov-loop variables. In the momentum cutoff scenario, the CEP moves to lower temperatures and larger quark chemical potentials as the characteristic system size is reduced, however, the treatment of the vacuum term significantly affects its trajectory. The size dependence of the baryon fluctuations is also studied by the kurtosis and the skewness, both of which show moderate dependence on temperature and some dependence on quark chemical potential. The order of the phase transition is also studied near the chiral limit at finite system size and found to be second-order only at vanishing explicit breaking. The implementation of the finite size effect with momentum discretization is more complicated and shows peculiar behavior due to the different modes dropping below the Fermi surface and strong dependence on the type of the boundary condition chosen. We found that both the different boundary conditions and the treatment of the vacuum term cause significant changes in the trajectory of the CEP as the characteristic system size is changed.