The problem of repulsive quark interactions - Lattice versus mean field models

TL;DR

This paper compares lattice data with models including quark and hadronic degrees of freedom to understand quark interactions, finding that repulsive vector interactions are unlikely above the critical temperature.

Contribution

It introduces a combined quark-hadron model and analyzes quark susceptibilities to constrain the nature of quark interactions near the phase transition.

Findings

Susceptibilities are highly sensitive to quark-quark vector interactions.

Repulsive vector interactions above T_c are excluded by lattice data.

Best fit to lattice data near T_c involves coexistence of hadronic and quark degrees of freedom.

Abstract

We calculate the 2nd and 4th order quark number susceptibilities at zero baryochemical potential, using a PNJL approach and an approach which includes, in a single model, quark and hadronic degrees of freedom. We observe that the susceptibilities are very sensitive to possible quark-quark vector interactions. Compared to lattice data our results suggest that above $T_c$ any mean field type of repulsive vector interaction can be excluded from model calculations. Below $T_c$ our results show only very weak sensitivity on the strength of the quark and hadronic vector interaction. The best description of lattice data around $T_c$ is obtained for a case of coexistence of hadronic and quark degrees of freedom.