Tricritical scaling at the N_t=6 chiral phase transition for 2 flavour lattice QCD with staggered quarks

TL;DR

This study investigates the nature of the chiral phase transition in 2-flavor lattice QCD with staggered quarks at N_t=6, revealing tricritical scaling behavior through simulations with added four-fermion interactions.

Contribution

The paper demonstrates that the chiral phase transition at N_t=6 exhibits tricritical scaling, challenging the expected universality class predictions for this lattice QCD setup.

Findings

The transition is second order with tricritical exponents.

Chiral symmetry is restored above the transition.

Pion screening mass vanishes below the transition.

Abstract

We have simulated lattice QCD directly in the chiral limit of zero quark mass by adding an additional, irrelevant 4-fermion interaction to the standard action. Using lattices having temporal extent of six and spatial extents of twelve and eighteen, we find that the theory with 2 massless staggered quark flavors has a second order finite temperature phase transition. The critical exponents $\beta_{mag}$, $\delta$ and $\nu$ are measured and favour tricritical behaviour over that expected by universality arguments. The pion screening mass is consistent with zero below the transition, but is degenerate with the nonzero $\sigma(f_0)$ mass above the transition, indicating the restoration of chiral symmetry.