Scaling behaviour at the $N_t=6$ chiral phase transition for 2-flavour lattice QCD with massless staggered quarks, and an irrelevant 4-fermion interaction

Abstract

We have simulated lattice QCD with 2 flavours of massless staggered quarks. An irrelevant chiral 4-fermion interaction was added to the standard quark action to allow us to simulate at zero quark mass. Thermodynamics was studied on lattices of temporal extent 6. Clear evidence for a second order chiral transition was observed and the critical exponents $β_{mag}$, $δ$, $ν$ and $γ_{mag}$ were measured. These exponents did not agree with those expected by standard universality arguments. They were, however, consistent with tricritical behaviour. The $π$ and $σ$ screening masses were measured and showed clear evidence for chiral symmetry restoration at this transition.