The N_t=4 finite temperature phase transition for lattice QCD with a   weak chiral 4-fermion interaction
  We study the finite temperature phase transition of lattice QCD with an irrelevant chiral 4-fermion interaction and two massless quark flavours, on $8^3 \times 4$ and $12^2 \times 24 \times 4$ lattices. The strength of the 4-fermion interaction was reduced to half the minimum value used in previous simulations, to study how the nature of this phase transition depends on this additional interaction. We find that the transition remains first order as the 4-fermion coupling is reduced. Extending our earlier studies indicates that for sufficiently large 4-fermion coupling, the transition is probably second order. 
J. B. Kogut and D. K. Sinclair