The chiral phase transition for two-flavour QCD at imaginary and zero chemical potential

Understand

The chiral symmetry of QCD with two massless quark flavours gets restored in a non-analytic chiral phase transition at finite temperature and zero density.

• Whether this is a first-order or a second-order transition has not yet been determined unambiguously, due to the difficulties of simulating light quarks.
• We investigate the nature of the chiral transition as a function of quark mass and imaginary chemical potential, using staggered fermions on N_t=4 lattices.
• At sufficiently large imaginary chemical potential, a clear signal for a first-order transition is obtained for small masses, which weakens with decreasing imaginary chemical potential.