Towards a determination of the chiral critical surface of QCD

Understand

The chiral critical surface is a surface of second order phase transitions bounding the region of first order chiral phase transitions for small quark masses in the {m_{u,d}, m_s,\mu} parameter space.

• The potential critical endpoint of the QCD (T,\mu)-phase diagram is widely expected to be part of this surface.
• Since for \mu=0 with physical quark masses QCD is known to exhibit an analytic crossover, this expectation requires the region of chiral transitions to expand with \mu for a chiral critical endpoint to exist.
• Instead, on coarse N_t=4 lattices, we find the area of chiral transitions to shrink with \mu, which excludes a chiral critical point for QCD at moderate chemical potentials \mu_B < 500 MeV.