Towards the chiral critical surface of QCD

Understand

The critical endpoint of the QCD phase diagram is usually expected to belong to the chiral critical surface, i.e.

• the surface of second order transitions bounding the region of first order chiral phase transitions for small quark masses in the {m_{u,d}, m_s,\mu} parameter space.
• For \mu=0, QCD with physical quark masses is known to be an analytic crossover, requiring the region of chiral transitions to expand with \mu for a 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.