Speaker
Description
We present a phase diagram study of the O(4) model as an effective
theory for 2-flavor QCD. Both theories perform spontaneous symmetry
breaking with isomorphic groups, which suggests that they
belong to the same universality class. Since we are interested
in high temperature, we further assume dimensional reduction
to the 3d O(4) model, which implies topological sectors.
As conjectured by Skyrme and others, this topological charge
represents the baryon number. Hence the baryon chemical
potential mu_B appears as an imaginary vacuum angle, which can
be included in the lattice simulation without any sign problem.
We present numerical results for the critical line in the chiral
limit, and for the cross-over in the presence of light quark masses.
The shapes of these lines are compatible with other predictions, but
up to about mu_B = 300 MeV we did not find a Critical Endpoint,
although there are indications that it could be near-by.
