  We employ the linear sigma model to study the chiral dynamics of two flavors
of quarks at finite temperature and density. Our calculations include thermal
fluctuations of both the bosonic and fermionic fields. In particular, we
determine the phase diagram in the plane of temperature and baryon chemical
potential as a function of the pion mass. An interesting phase structure occurs
that results in zero, one, or two critical points depending on the value of the
vacuum pion mass.
