  We present unambiguous evidence from lattice simulations of QCD with three
degenerate quark species for two tricritical points in the (T,m) phase diagram
at fixed imaginary \mu/T=i\pi/3 mod 2\pi/3, one in the light and one in the
heavy mass regime. These represent the boundaries of the chiral and
deconfinement critical lines continued to imaginary chemical potential,
respectively. It is demonstrated that the shape of the deconfinement critical
line for real chemical potentials is dictated by tricritical scaling and
implies the weakening of the deconfinement transition with real chemical
potential. The generalization to non-degenerate and light quark masses is
discussed.
