Tetracritical behavior in strongly interacting theories

We suggest a tetracritical fixed point to naturally occur in strongly interacting theories. As a fundamental example we analyze the temperature-quark chemical potential phase diagram of QCD with fermions in the adjoint representation of the gauge group (i.e., adjoint QCD). Here we show that such a nontrivial multicritical point exists and is due to the interplay between the spontaneous breaking of a global [Formula Presented] symmetry and the center group symmetry associated with confinement. Our results demonstrate that taking confinement into account is essential for understanding the critical behavior as well as the full structure of the phase diagram of adjoint QCD. This is in contrast to ordinary QCD where the center group symmetry associated with confinement is explicitly broken when the quarks are part of the theory. © 2004 The American Physical Society.