Phases ofN=∞QCD-like gauge theories onS3×S1and nonperturbative orbifold-orientifold equivalences

Abstract

We study the phase diagrams of $N=\ensuremath{\infty}$ vectorlike, asymptotically free gauge theories as a function of volume, on ${S}^{3}\ifmmode\times\else\texttimes\fi{}{S}^{1}$. The theories of interest are the ones with fermions in two index representations [adjoint, (anti)symmetric, and bifundamental abbreviated as QCD(adj), QCD(AS/S), and QCD(BF)], and are interrelated via orbifold or orientifold projections. The phase diagrams reveal interesting phenomena such as disentangled realizations of chiral and center symmetry, confinement without chiral symmetry breaking, zero temperature chiral transitions, and in some cases, exotic phases which spontaneously break the discrete symmetries such as $C$, $P$, $T$ as well as $CPT$. In a regime where the theories are perturbative, the deconfinement temperature in SYM, and QCD(AS/S/BF) coincide. The thermal phase diagrams of thermal orbifold QCD(BF), orientifold QCD(AS/S), and $\mathcal{N}=1$ SYM coincide, provided charge conjugation symmetry for QCD(AS/S) and ${\mathbb{Z}}_{2}$ interchange symmetry of the QCD(BF) are not broken in the phase continuously connected to the ${\mathbb{R}}^{4}$ limit. When the ${S}^{1}$ circle is endowed with periodic boundary conditions, the (nonthermal) phase diagrams of orbifold and orientifold QCD are still the same, however, both theories possess chirally symmetric phases which are absent in $\mathcal{N}=1$ SYM. The match and mismatch of the phase diagrams depending on the spin structure of fermions along the ${S}^{1}$ circle is naturally explained in terms of the necessary and sufficient symmetry realization conditions which determine the validity of the nonperturbative orbifold-orientifold equivalence.