Some Exact Results in QCD-like Theories

Abstract

I propose a controlled approximation to QCD-like theories with massless quarks by employing supersymmetric QCD perturbed by anomaly-mediated supersymmetry breaking. They have identical massless particle contents. Thanks to the ultraviolet insensitivity of anomaly mediation, dynamics can be worked out exactly when m Λ, where m is the size of supersymmetry breaking and Λ the dynamical scale of the gauge theory. I demonstrate that chiral symmetry is dynamically broken for Nf≤32Nc while the theories lead to nontrivial infrared fixed points for larger number of flavors. While there may be a phase transition as m is increased beyond Λ, qualitative agreements with expectations in QCD are encouraging and suggest that two limits m Λ and m≫Λ may be in the same universality class.