Cascading from $\mathscr{N}=2$ Supersymmetric Yang-Mills Theory to Confinement and Chiral Symmetry Breaking in Adjoint QCD
We argue that adjoint QCD in 3+1 dimensions, with any $SU(N)$ gauge group and two Weyl fermion flavors (i.e. one adjoint Dirac fermion), confines and spontaneously breaks its chiral symmetries via the condensation of a fermion bilinear. We flow to this theory from pure $\mathscr{N}=2$ SUSY Yang-Mills theory with the same gauge group, by giving a SUSY-breaking mass $M$ to the scalars in the $\mathscr{N} = 2$ vector multiplet. This flow can be analyzed rigorously at small $M$, where it leads to a deconfined vacuum at the origin of the $\mathscr{N}=2$ Coulomb branch. The analysis can be extended to all $M$ using an Abelian dual description that arises from the $N$ multi-monopole points of the $\mathscr{N} = 2$ theory. At each such point, there are $N-1$ hypermultiplet Higgs fields $h_m^{i = 1, 2}$, which are $SU(2)_R$ doublets. We provide a detailed study of the phase diagram as a function of $M$, by analyzing the semi-classical phases of the dual using a combination of analytic and numerical techniques. The result is a cascade of first-order phase transitions, along which the Higgs fields $h_m^i$ successively turn on, and which interpolates between the Coulomb branch at small $M$, where all $h_m^i = 0$, and a maximal Higgs branch, where all $h_m^i \neq 0$, at sufficiently large $M$. We show that this maximal Higgs branch precisely matches the confining and chiral symmetry breaking phase of two-flavor adjoint QCD, including its broken and unbroken symmetries, its massless spectrum, and the expected large-$N$ scaling of various observables. The spontaneous breaking pattern $SU(2)_R \to U(1)_R$, consistent with the Vafa-Witten theorem, is ensured by an intricate alignment mechanism for the $h_m^i$ in the dual, and leads to a $\mathbb{C}\mathbb{P}^1$ sigma model of increasing radius along the cascade.