2d QCD and Integrability, Part II: Generalized QCD

We extend our study of integrable structures in large Nc QCD₂ to a broad class of theories called the generalized QCD, which are given by the Lagrangian L∝ tr\,B F- tr\,V(B) coupled to quarks in the fundamental representation. We recast the Bethe-Salpeter equation for the meson spectrum into a TQ-Baxter equation and determine a transfer matrix in a closed form for any given polynomial $V(B)$. Using this reformulation, we derive the asymptotic expansion of energy levels and wavefunctions. Examining the analytic structure of the spectrum as a function of the coefficients of $V(B)$, we determine the region of couplings where the theory admits a positive and discrete spectrum of mesons. Furthermore, we uncover a multi-sheeted structure with infinitely many multi-critical points, where several mesons become simultaneously massless. Lastly, we illustrate that this structure persists in the large-representation limit of the generalized QCD with the SU(2) gauge group.