Two-index SU(N) theories from one flavor QCD to Steven Weinberg's ππ scattering legacy

Abstract

I review and improve on how two-index SU(N) gauge-fermion theories help access salient information about the large N vacuum and spectrum of QCD, super Yang Mills and meson-meson scattering. The interplay with recent lattice simulations will be employed to deduce the size of 1/N2 corrections. Through the meson-meson scattering analysis I will honor Steven Weinberg's memory by showing how two-index extrapolations naturally accommodate the appearance of tetraquarks states crucial to unitarize meson-meson scattering at low energies.