TBA equations for excited states in the O(3) and O(4) nonlinear $σ$-model

2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/184318TBA integral equations are proposed for 1-particle states in the sausage- and SS-models and their $σ$-model limits. Combined with the ground state TBA equations the exact mass gap is computed in the O(3) and O(4) nonlinear $σ$-model and the results are compared to 3-loop perturbation theory and Monte Carlo data.28 pages, 2 eps figures, LaTeX, typo correctedHigh Energy Physics - TheoryHigh Energy Physics - LatticeTBA equations for excited states in the O(3) and O(4) nonlinear $σ$-modeltext