2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/49824In this thesis, we review recent progresses on Nonlinear Integral Equation approach to finite size effects in two dimensional integrable quantum field theories, with emphasis to Sine-Gordon/Massive Thirring model and restrictions to minimal models perturbed by $Φ_{1,3}$. Exact calculations of the dependence of energy levels on the size are presented for vacuum and many excited states.PhD thesis, 96 pages, 28 figuresHigh Energy Physics - Theorytext