2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/51380The simple consequences of the renormalization group invariance in calculations of the ground state energy for models of confined quantum fields are discussed. The case of (1+1)D MIT quark bag model is considered in detail.Talk at the conference Renormalization Group 2002 (March 10-16, High Tatras, Slovakia). 4 pages, LaTeXHigh Energy Physics - Theorytext