2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/148922The beta function of the vacuum energy density is computed at the four-loop level in massive O(N) symmetric phi^4 theory. Dimensional regularization is used in conjunction with the MSbar scheme and all calculations are in momentum space in the massive theory. The result is beta_v = g N/4+g^3 N(N+2)/96+g^4 N(N+2)(N+8)[12 zeta(3)-25]/1296+o(g^5).16 pages, latex, no figures. Enlarged and updated reference list, minor typographical changesHigh Energy Physics - PhenomenologyStatistical MechanicsHigh Energy Physics - Theorytext