2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/214480The infrared problem of the effective action in 2D is discussed in the framework of the Covariant Perturbation Theory. The divergences are regularised by a mass and the leading term is evaluated up to the third order of perturbation theory. A summation scheme is proposed which isolates the divergences from the finite part of the series and results in a single term. The latter turns out to be equivalent to the coupling to a certain classical external field. This suggests a renormalisation by factorisation.25 pagesGeneral Relativity and Quantum Cosmologytext