2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/201079We examine backreaction of quantum massive fields on multiply-degenerate (ultraextremal) horizons. It is shown that, under influence of the quantum backreaction, the horizon of such a kind moves to a new position, near which the metric does not change its asymptotics, so the ultraextremal black holes and cosmological spacetimes do exist as self-consistent solutions of the semiclassical field equations.References addedGeneral Relativity and Quantum CosmologyHigh Energy Physics - Theorytext