2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/199712We review our recent work on the existence of a new independent R^4 term, at one loop, in the type IIA and heterotic effective actions, after reduction to four dimensions, besides the usual square of the Bel-Robinson tensor. We discuss its supersymmetrization.1+7 pages. Work presented at the XVI International Fall Workshop on Geometry and Physics, Lisbon, Portugal, September 2007High Energy Physics - Theorytext