2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/206876We have reexamined the electromagnetic corrections to the weak interaction rates for the transformation of neutrons to protons, and protons to neutrons, in the early universe, before freeze-out. We derive compact expressions for these rates in terms of thermal expectation values of products of fields, and we give explicit constructions of the terms to order e^2. We disagree in several respects with results in the literature.38 pages, 3 figures Two typos correctedAstrophysicsHigh Energy Physics - Phenomenologytext