2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/81680Using effective field theory, we calculate the S-factor for the hep process in a totally parameter-free formulation. The transition operators are organized according to chiral counting, and their matrix elements are evaluated using the realistic nuclear wave functions obtained in the correlated-hyperspherical-harmonics method. Terms of up to next-to-next-to-next-to-leading order in heavy-baryon chiral perturbation theory are considered. Fixing the only parameter in the theory by fitting the tritium β-decay rate, we predict the hep S-factor with accuracy better than \sim 20 %.4 pages, Revtex. Minor revision has been madeNuclear TheoryAstrophysicsHigh Energy Physics - Phenomenologytext