2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/229814Measurements of neutron beta decay observables required to determine $|V_{ud}|$ are reaching the 0.1% accuracy. In this paper we review the calculation of the decay rate of this process, discuss its relevant uncertainties, and obtain an expression that is precise at the $10^{-4}$ level. Our analysis clearly shows the necessity of measurements of $λ$, the ratio of axial/vector couplings. The current situation in neutron beta decay is that one cannot yet quote a single consistent value for $|V_{ud}|$ from it. We also discuss the region of parameter space in the $|V_{ud}|$--$λ$ plane where new physics effects should lie, if they contribute to neutron beta decay.14 latex pages, 1 eps figure, submitted to Physics Letter BNuclear TheoryHigh Energy Physics - PhenomenologyNuclear Experimenttext