Description
Neutron beta decay experiments provide weak interaction parameters, the nucleon axial form factor $g_\mathrm{A}$ and the element of the Cabibbo-Kobayashi-Maskawa matrix element $V_\mathrm{ud}$. In the framework of effective field theories, they serve to restrict couplings beyond the left-handed vector and axial-vector couplings of the Standard Model. The number of observables largely exceeds the number of parameters describing neutron $\beta$-decay which consequently enables sensitive searches for new physics and allows to check for consistency. Of particular interest is the Fierz interference term that provides sensitivity to scalar and tensor couplings. Transverse electron-polarization related decay correlation coefficients provide an additional probe of new physics. The aim of current and future experiments is to determine the Standard Model parameters and to place limits on hypothetical effective interactions with unprecedented precision.