  We discuss the effective field theory (EFT) for nuclear beta decay. The
general quark-level EFT describing charged-current interactions between quarks
and leptons is matched to the nucleon-level non-relativistic EFT at the O(MeV)
momentum scale characteristic for beta transitions. The matching takes into
account, for the first time, the effect of all possible
beyond-the-Standard-Model interactions at the subleading order in the recoil
momentum. We calculate the impact of all the Wilson coefficients of the leading
and subleading EFT Lagrangian on the differential decay width in allowed beta
transitions. As an example application, we show how the existing experimental
data constrain the subleading Wilson coefficients corresponding to
pseudoscalar, weak magnetism, and induced tensor interactions. The data display
a 3.5 sigma evidence for nucleon weak magnetism, in agreement with the theory
prediction based on isospin symmetry.
