one of the four known fundamental forces of nature and the one responsible for beta-decay radioactivity. The weak interaction is very short-ranged and more weakly coupled than either the strong nuclear force or electromagnetism. At energy scales above the Z mass the weak and electromagnetic interactions are unified (that is subject to a unified mathematical treatment).

Carrier bosons

The weak force is mediated by the exchange of three massive bosons: $W^{\pm}$ (mass about 80.4 GeV) and $Z^0$ (mass 91.2 GeV).

Conservation laws

Uniquely among the known forces the weak interaction violates flavor conservation in both the quark and lepton sectors, violates parity in purely leptonic interaction and violates charge-parity in some hadronic decay channels.