Which weak-interaction theory did Feynman and Gell-Mann develop in 1958?

Feynman and Gell-Mann developed V−A theory, the vector-minus-axial-vector theory of weak interactions, in 1958.

The theory was designed to explain the unusual structure of weak decay after experiments established parity violation. Earlier descriptions based on Fermi’s theory treated beta decay as a four-fermion interaction, but the new evidence showed that the weak force could not respect mirror symmetry in the ordinary way.

V−A theory combines vector and axial-vector currents in a specific difference. This arrangement makes the weak interaction act on left-handed particles and right-handed antiparticles, providing a natural account of maximal parity violation. It became a major stepping stone toward the modern description of weak interactions.

A common mix-up is crediting the theory solely to Feynman and Gell-Mann without noting that Robert Marshak and George Sudarshan independently developed a closely related V−A formulation around the same period. Another confusion is with electroweak theory, later developed by Sheldon Glashow, Abdus Salam, and Steven Weinberg; V−A theory predates that unification.