Inverse mass expansion of the one-loop effective action

A method is described for the development of the one-loop effective action expansion as an asymptotic series in inverse powers of the fermion mass. The method is based on the Schwinger–DeWitt proper-time technique, which allows for loop particles with nondegenerate masses. The case with SU(2)×SU(2) as the symmetry group is considered. The obtained novel series generalizes the well-known Schwinger–DeWitt inverse mass expansion for equal masses, and is chiral invariant at each order. We calculate the asymptotic coefficients up to the fifth order and clarify their relationship with the standard Seeley–DeWitt coefficients.