The oblique parameters from arbitrary new fermions

Abstract

We compute the six oblique parameters S, T, U, V, W, X in a New Physics Model with an arbitrary number of new fermions, in arbitrary representations of SU(2) × U(1), and mixing arbitrarily among themselves. We show that S and U are automatically finite, but T is finite only if there is a specific relation between the masses of the new fermions and the representations of SU(2) × U(1) that they sit in. We apply our general computation to two illustrative cases.