The oblique parameters from arbitrary new fermions

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 $SU(2)\times U(1)$, 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 $SU(2)\times U(1)$ that they sit in. We apply our general computation to two illustrative cases.