  We propose a novel parametrization of the four-point vertex function in the
one-loop one-particle irreducible renormalization group (RG) scheme for
fermions. It is based on a decomposition of the effective two-fermion
interaction into fermion bilinears that interact via exchange bosons. Besides
being more efficient than previous N-patch schemes, this parametrization also
reduces the ambiguity of introducing boson fields. We apply this
parametrization to the two-dimensional (t,t')-Hubbard model using a novel
$\Omega$-frequency regularization.
