  The functional renormalization group has become a widely used tool for the
analysis of the leading low-temperature correlations in weakly to moderately
coupled many-fermion lattice systems. A bottleneck for quantitatively more
precise results is that the treatment of the frequency dependence of the
flowing interactions is numerically quite demanding. Yet the frequency
dependence is needed to compute relevant selfenergies and hence for controlled
results on the energy scales for ordering or for the quasiparticle properties.
Here we explore an approximate parametrization of the frequency dependence of
the interaction vertex that is inspired by established simplifications in the
theory of superconductivity and that keeps the numerical effort bounded. We
demonstrate the validity of the approximation for Cooper pairing problems and
apply it to the two-dimensional Hubbard model.
