We calculate the effects of including dynamical fermion loops in the lattice QCD estimates of meson decay constants, by extrapolating the results from negative flavour numbers after a suitable matching of the pion and rho mass. For moderately light quarks, the values of the decay constants not corrected for the renormalization constants increase with respect to their quenched values.
@article{arxiv.hep-lat/9510048,
title = {Light meson decay constants beyond the quenched approximation},
author = {G. M. de Divitiis and R. Frezzotti and M. Guagnelli and M. Masetti and R. Petronzio},
journal= {arXiv preprint arXiv:hep-lat/9510048},
year = {2009}
}