The Role of hidden ambiguities in the Linear Sigma Model with fermions
  The $U_L(3)\times U_R(3)$ Linear Sigma Model (LSM) with quark degrees of freedom is used to show that radiative corrections generate undetermined finite contributions. Their origin is related to surface terms which are differences between divergent integrals with the same degree of divergence. The technique used to detect these ambiguities is an implicit regularization on basic divergent integrals that do not depend on external momenta. We show that such contributions are absorbed by renormalization or fixed by symmetry requirements. The general expression for surface terms is derived. Renormalization group coefficients are calculated, as well as relevant observables for this model, such as $f_{\pi}$, $f_k$ and the pion and kaon form factors. 
Brigitte Hiller, A. L. Mota, M.C. Nemes, Alexander A. Osipov and   Marcos Sampaio