“…In particular we discuss mode regularization for the N = 1, 2 nonlinear sigma models. These quantum mechanical models were originally used to calculate chiral [6,7,8] and trace anomalies [9,10] in a simpler way than using standard QFT Feynman rules 1 . They are also very useful to evaluate one-loop effective actions and scattering amplitudes for a Dirac (N = 1) or Maxwell/Proca field and differential forms (N = 2) coupled to scalar, antisymmetric tensor, gauge fields backgrounds [12,13,14,15,16], or to curved space-time (external gravity), as in [17,18,19,20] where i, k = 1, 2 are O(2) indices labeling fermion species; the term proportional to Rψψψψ is dictated by classical supersymmetry, while V contains the quantum counterterms.…”