Boris Pioline, Université Paris 6 and CERN
Title: BPS amplitudes, theta lifts and the Kawazumi-Zhang invariant
Abstract: Protected couplings in the low energy effective action of toroidal compactifications are typically expressed as regularized theta lifts, i.e. modular integrals of a Siegel-Narain theta series times a real-analytic Siegel modular form. In this talk I will focus on $\cR^4$, $D^4\cR^4$, $D^6 \cR^4$ couplings in type II strings compactified on a torus. By analyzing the constraints from supersymmetry and duality, I will motivate and establish a new theta lift representation for the Kawazumi-Zhang invariant, which enters in the integrand of the two-loop $D^6 \cR^4$ coupling.