Superstring Perturbation Theory
In this talk I will show how to use the pure spinor formalism to compute multiloop string amplitudes, including their precise overall coefficients. I will also discuss the relevance of the recent four-point 3-loop and five-point 2-loop amplitudes for verifying some S-duality predictions.
We present a string-inspired method to construct supersymmetric loop integrands for scattering amplitudes in ten-dimensional SYM and supergravity. The kinematic dependence is described in pure spinor superspace and determined from the BRST-symmetry of the underlying pure spinor superstring. We focus on five-point examples at one- and two-loop order which satisfy the BCJ duality between color and kinematics. Hence, the supergravity integrands follow straightforwardly from a double copy construction of the cubic diagrams in SYM.
After reviewing its structure and discussing the twistor-like origin of the pure spinor formalism, I will speculate on possible applications for AdS_5xS^5 and M-theory
The operator formalism provides a constructive approach to superstring amplitudes that has two main virtues: it makes it possible to study explicitly all the degeneration limits and it is flexible enough to work in different setups. I will illustrate these two features in a concrete example: the twisted open string partition function at two loops, which describes the interactions between three D-branes in type II theories.
The conventional on-shell techniques of computing string theory amplitudes is not sufficient to compute mass renormalization of massive states and vacuum shift in string theory. The aim of this talk is to define a suitable off-shell continuation of Polyakov approach. Then this off-shell continuation will be used to compute mass-renormalization and perturbative vacuum shift in string theory.