From maximal to minimal supersymmetry in string loop amplitudes

Understand

We calculate one-loop string amplitudes of open and closed strings with N=1,2,4 supersymmetry in four and six dimensions, by compactification on Calabi-Yau and K3 orbifolds.

• In particular, we develop a method to combine contributions from all spin structures for an arbitrary number of legs at minimal supersymmetry.
• Each amplitude is cast into a compact form by reorganizing the kinematic building blocks and casting the worldsheet integrals in a basis.
• Infrared regularization plays an important role to exhibit the expected factorization limits.