Green functions and twist correlators for $N$ branes at angles

Understand

We compute the Green functions and correlator functions for N twist fields for branes at angles on T^2 and we show that there are N-2 different configurations labeled by an integer M which is roughly associated with the number of obtuse angles of the configuration.

• In order to perform this computation we use a SL(2,R) invariant formulation and geometric constraints instead of Pochammer contours.
• In particular the M=1 or M=N-1 amplitude can be expressed without using transcendental functions.
• We determine the amplitudes normalization from N -> N-1 reduction without using the factorization into the untwisted sector.