Computation of RR tadpoles
The simplest way to evaluate the total tadpoles is to compute the sum of Klein bottle, Moebius strip, and cylinder diagrams, transform them into the dual channel, and factorize them. As shown in Figure D.1, the result is the square of the disk plus crosscap tadpole (or sums thereof for various fields). In supersymmetric models, the total amplitude vanishes due to a cancellation of NSNS and RR closed string exchanges. Yet the consistency of the models requires the cancellation of the tadpoles for the diverse RR fields, which are extracted from the RR exchange piece in this factorization limit.