F-theory and orientifolds

Abstract

By analyzing F-theory on K3 near the orbifold limit of K3 we establish the equivalence between F-theory on K3 and an orientifold of type IIB on T^2, which in turn, is related by a T-duality transformation to type I theory on T^2. By analyzing the F-theory background away from the orbifold limit, we show that non-perturbative effects in the orientifold theory splits an orientifold plane into two planes, with non-trivial SL(2,Z) monodromy around each of them. The mathematical description of this phenomenon is identical to the Seiberg-Witten result for N=2 supersymmetric SU(2) gauge theory with four quark flavors. Points of enhanced gauge symmetry in the orientifold / F-theory are in one to one correspondence with the points of enhanced global symmetry in the Seiberg-Witten theory.