Higher derivative F-terms in N = 2 strings Original Research Article

We study a class of higher derivative F-terms of the form Fg,n W2g (Π f)n where W is the N = 2 gravitational superfield and Π is the chiral projector applied to a non-holomorphic function f of the heterotic dilaton vector superfield. We analyze these couplings in the heterotic theory on K3 × T2, where it is found they satisfy an anomaly equation which generalizes the previous found for Fg,0 terms in N = 2 type II vacua and some heterotic dual models. We recognize that, near a point of SU(2) enhancement, a given generating function of the leading singularity of the Fg,n reproduces the free energy of a c = 1 string at an arbitrary radius R. According to the N = 2 heterotic-type II duality in 4D, we then study these couplings near a conifold singularity, using its local description in terms of intersecting D-5-branes. In this context, it turns out that there exists, among the other states involved, a vector gauge field reproducing the heterotic leading singularity structure.