Person:

Denef, Frederik

The limiting procedure of special Kähler manifolds to their rigid limit is studied for moduli spaces of Calabi-Yau manifolds in the neighbourhood of certain singularities. In two examples we consider all the periods in and around the rigid limit, identifying the non-trivial ones in the limit as periods of a meromorphic form on the relevant Riemann surfaces. We show how the Kähler potential of the special Kähler manifold reduces to that of a rigid special Kähler manifold. We make extensive use of the structure of these Calabi-Yau manifolds as K3 fibrations, which is useful to obtain the periods even before the K3 degenerates to an ALE manifold in the limit. We study various methods to calculate the periods and their properties. The development of these methods is an important step to obtaining exact results from supergravity on Calabi-Yau manifolds.

We study the attractor mechanism in low energy effective D=4, N=2 Yang-Mills theory weakly coupled to gravity, obtained from the effective action of type IIB string theory compactified on a Calabi-Yau manifold. Using special Kahler geometry, the general form of the leading gravitational correction is derived, and from this the attractor equations in the weak gravity limit. The effective Newton constant turns out to be spacetime-dependent due to QFT loop and nonperturbative effects. We discuss some properties of the attractor solutions, which are gravitationally corrected dyons, and their relation with the BPS spectrum of quantum Yang-Mills theory. Along the way, we obtain a satisfying description of Strominger's massless black holes, moving at the speed of light, free of pathologies encountered in some earlier proposals.

We begin by presenting the superparticle action in the background of N=2, D=4 supergravity coupled to n vector multiplets interacting via an arbitrary special Kahler geometry. Our construction is based on implementing kappa-supersymmetry. In particular, our result can be interpreted as the source term for N=2 BPS black holes with a finite horizon area. When the vector multiplets can be associated to the complex structure moduli of a Calabi-Yau manifold, then our 0-brane action can be derived by wrapping 3-branes around 3-cycles of the 3-fold. Our result can be extended to the case of higher supersymmetry; we explicitly construct the kappa supersymmetric action for a superparticle moving in an arbitrary N=8 supergravity background with 1/2, 1/4 or 1/8 residual supersymmetry.

We discuss, in the framework of special Kahler geometry, some aspects of the "rigid limit" of type IIB string theory compactified on a Calabi-Yau threefold. We outline the general idea and demonstrate by direct analysis of a specific example how this limit is obtained. The decoupling of gravity and the reduction of special Kahler geometry from local to rigid is demonstrated explicitly, without first going to a noncompact approximation of the Calabi-Yau. In doing so, we obtain the Seiberg-Witten Riemann surfaces corresponding to different rigid limits as degenerating branches of a higher genus Riemann surface, defined for all values of the moduli. Apart from giving a nice geometrical picture, this allows one to calculate easily some gravitational corrections to e.g. the Seiberg-Witten central charge formula. We make some connections to the 2/5-brane picture, also away from the rigid limit, though only at the formal level.