Ben Craps

What is special Kahler geometry

The scalars in vector multiplets of N = 2 supersymmetric theories in four dimensions exhibit ‘special Kahler geometry’, related to duality symmetries, due to their coupling to the vectors. In the literature there is some confusion on the definition of special geometry. We show equivalences of some definitions and give examples which show that earlier definitions are not equivalent, and are not sufficient to restrict the Kahler metric to one that occurs in N = 2 supersymmetry. We treat the rigid as well as the local supersymmetry case. The connection is made to moduli spaces of Riemann surfaces and Calabi-Yau 3-folds. The conditions for the existence of a prepotential translate to a condition on the choice of canonical basis of cycles.

Anomalous D-brane and orientifold couplings from the boundary state

Abstract We compute scattering amplitudes involving both R-R and NS-NS fields in the presence of a D-brane or orientifold plane. These provide direct evidence for the anomalous couplings in the D-brane and orientifold actions. The D9-brane and O9-plane are found to couple to the first Pontrjagin class with the expected relative strength.

BPS solutions of a D5-brane worldvolume in a D3-brane background from superalgebras

The BPS method is used to find BPS solutions of the worldvolume theory of a D5-brane in the near horizon geometry of a D3-brane. The BPS bound is interpreted in terms of the `maximally extended D5 worldvolume supersymmetry algebra in the corresponding curved background, which is OSp(1|16). This algebra is an extension of the worldvolume superalgebra OSp(4*|4). The analysis is generalized to the non-near horizon case.

Ramond-Ramond couplings of non-BPS D-branes

We study how non-BPS type II D-branes couple to R-R potentials. Upon tachyon condensation the couplings we find give rise to the Wess-Zumino action of BPS D-branes.

D-branes in type 0 string theory

Abstract Using boundary states we derive the presence of (chiral) fermions on the intersection of type 0 D-branes. The corresponding anomalous couplings on the branes are then computed. Furthermore, we discuss systems of branes at C 2 / Z n orbifold singularities. In particular, the massless spectrum on the branes is derived, and a boundary state description is given.

(NON-)ANOMALOUS D-BRANE AND O-PLANE COUPLINGS : THE NORMAL BUNDLE

Abstract The direct string computation of anomalous D-brane and orientifold plane couplings is extended to include the curvature of the normal bundle. The normalization of these terms is fixed unambiguously. New, non-anomalous gravitational couplings are found.

NS fivebranes in type 0 string theory

The massless degrees of freedom of type 0 NS5-branes are derived. A non-chiral, purely bosonic spectrum is found in both type 0A and 0B. This non-chirality is confirmed by a one-loop computation in the bulk. Some puzzles concerning type 0B S-duality are pointed out in this context. An interpretation of the spectra in terms of ``type 0 little strings is proposed.

Special Kahler geometry

Special (Kahler) geometry [2] is, by definition, the geometry of vectormultiplet scalars in N = 2 supergravity. However, one would like to define this geometry only referring to these scalars, not to any other fields. Therefore one needs to know the most general way of coupling vectormultiplets to supergravity. Originally, supergravity actions for vectormultiplets were constructed using a holomorphic ‘prepotential’. As turned out later, duality transformations can lead to actions for which a prepotential does not exist [4]. In [1] a formulation (‘definition’) of special geometry was given which is manifestly invariant under duality transformations. It was proved that this formulation is equivalent to the original one, in the sense that it is always possible to perform a duality transformation such that a prepotential exists in the dual formulation of the theory. Moreover, it describes all presently known examples of special geometry. All constraints imposed in this definition have a nice physical interpretation (related to duality invariance and positivity of the kinetic energy), except for one constraint in the special case of only one vectormultiplet. This exception suggests that one could try to construct a more general supergravity theory for one vectormultiplet, one that could not be encoded in a holomorphic prepotential.

Anomalous Couplings Of Non-BPS D-Branes

Non-BPS type II D-branes couple to R-R potentials via an action that, upon tachyon condensation, gives rise to the Wess-Zumino action of BPS D-branes.