D-Branes, Moduli and Supersymmetry

TL;DR

This paper investigates how antisymmetric tensor moduli influence D-brane supersymmetry conditions in Type II string theory compactified on tori, revealing new BPS configurations and implications for black hole state counting.

Contribution

It demonstrates the necessity of moduli-dependent modifications to supersymmetry projections and identifies new supersymmetric brane configurations at angles.

Findings

Moduli fields alter supersymmetry projections for D-branes.

Existence of supersymmetric branes at angles due to moduli effects.

Implications for counting black hole microstates in string theory.

Abstract

We study toroidal compactifications of Type II string theory with D-branes and nontrivial antisymmetric tensor moduli and show that turning on these fields modifies the supersymmetry projections imposed by D-branes. These modifications are seen to be necessary for the consistency of T-duality. We also show the existence of unusual BPS configurations of branes at angles that are supersymmetric because of conspiracies between moduli fields. Analysis of the problem from the point of view of the effective field theory of massless modes shows that the presence of a 2-form background must modify the realization of supersymmetry on the brane. In particular, the appropriate supersymmetry variation of the physical gaugino vanishes in any constant field strength background. These considerations are relevant for the $E_7$-symmetric counting of states of 4-dimensional black holes in Type II string theory compactified on $T^6$.