On the Gravitini Zero Modes riding on top of Multiple Black Holes

Abstract

We study gravitini zero modes in four dimensional $\mathcal{N} = 2$ pure supergravity theory. The gravitini zero modes we study are solutions to the Rarita-Schwinger equations of motion in the background of the purely bosonic Majumdar-Papapetrou background. We start with a very generic ansatz for the gravitini that involves $32$ ansatz functions and reduce the Rarita-Schwinger equations to a set of linear coupled partial differential equations on $\mathbf{R}^3$: the kind familiar from electromagnetism with divergences, curls etc. We first show how the gravitini zero modes due to broken supersymmetries arise in this set-up and how they solve the equations on $\mathbf{R}^3$. Then we go on and obtain other solutions to these equations: the `extra' fermion zero modes. If we count the fermion zero mode due to broken supersymmetries as one spinor worth of solutions, we have obtained three other spinors worth of solutions.