On the geometric approach to the boundary problem in supergravity

TL;DR

This paper reviews the geometric superspace approach to boundary problems in supergravity, focusing on boundary contributions, supersymmetry invariance, and applications to holography in four-dimensional theories with different cosmological constants.

Contribution

It provides a comprehensive geometric framework for supergravity boundary problems, including boundary terms, supersymmetry invariance, and reformulation in MacDowell-Mansouri form, with applications to holography.

Findings

Boundary terms are necessary for supersymmetry invariance.

Superfield strengths are fixed at the boundary to constant values.

The Lagrangian can be expressed in a MacDowell-Mansouri-like form.

Abstract

We review the geometric superspace approach to the boundary problem in supergravity, retracing the geometric construction of four-dimensional supergravity Lagrangians in the presence of a non-trivial boundary of spacetime. We first focus on pure $\mathcal{N}=1$ and $\mathcal{N}=2$ theories with negative cosmological constant. Here, the supersymmetry invariance of the action requires the addition of topological (boundary) contributions which generalize at the supersymmetric level the Euler-Gauss-Bonnet term. Moreover, one finds that the boundary values of the super field-strengths are dynamically fixed to constant values, corresponding to the vanishing of the $\mathrm{OSp}(\mathcal{N}|4)$-covariant supercurvatures at the boundary. We then consider the case of vanishing cosmological constant where, in the presence of a non-trivial boundary, the inclusion of boundary terms involving additional fields, which behave as auxiliary fields for the bulk theory, allows to restore supersymmetry. In all the cases listed above, the full, supersymmetric Lagrangian can be recast in a MacDowell-Mansouri(-like) form. We then report on the application of the results to specific problems regarding cases where the boundary is located asymptotically, relevant for a holographic analysis.