Killing superalgebras for Lorentzian six-manifolds

TL;DR

This paper computes the Spencer cohomology of six-dimensional (1,0) Poincaré superalgebras to identify geometries with maximal supersymmetry, revealing two branches of solutions including Lorentzian Lie groups and specific backgrounds distinguished by causal properties.

Contribution

It introduces a method to determine Killing spinor equations from Spencer cohomology and classifies maximally supersymmetric geometries in six dimensions.

Findings

Maximally supersymmetric backgrounds include Lorentzian Lie groups with bi-invariant metrics.

Identifies three distinct maximally supersymmetric backgrounds based on the causal type of a one-form.

Provides a classification of geometries admitting the maximal number of Killing spinors.

Abstract

We calculate the Spencer cohomology of the $(1,0)$ Poincar\'e superalgebras in six dimensions: with and without R-symmetry. As the cases of four and eleven dimensions taught us, we may read off from this calculation a Killing spinor equation which allows the determination of which geometries admit rigidly supersymmetric theories in this dimension. We prove that the resulting Killing spinors generate a Lie superalgebra and determine the geometries admitting the maximal number of such Killing spinors. They are divided in two branches. One branch consists of the lorentzian Lie groups with bi-invariant metrics and, as a special case, it includes the lorentzian Lie groups with a self-dual Cartan three-form which define the maximally supersymmetric backgrounds of $(1,0)$ Poincar\'e supergravity in six dimensions. The notion of Killing spinor on the other branch does not depend on the choice of a three-form but rather on a one-form valued in the R-symmetry algebra. In this case, we obtain three different (up to local isometry) maximally supersymmetric backgrounds, which are distinguished by the causal type of the one-form.