N=31, D=11

TL;DR

The paper proves that eleven-dimensional supergravity backgrounds with 31 supersymmetries are actually maximally supersymmetric, and N=15 solutions in type I supergravity are Minkowski, ruling out certain preonic solutions.

Contribution

It demonstrates that N=31 supergravity backgrounds are equivalent to maximally supersymmetric ones, and N=15 solutions are Minkowski, clarifying the structure of supersymmetric solutions.

Findings

N=31 backgrounds admit an extra Killing spinor

N=15 solutions are locally Minkowski

Preonic solutions do not exist in eleven-dimensional supergravity

Abstract

We show that eleven-dimensional supergravity backgrounds with thirty one supersymmetries, N=31, admit an additional Killing spinor and so they are locally isometric to maximally supersymmetric ones. This rules out the existence of simply connected eleven-dimensional supergravity preons. We also show that N=15 solutions of type I supergravities are locally isometric to Minkowski spacetime.