N=31 is not IIB

TL;DR

This paper proves that IIB supergravity backgrounds with 31 supersymmetries automatically have 32, ruling out the existence of preonic solutions and confirming all such backgrounds are maximally supersymmetric.

Contribution

It adapts the spinorial geometry method to demonstrate that near-maximal IIB supergravity backgrounds with 31 supersymmetries must be fully supersymmetric, showing no preonic solutions exist.

Findings

IIB backgrounds with 31 supersymmetries are actually maximally supersymmetric.

Preonic solutions in IIB supergravity do not exist.

The formalism confirms all near-maximal backgrounds are fully supersymmetric.

Abstract

We adapt the spinorial geometry method to investigate supergravity backgrounds with near maximal number of supersymmetries. We then apply the formalism to show that the IIB supergravity backgrounds with 31 supersymmetries preserve an additional supersymmetry and so they are maximally supersymmetric. This rules out the existence of IIB supergravity preons.