A new maximally supersymmetric background of IIB superstring theory

TL;DR

This work identifies and constructs a new maximally supersymmetric background of IIB supergravity, realized as a Cahen–Wallach lorentzian symmetric space with a null homogeneous self-dual F5 flux. It provides the explicit metric and flux, proves the existence of 32 Killing spinors, and derives the full symmetry superalgebra, showing a non-semisimple 30-dimensional bosonic isometry group acting with 32 supercharges. The paper then explores how this background behaves under T-duality, compactification, and uplift to M-theory, uncovering radii-related supersymmetry enhancements, and illustrating the interplay between IIB and M-theory descriptions via stringy and winding-mode symmetries. Together with the KSKG-like KG predecessor in M-theory, this background broadens the catalog of exact RR backgrounds with maximal supersymmetry and provides a tractable setting for future string-theoretic analyses.

Abstract

We present a maximally supersymmetric IIB string background. The geometry is that of a conformally flat lorentzian symmetric space G/K with solvable G, with a homogeneous five-form flux. We give the explicit supergravity solution, compute the isometries, the 32 Killing spinors, and the symmetry superalgebra, and then discuss T-duality and the relation to M-theory.