Mass Bounds on a Very Light Neutralino

TL;DR

This paper investigates the mass bounds of the lightest neutralino within the MSSM, considering various experimental and observational constraints, and finds that a massless neutralino remains consistent with all current data.

Contribution

It provides a comprehensive analysis allowing for non-universal gaugino masses and demonstrates that a massless neutralino is still viable under current constraints.

Findings

Massless neutralino is compatible with collider data.

Laboratory and astrophysical constraints do not exclude a very light neutralino.

Neutralino mass bounds are broader than previously thought.

Abstract

Within the Minimal Supersymmetric Standard Model (MSSM) we systematically investigate the bounds on the mass of the lightest neutralino. We allow for non-universal gaugino masses and thus even consider massless neutralinos, while assuming in general that R-parity is conserved. Our main focus are laboratory constraints. We consider collider data, precision observables, and also rare meson decays to very light neutralinos. We then discuss the astrophysical and cosmological implications. We find that a massless neutralino is allowed by all existing experimental data and astrophysical and cosmological observations.