How light can the lightest neutralino be?

TL;DR

This paper demonstrates that within the MSSM, the lightest neutralino can be arbitrarily light if GUT relations are not assumed, affecting collider and precision measurements.

Contribution

It reveals that removing GUT constraints allows for an unconstrained lightest neutralino mass in the MSSM, challenging previous assumptions.

Findings

Neutralino mass can be arbitrarily low without GUT constraints.

Light or massless neutralinos impact LEP production and electroweak data.

Neutralino mass constraints depend on model assumptions.

Abstract

We show that in the Minimal Supersymmetric Standard Model, the mass of the lightest neutralino is experimentally unconstrained if the GUT relation between the gaugino mass parameters M_1 and M_2 is dropped. We discuss what the impact of light or massless neutralinos would be on their production at LEP, as well as on electroweak precision data and rare decays.