Bino Dark Matter and Big Bang Nucleosynthesis in the Constrained E6SSM with Massless Inert Singlinos

TL;DR

This paper explores a variant of the E6SSM with massless inert singlinos, proposing a new dark matter relic density mechanism and analyzing their impact on Big Bang Nucleosynthesis and effective neutrino species.

Contribution

It introduces a novel dark matter relic density mechanism involving inelastic scattering into inert Higgsinos and examines the cosmological implications of massless inert singlinos in the E6SSM.

Findings

Relic density achieved via inelastic bino scattering.

Massless inert singlinos contribute to Neff depending on Z' mass.

For Z' > 1300 GeV, Neff rac14; 3.2.

Abstract

We discuss a new variant of the E6 inspired supersymmetric standard model (E6SSM) in which the two inert singlinos are exactly massless and the dark matter candidate has a dominant bino component. A successful relic density is achieved via a novel mechanism in which the bino scatters inelastically into heavier inert Higgsinos during the time of thermal freeze-out. The two massless inert singlinos contribute to the effective number of neutrino species at the time of Big Bang Nucleosynthesis, where the precise contribution depends on the mass of the Z' which keeps them in equilibrium. For example for mZ' > 1300 GeV we find Neff \approx 3.2, where the smallness of the additional contribution is due to entropy dilution. We study a few benchmark points in the constrained E6SSM with massless inert singlinos to illustrate this new scenario.