keV Warm Dark Matter via the Supersymmetric Higgs Portal

TL;DR

This paper proposes a supersymmetric model extending the MSSM to include a warm dark matter candidate, a gauge singlet fermion, with properties that naturally produce keV-scale masses suitable for resolving small-scale structure issues.

Contribution

The model uniquely links the fermion's mass to relic density and reheating temperature, ensuring the dark matter is necessarily warm and consistent with astrophysical observations.

Findings

Fermion mass range 0.3-4 keV for T_R between 10^2 and 10^5 GeV.

Reheating temperature T_R around 10-100 TeV yields primordial phase-space density matching dwarf galaxy observations.

Free-streaming length of 0.3-4 Mpc can address galaxy substructure problems.

Abstract

Warm dark matter (WDM) may resolve the possible conflict between observed galaxy halos and the halos produced in cold dark matter (CDM) simulations. Here we present an extension of MSSM to include WDM by adding a gauge singlet fermion, \bar{\chi}, with a portal-like coupling to the MSSM Higgs doublets. This model has the property that the dark matter is {\it necessarily warm}. In the case where M_{\bar{\chi}} is mainly due to electroweak symmetry breaking, the \bar{\chi} mass is completely determined by its relic density and the reheating temperature, T_R. For 10^2 GeV < T_{R} < 10^{5} GeV$, the range allowed by \bar{chi} production via thermal Higgs annihilation, the \bar{\chi} mass is in the range 0.3-4 keV, precisely the range required for WDM. The primordial phase-space density, Q, can directly account for that observed in dwarf spheroidal galaxies, Q \approx 5 x 10^{6}(eV/cm^3)/(km/s)^3,, when the reheating temperature is in the range T_R \approx 10-100 TeV, in which case M_{\bar{\chi}} \approx 0.45 keV. The free-streaming length is in the range 0.3-4 Mpc, which can be small enough to alleviate the problems of overproduction of galaxy substructure and low angular momentum of CDM simulations.