Annihilations of superheavy dark matter in superdense clumps

TL;DR

This paper explores how superheavy dark matter, particularly neutralinos like binos and higgsinos, can form dense clumps that significantly enhance annihilation signals, potentially observable as ultrahigh energy particles.

Contribution

It demonstrates the formation of dense dark matter clumps from superheavy neutralinos and analyzes their impact on annihilation signals, considering different particle types and early universe conditions.

Findings

Dense clumps can form down to ~260 m_χ for binos.

Dense clumps may develop a gravithermal catastrophe, boosting annihilation.

Higgsinos' annihilation signals are enhanced by the Sommerfeld effect.

Abstract

Superheavy dark matter (SHDM) exchanges energy with its environment much slower than particles with masses close to the electroweak (EW) scale and has therefore different small-scale clustering properties. Using the neutralino as candidate for the SHDM, we find that free-streaming allows the formation of DM clumps of all masses down to $\sim 260 m_\chi$ in the case of bino. If small-scale clumps evolve from a non-standard, spiky spectrum of perturbations, DM clumps may form during the radiation dominated era. These clumps are not destroyed by tidal interactions and can be extremely dense. In the case of a bino, a "gravithermal catastrophe" can develop in the central part of the most dense clumps, increasing further the central density and thus the annihilation signal. In the case of a higgsino, the annihilation signal is enhanced by the Sommerfeld effect. As a result annihilations of superheavy neutralinos in dense clumps may lead to observable fluxes of annihilation products in the form of ultrahigh energy particles, for both cases, higgsinos and binos, as lightest supersymmetric particles.