Self-heating of strongly interacting massive particles

Hyungjin Kim,Ayuki Kamada,Hee Jung Kim

doi:10.1103/physrevd.98.023509

Abstract

It was recently pointed out that semi-annihilating dark matter (DM) may experience a novel temperature evolution dubbed as self-heating. Exothermic semi-annihilation converts the DM mass to the kinetic energy. This yields a unique DM temperature evolution, $T_{\chi} \propto 1 / a$, in contrast to $ T_{\chi} \propto 1 / a^{2}$ for free-streaming non-relativistic particles. Self-heating continues as long as self-scattering sufficiently redistributes the energy of DM particles. In this paper, we study the evolution of cosmological perturbations in self-heating DM. We find that sub-GeV self-heating DM leaves a cutoff on the subgalactic scale of the matter power spectrum when the self-scattering cross section is $\sigma_{\rm self} / m_{\chi} \sim {\cal O} (1) \,{\rm cm}^{2} /{\rm g}$. Then we present a particle physics realization of the self-heating DM scenario. The model is based on recently proposed strongly interacting massive particles with pion-like particles in a QCD-like sector. Pion-like particles semi-annihilate into an axion-like particle, which is thermalized with dark radiation. The dark radiation temperature is smaller than the standard model temperature, evading the constraint from the effective number of neutrino degrees of freedom. It is easily realized when the dark sector is populated from the standard model sector through a small coupling.

Highlights

Accumulated observational data begin to test our understanding of how dark matter (DM) is distributed over the Universe and how the DM distribution evolves in time [1]
Self-heating of semiannihilating DM can suppress subgalactic-scale structure formation when it lasts until the matter-radiation equality
The reduced number of dwarf-size halos can reconcile the possible tension between the cold dark matter (CDM) paradigm and the observation

Summary

INTRODUCTION

Accumulated observational data begin to test our understanding of how dark matter (DM) is distributed over the Universe and how the DM distribution evolves in time [1]. Gravitational clustering of WDM particles is interrupted on a subgalactic scale because of a sizable thermal velocity of v=c ∼ 10−3 − 10−4 at the matter-radiation equality. This suppresses dwarf-size halo formation [10,11]. A sterile neutrino with a keV mass is a good benchmark model of WDM, where its phenomenology is described by the mass and the mixing angle with an active neutrino in the simplest setup [12] Another example is the core-cusp problem: Some dwarfsize halos have a cuspy profile as predicted by CDM, while others have a cored profile [13,14,15]. We investigate the impact of DM selfheating on the matter distribution of the Universe and propose a viable particle physics realization of self-heating DM. In Appendix B, we present the evolution equations of cosmological perturbations in the selfheating DM scenario

THERMAL HISTORY OF SELF-HEATING DM FROM THE FREEZE-OUT TO STRUCTURE FORMATION

Homogeneous and isotropic evolution

Perturbed evolution

EXTENDED SIMP MODEL WITH AN ALP AND DARK RADIATION

CONCLUSION

E E ðB7Þ θ0χ