SIMP dark matter and its cosmic abundances

Soo-Min Choi,Min-Seok Seo,Hyun Min Lee,B Gwak,S Lee,H.-C Kim,W Lee,J Lee,C.-H Lee,G Kang,C Kim

doi:10.1051/epjconf/201816806009

Abstract

We give a review on the thermal average of the annihilation cross-sections for 3 → 2 and general higher-order processes. Thermal average of higher order annihilations highly depend on the velocity of dark matter, especially, for the case with resonance poles. We show such examples for scalar dark matter in gauged Z3 models.

Highlights

Dark matter has been hinted by missing masses in galaxies and galaxy clusters and supported by indirect evidences such as Cosmic Microwave Background(CMB) or gravitational lensing effect
For the non-relativistic dark matter, if the cross-section has a resonance of Breit-Wigner form and the sum of masses for initial particles are almost the same as the resonance mass, the thermal averaged cross-section is very sensitive to the velocities of initial dark matter particles
Because the phase space integral in the thermal average for SIMP depends on the higher order of dark matter velocity than in the case of WIMP, SIMP case highly depends on the resonance mass ( R2) than WIMP case ( R1/2)

Summary

Introduction

Dark matter has been hinted by missing masses in galaxies and galaxy clusters and supported by indirect evidences such as Cosmic Microwave Background(CMB) or gravitational lensing effect. The most popular candidate for dark matter is Weakly Interacting Massive Particle(WIMP), and WIMP has 2 → 2 annihilation channels into the Standard Model particles. WIMP relic density is determined when the 2 → 2 annihilation channels are frozen out. The popular candidate for self-interacting dark matter is Strongly Interacting Massive Particle(SIMP) [1]. SIMP has a 3 → 2 self-annihilation process between dark matter particles determining the current relic density when it is frozen-out. Expanded as powers of dark matter relative velocity and the lowest order terms of relative velocity are the most important. This applies to high order annihilations such as SIMP, especially when there is a higher partial wave or resonance pole. We discuss the thermal averaged cross-section of high order annihilations for SIMP and perform a valid thermal average of the velocity dependent cross-section such as in the case with resonance pole

Resonance and thermal average

Thermal average of SIMP

Model for resonant SIMP

Conclusions