Dark matter in the Kim-Nilles mechanism

TL;DR

This paper explores the implications of the Kim-Nilles mechanism for dark matter, analyzing axino production, decay, and the resulting constraints on supersymmetric particles and their detection prospects.

Contribution

It provides a detailed analysis of axino-related dark matter scenarios within the Kim-Nilles mechanism, highlighting conditions for stability, decay, and relic abundance constraints.

Findings

Stable axinos must be very light or reheat temperatures low to avoid overclosure.

Decaying axinos can produce neutralinos that match observed dark matter density.

Light Higgsino-like particles with bino mixture are promising dark matter candidates with detectable cross-sections.

Abstract

The Kim-Nilles mechanism relates the $\mu$ term with the axion scale $f_a$, leading to the axino-Higgsino-Higgs Yukawa coupling of order $\mu/f_a$. This can bring a dangerous thermal production of axinos. If the axino is stable, its mass has to be as small as ${\cal O}$(0.1keV), or the reheat temperature should be lower than ${\cal O}$(10GeV) taking the lower axion scale $10^{10}$ GeV in order not to overclose the Universe. If the axino decays to a neutralino, the overproduced neutralinos can re-annihilate appropriately to saturate the observed dark matter density if the annihilation rate is of order $10^{-8}{GeV}^{-2}$ for the axion scale larger than about $10^{11}$ GeV. Thus, a light Higgsino-like lightest supersymmetric particle with a sizable bino mixture becomes a good dark matter candidate whose nucleonic cross-section is of order $10^{-45}$cm$^2$.