Earthly probes of the smallest dark matter halos

TL;DR

This paper investigates how the smallest dark matter structures relate to detection signals, focusing on neutralino and Kaluza-Klein dark matter models, and finds strong correlations especially for spin-dependent interactions and neutrino fluxes.

Contribution

It demonstrates the correlation between dark matter detection signals and the size of the smallest dark matter halos in specific particle models, providing analytic insights.

Findings

Strong correlation between spin-dependent cross section and kinetic decoupling temperature.

Tight correlation between neutrino flux from the Sun and dark matter properties.

Poor correlation between scalar neutralino-nucleon cross section and decoupling temperature.

Abstract

Dark matter kinetic decoupling involves elastic scattering of dark matter off of leptons and quarks in the early universe, the same process relevant for direct detection and for the capture rate of dark matter in celestial bodies; the resulting size of the smallest dark matter collapsed structures should thus correlate with quantities connected with direct detection rates and with the flux of high-energy neutrinos from dark matter annihilation in the Sun or in the Earth. In this paper we address this general question in the context of two widely studied and paradigmatic weakly-interacting particle dark matter models: the lightest neutralino of the minimal supersymmetric extension of the Standard Model, and the lightest Kaluza-Klein particle of Universal Extra Dimensions (UED). We argue and show that while the scalar neutralino-nucleon cross section correlates poorly with the kinetic decoupling temperature, the spin-dependent cross section exhibits a strong correlation in a wide range of models. In UED models the correlation is present for both cross sections, and is extraordinarily tight for the spin-dependent case. A strong correlation is also found, for both models, for the flux of neutrinos from the Sun, especially for fluxes large enough to be at potentially detectable levels. We provide analytic guidance and formulae that illustrate our findings.