Naturalness of MSSM dark matter

TL;DR

This paper rigorously analyzes the dark matter fine-tuning problem within the MSSM, considering various neutralino scenarios and mechanisms, and discusses how these impact naturalness and experimental signatures.

Contribution

It provides a comprehensive, model-independent assessment of dark matter fine-tuning in MSSM, integrating it with electroweak fine-tuning and exploring multiple neutralino configurations.

Findings

Favours the h-funnel scenario when neutralino mass is not near half the Higgs mass

Pure wino case is less favored due to fine-tuning considerations

Results are robust and applicable across different MSSM models

Abstract

There exists a vast literature examining the electroweak (EW) fine-tuning problem in supersymmetric scenarios, but little concerned with the dark matter (DM) one, which should be combined with the former. In this paper, we study this problem in an, as much as possible, exhaustive and rigorous way. We have considered the MSSM framework, assuming that the LSP is the lightest neutralino, $\chi_1^0$, and exploring the various possibilities for the mass and composition of $\chi_1^0$, as well as different mechanisms for annihilation of the DM particles in the early Universe (well-tempered neutralinos, funnels and co-annihilation scenarios). We also present a discussion about the statistical meaning of the fine-tuning and how it should be computed for the DM abundance, and combined with the EW fine-tuning. The results are very robust and model-independent and favour some scenarios (like the h-funnel when $M_{\chi_1^0}$ is not too close to $m_h/2$) with respect to others (such as the pure wino case). These features should be taken into account when one explores "natural SUSY" scenarios and their possible signatures at the LHC and in DM detection experiments.