Naturalness of Neutralino Dark Matter

TL;DR

This paper analyzes the fine-tuning of neutralino dark matter in the MSSM, considering recent experimental constraints, and identifies regions with low fine-tuning that remain viable under current and future searches.

Contribution

It provides a comprehensive assessment of neutralino dark matter fine-tuning in light of latest experimental bounds, highlighting surviving untuned solutions and their characteristics.

Findings

Current searches exclude large untuned parameter regions.

Resonant annihilation allows low fine-tuning at light masses.

Untuned solutions persist at higher masses, especially with negative .

Abstract

We investigate the level of fine-tuning of neutralino Dark Matter below 200 GeV in the low-energy phenomenological minimal supersymmetric Standard Model taking into account the newest results from XENON100 and the Large Hadron Collider as well as all other experimental bounds from collider physics and the cosmological abundance. We find that current and future direct Dark Matter searches significantly rule out a large area of the untuned parameter space, but solutions survive which do not increase the level of fine-tuning. As expected, the level of tuning tends to increase for lower cross-sections, but regions of resonant neutralino annihilation still allow for a band at light masses, where the fine-tuning stays small even below the current experimental limits for direct detection cross-sections. For positive values of the supersymmetric Higgs mass parameter \mu large portions of the allowed parameter space are excluded, but there still exist untuned solutions at higher neutralino masses which will essentially be ruled out if XENON1t does not observe a signal.For negative \mu untuned solutions are not much constrained by current limits of direct searches and, if the neutralino mass was found outside the resonance regions, a negative \mu-term would be favored from a fine-tuning perspective. Light stau annihilation plays an important role to fulfill the relic density condition in certain neutralino mass regions. Finally we discuss, in addition to the amount of tuning for certain regions in the neutralino mass-direct detection cross-section plane, the parameter mapping distribution if the allowed model parameter space is chosen to be scanned homogeneously (randomized).