Natural NMSSM after LHC Run I and the Higgsino dominated dark matter scenario

TL;DR

This paper examines the naturalness of the NMSSM after LHC Run I, proposing a Higgsino-dominated dark matter scenario with low fine-tuning that can be tested at future colliders and detection experiments.

Contribution

It identifies a natural NMSSM scenario with minimal fine-tuning and Higgsino-dominated dark matter, consistent with LHC constraints and capable of being tested in future experiments.

Findings

LHC Run I constraints do not significantly worsen NMSSM fine-tuning.

A Higgsino-dominated neutralino DM scenario with low fine-tuning is viable.

The scenario can be tested via 3 lepton plus missing energy signals or direct detection.

Abstract

We investigate the impact of the direct searches for SUSY at LHC Run I on the naturalness of the Next-to-Minimal Supersymmetric Standard Model (NMSSM). For this end, we first scan the vast parameter space of the NMSSM to get the region where the fine tuning measures $\Delta_Z$ and $\Delta_h$ at the electroweak scale are less than about 50, then we implement by simulations the constraints of the direct searches on the parameter points in the region. Our results indicate that although the direct search experiments are effective in excluding the points, the parameter intervals for the region and also the minimum reaches of $\Delta_Z$ and $\Delta_h$ are scarcely changed by the constraints, which implies that the fine tuning of the NMSSM does not get worse after LHC Run I. Moreover, based on the results we propose a natural NMSSM scenario where the lightest neutralino $\tilde{\chi}_1^0$ as the dark matter (DM) candidate is Higgsino-dominated. In this scenario, $\Delta_Z$ and $\Delta_h$ may be as low as 2 without conflicting with any experimental constraints, and intriguingly $\tilde{\chi}_1^0$ can easily reach the measured DM relic density due to its significant Singlino component. We exhibit the features of the scenario which distinguish it from the other natural SUSY scenario, including the properties of its neutralino-chargino sector and scalar top quark sector. We emphasize that the scenario can be tested either through searching for $3 l + E_T^{miss}$ signal at 14 TeV LHC or through future DM direct detection experiments.