[Paper Review] Prospects for Sneutrino Dark Matter in the BLSSM

Luigi Delle Rose, Shaaban Khalil+5 more|arXiv (Cornell University)|Apr 25, 2018

Dark Matter and Cosmic Phenomena3 citations

TL;DR

This paper investigates the right-handed sneutrino as a viable dark matter candidate in the B-L Supersymmetric Standard Model (BLSSM), showing it provides a natural and well-constrained alternative to the MSSM. It demonstrates that the BLSSM offers a significantly larger viable parameter space for dark matter while enabling indirect detection via gamma-ray signals, particularly from CP-odd and CP-even sneutrino decays, with potential observability in future high-energy gamma-ray telescopes.

ABSTRACT

The $(B-L)$ Supersymmetric Standard Model (BLSSM) motivates several Dark Matter (DM) candidates beyond the Minimally Supersymmetric Standard Model (MSSM). We assess the comparative naturalness of the two models and discuss the potential detection properties of a particular candidate, the Right-Handed (RH) sneutrino.

Motivation & Objective

• To assess the naturalness of the BLSSM compared to the MSSM under universal soft-breaking parameters.
• To evaluate the viability of the right-handed sneutrino as a dark matter candidate in the BLSSM framework.
• To analyze the direct, indirect, and collider detection prospects for sneutrino dark matter.
• To identify distinctive LHC signatures that could confirm sneutrino dark matter if observed.
• To determine whether CP-even and CP-odd sneutrino states can be disentangled via gamma-ray spectral features.

Proposed method

• Employed the fine-tuning (Δ) metric based on sensitivity of the Z-boson mass to variations in GUT-scale soft-breaking parameters (m₀, m₁/₂, A₀, μ, Bμ) and additional BLSSM parameters (μ′, Bμ′).
• Conducted a scan over parameter space using SPheno with constraints from HiggsBounds and HiggsSignals to ensure compatibility with LHC Higgs data.
• Fixed the Z′ gauge boson mass at 4 TeV to satisfy existing dilepton search limits from the LHC.
• Used MadGraph to simulate LHC production cross sections for sneutrino dark matter via mono-jet, Z′ decay, slepton, and squark pair production.
• Computed relic density and gamma-ray spectra from sneutrino annihilation, focusing on CP-even and CP-odd cases.
• Analyzed the spectral shape of final-state photons to assess distinguishability from neutralino signals and potential for future detection at higher energies.

Experimental results

Research questions

• RQ1 How does the naturalness of the BLSSM compare to the MSSM under the constrained MSSM (CMSSM) scenario?
• RQ2 What is the contribution of the right-handed sneutrino to the dark matter relic density in the BLSSM?
• RQ3 Can the CP-even and CP-odd sneutrino states be distinguished via indirect detection through their gamma-ray spectra?
• RQ4 What are the dominant LHC signatures for sneutrino dark matter production and decay, and are they observable with current or near-future experiments?
• RQ5 Can the BLSSM provide a viable dark matter candidate with a larger viable parameter space than the MSSM while satisfying all current experimental constraints?

Key findings

• The BLSSM exhibits comparable fine-tuning levels to the MSSM, with Δ < 500 in large regions of parameter space, indicating similar naturalness properties.
• The right-handed sneutrino provides a significantly larger viable parameter space for dark matter than the MSSM, due to its unique role in the Type-I see-saw mechanism.
• Indirect detection via gamma-ray emission is promising: the sneutrino can produce photons up to 661 GeV, exceeding the current experimental upper limit of ~300 GeV, suggesting potential observability in future high-energy telescopes.
• The gamma-ray spectra from CP-even and CP-odd sneutrino decays are indistinguishable from each other but differ characteristically from neutralino spectra, likely due to spin differences (scalar vs. fermion).
• LHC signatures such as mono-jet, Z′ → sneutrino pair production, slepton pair production, and squark decays offer distinct final states (e.g., multi-jet + multi-lepton), though cross sections are small (e.g., σ ≈ 0.025 fb for Z′ decay).
• Slepton and squark pair production offer larger cross sections (~0.1 fb), with decay chains involving heavy neutrinos providing fully or semi-leptonic final states that could be uniquely identified.