Opening up New Parameter Space for Sterile Neutrino Dark Matter

Abstract

Sterile neutrinos are compelling dark matter (DM) candidates, yet the minimal production mechanism solely based on active ($ν_a$)-sterile ($ν_s$) oscillations is excluded by astrophysical observations. Non-standard self-interactions in either active ($ν_a-ν_a$) or sterile ($ν_s-ν_s$) sector are known to alter the sterile neutrino DM production in the early Universe, which could alleviate the tension with astrophysical constraints to some extent. Here we propose a novel solution where scalar-mediated non-standard interactions between active and sterile neutrinos ($ν_a-ν_s$) generate new production channels for $ν_s$, independent of the active-sterile mixing and without the need for any fine-tuned resonance or primordial lepton asymmetry. This framework enables efficient sterile neutrino DM production even at vanishingly small mixing angles and opens up new viable regions of parameter space that can be tested with future $X$-ray and gamma-ray observations.

Figures (11)

• Figure 1: Sterile neutrino mass versus mixing angle for a fixed active-sterile neutrino coupling $y_{as}=3 \times 10^{-4}$. Shaded regions indicate astrophysical constraints, while the open curves on the left represent future $X$-ray sensitivities. Red dotted and dashed curves show projected $\beta$-decay experiment sensitivities. The gray dashed line marks the sterile neutrino lifetime equal to the age of the Universe. The blue contours satisfy the correct DM relic abundance $\Omega_s h^2 = 0.12$ for different values of the mediator mass $m_\phi$. The black line corresponds to the correct relic density using the DW mechanism. The red star marks a benchmark point (BP) used later to illustrate the yield behavior. The blue point corresponds to the purported 3.5 keV $X$-ray line signal.
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