A general study of decaying scalar dark matter: existing limits and projected radio signals at the SKA

Abstract

We consider a decaying scalar dark matter (DM) with mass m χ in the range 10 GeV -10 TeV and vary the branching ratios of all possible two-body SM final states (excluding and including ν ν) in the range 0% − 100% to derive constraints on the total decay width Γ by combining the data collected by several astrophysical and cosmological observations. We find that, Γ 10 −26 − 10 −27 s −1 (excluding ν ν) and Γ 10 −24 − 10 −26 s −1 (including ν ν) are allowed, depending on the values of m χ , which are most robust upper limits on Γ for a generic decaying scalar DM. We then investigate the prospect of the upcoming Square Kilometer Array (SKA) radio telescope in detecting the DM decay induced radio signals originating inside the dwarf spheroidal (dSph) galaxies. We have classified the DM parameter space, allowed by the existing observations, independently of the branching ratio in each individual two-body SM final state, based on the detectability at the SKA. Excluding the ν ν decay mode, we find that, throughout the DM mass range 10 GeV -10 TeV, Γ > ∼ 10 −30 s −1 − 10 −29 s −1 is detectable for all possible branching ratio combinations at the SKA (for 100 hours of observation time), with conservative choices for the relevant astrophysical parameters. On the other hand, when arbitrary branching ratios are allowed also for the ν ν decay mode, DM decays can be probed model-independently for Γ > ∼ 2 × 10 −29 s −1 provided DM masses are greater than a few hundreds of GeV.

Dark Matter decay to neutrinos

“…What's more the observation of an electromagnetic counterpart will be key in the event of a discovery. Intriguingly, the Square Kilometre Array (SKA) will be sensitive to χ → νν [29] in nearby dwarf galaxies for DM masses above a few hundred GeV. Taken together, these observations highlight the importance of multimessenger observations when it comes to elucidating the nature of dark matter.…”

“…In many of these models, UV physics can destabilize the DM, leading to a decay to νν, which may dominate over other channels. These models have motivated numerous dedicated studies, mainly in the context of discovering heavy DM using neutrino line searches [24][25][26][27][28][29], and many neutrino experiments have hunted for DM signatures in their observations [30][31][32][33][34][35], so far yielding null results.…”