Abstract
We consider self-annihilation of dark matter, $\chi$, into metastable mediators, $Y$, and their subsequent decay into photons inside white dwarfs. We focus on reactions of the type $\chi \bar{\chi}\rightarrow YY$, where mediators, besides having a finite decay lifetime at rest $\tau_{\rm rest}\lesssim 1$ s, may suffer energy loss in the medium before they decay into photons, $Y \rightarrow \gamma\gamma$. We obtain attenuated gamma-ray luminosities arising from the combination of both effects. Using complementary sets of astrophysical measurements from cold white dwarfs in the M4 globular cluster as well as direct/indirect dark matter searches we discuss further constraints on dark mediator lifetimes.
Highlights
Dark matter (DM) accumulation sites can provide a valid strategy to potentially identify hints of DM proper existence as well as its nature and properties
Regarding DM itself, beyond standard model (BSM) candidates have flourished in the literature over the past decades
The astrophysical scenario we consider is that of a white dwarfs (WDs) where DM particles annihilate inside the stellar medium so that the metastable mediators produced in the reaction χχ → YY can lose energy while propagating outwards
Summary
Dark matter (DM) accumulation sites can provide a valid strategy to potentially identify hints of DM proper existence as well as its nature and properties. The astrophysical scenario we consider is that of a WD where DM particles annihilate inside the stellar medium so that the metastable mediators produced in the reaction χχ → YY can lose energy while propagating (on-shell) outwards They will decay into photons, Y → γγ, either inside or outside the star, as this is governed by their energy-dependent lifetime and dissipation. If the mediator lifetime is large enough, it could decay outside the stellar radius modifying the expected energy flux value with respect to that arising from decay in central regions In this scenario, medium effects have to be dealt with as, generically, a mediator will loose energy when passing through the ordinary matter, provided the decay length, λD, is larger than the interaction length, λI.
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