X-ray line from exciting dark matter

Abstract

The eXciting Dark Matter (XDM) model was proposed as a mechanism to efficiently convert the kinetic energy (in sufficiently hot environments) of dark matter into e+e-pairs. The standard scenario invokes a doublet of nearly degenerate DM states, and a dark force to mediate a large upscattering cross section between the two. For heavy (∼ TeV) DM, the kinetic energy of WIMPs in large (galaxy-sized or larger) halos is capable of producing low-energy positrons. For lighter dark matter, this is kinematically impossible, and the unique observable signature becomes an X-ray line, arising from χχ → χ * χ * , followed by χ * → χγ. This variant of XDM is distinctive from other DM X-ray scenarios in that its signatures tend to be most present in more massive, hotter environments, such as clusters, rather than nearby dwarfs, and has different dependencies from decaying models.We find that it is capable of explaining the recently reported X-ray line at 3.56 keV. For very long lifetimes of the excited state, primordial decays can explain the signal without the presence of upscattering. Thermal models freeze-out as in the normal XDM setup, via annihilations to the light boson φ. For suitable masses the annihilation χχ → φφ followed by φ → SM can explain the reported gamma-ray signature from the galactic center. Direct detection is discussed, including the possibility of explaining DAMA via the "Luminous" dark matter approach. Quite generally, the proximity of the 3.56 keV line to the energy scale of DAMA motivates a reexamination of electromagnetic explanations. Other signals, including lepton jets and the modification of cores of dwarf galaxies are also considered.PACS numbers: 95.35.+d

(O)Mega split

“…However, since the initial excitement there have been challenges to the decaying dark matter interpretation [36][37][38], including from the non-observation of the line in stacked dwarf spheroidal galaxies [39] and other stacked galaxies [40] despite its observation in the Milky Way [41]. Perhaps the most plausible explanations that avoid these issues are excited dark matter [42][43][44][45][46] and an dark matter decaying to an axion-like particle in the magnetic field of a cluster [47][48][49][50][51]. On the other hand, the decaying dark matter explanation is not yet completely excluded, and so in this appendix we shall describe how a class of models related to the FSSM provides an explanation for the line.…”

3.5 keV X-ray line signal from dark matter decay in local U(1)B−L extension of Zee-Babu model

“…And we (almost) neglect their mixings. 5 In other words h, φ and n are considered as mass eigenstates with masses m h , m φ and m n . From (2.…”

“…11) 5 We will allow, however, small mixing between H and η, when we consider the decay of n. 6 There is also small contribution from ηψiψi interactions in the diagonal part. But since vη ∼ 10 − 100 MeV, they are small and we absorb them to m ψ i .…”

Detecting fluorescent dark matter with X-ray lasers

“…The 3.5 keV line observed in the diffuse emission from galaxy clusters in such a situation arises from fluorescent re-emission. Similar models have been considered previously, for example in [17,19,23,24]. In particular [19] uses a more general version of the model given in Eq.…”

“…The origin of this line could also be the decay of dark matter, in which case the mass of the dark matter particle is typically double the energy of the emitted photon. Another interpretation of this line is that it might correspond to the energy gap between a ground and excited state of dark matter [17][18][19][20]. In that situation, one would expect emission and/or absorption at that particular frequency, depending upon the situation.…”