Can a millicharged dark matter particle emit an observable γ-ray line?

Abstract

If a γ-ray line is observed in the near future, it will be important to determine what kind of dark matter (DM) particle could be at its origin. We investigate the possibility that the γ-ray line would be induced by a slow DM particle decay associated to the fact that the DM particle would not be absolutely neutral. A "millicharge" for the DM particle can be induced in various ways, in particular from a kinetic mixing interaction or through the Stueckelberg mechanism. We show that such a scenario could lead in specific cases to an observable γ-ray line. This possibility can be considered in a systematic modelindependent way, by writing down the corresponding effective theory. This allows for a multi-channel analysis, giving in particular upper bounds on the intensity of the associated γ-ray line from cosmic rays emission. Our analysis includes the possibility that in the twobody decay the photon is accompanied with a neutrino. We show that, given the stringent constraints which hold on the millicharge of the neutrinos, this is not an option, except if the DM particle mass lies in the very light KeV-MeV range, allowing for a possibility of explanation of the recently claimed, yet to be confirmed, ∼ 3.5 KeV X-ray line.

X-ray lines fromR-parity violating decays of keV sparticles

“…(1) Some potential models have been proposed which might account for this observational anomaly [1,[3][4][5][6][7][8][9][10][11][12][13][14][15][16], the possibility of decaying sterile neutrinos or axions receiving particular attention. Given the wide expectation that SUSY should play a leading role in physics beyond the Standard Model, it is interesting to explore possible SUSY explanations for this signal.…”

SUSY in the sky or a keV signature of sub-GeV gravitino dark matter

“…Comparing Eqs. (12) and (13) one can see that production of gravitinos is more effective and when mass density of gravitinos is sufficient to explain the dark matter the abundance of sgoldstino is quite small: they form a subdominant fraction of the dark matter. Fraction ǫ ≡ Ω P /Ω 3/2 of produced sgoldstino checks with what constraint (4) gives if…”

“…Although the observation has significance only at (3σ − 4σ) level and its explanation in the framework of known physics is possible it would be very exciting if the source of this line is in new physics probably related to so far elusive dark matter. Various scenarios have been studied including sterile neutrinos [3,4,5], XDM model [6,7], axion-like particles [8,9,10,11,12], millicharged particles [13] and light inflaton [14]. Below we are interested in possible explanations of this phenomena in the framework of supersymmetric theories.…”

Dipolar dark matter in light of the 3.5 keV x-ray line, neutrino mass, and LUX data

“…The recently observed 3.5 keV X-ray line signal in the spectrum of 73 galaxy clusters as reported by the XMM-Newton X-ray observatory [6,7] will provide a strong hint for nongravitational Dark Matter interaction if confirmed by others. A few attempts have been already taken in order to explain this excess of X-ray signal by (i) decaying dark matter or annihilating dark matter, [8][9][10][11][12][13][14][15][16][17][18][19][20], (ii) magnetic dipolar dark matter (via upscattering of dark matter into an excited states and subsequent decay of excited states into dark matter and an X-ray photon), [21][22][23][24][25][26][27], (iii) others . From the recent explored scenarios it is found that such a photon signal, if the claimed excess persists, can be explained by late decay and/or annihilation of multi-keV mass dark matter, or decay of a second lightest metastable particle to lightest stable particle with a keV mass splitting.…”