Abstract
We point out that 7 keV axino dark matter (DM) in the R-parity violating (RPV) supersymmetric (SUSY) Dine-Fischler-Srednicki-Zhitnitsky model can simultaneously reproduce the 3.5keV X-ray excess, and evade stringent constraints from the Ly-alpha forest data. Peccei-Quinn symmetry breaking naturally generates both axino interactions with minimal SUSY standard model particles and RPV interactions. The RPV interaction introduces an axino-neutrino mixing and provides axino DM as a variant of sterile neutrino DM, whose decay into a monochromatic photon can be detected by X-ray observations. Axinos, on the other hand, are produced by freeze-in processes of thermal particles in addition to the Dodelson-Widrow mechanism of sterile neutrinos. The resultant phase space distribution tends to be colder than the Fermi-Dirac distribution. The inherent entropy production from late-time saxion decay makes axinos even colder. The linear matter power spectrum satisfies even the latest and strongest constraints from the Ly-alpha forest data.
Highlights
An anomalous 3.5 keV line excess in the XMM-Newton and Chandra x-ray spectra of the Andromeda galaxy and galaxy clusters was first reported by two independent groups [1]
We show that freeze-in 7 keV axino dark matter (DM) is concordant with the current constraints from the Ly-α forest data
We have proposed 7 keV axino DM in the R-parity violating (RPV) SUSY DFSZ axion model as a variant of the sterile neutrino DM explaining the 3.5 keV x-ray line excess
Summary
An anomalous 3.5 keV line excess in the XMM-Newton and Chandra x-ray spectra of the Andromeda galaxy and galaxy clusters was first reported by two independent groups [1]. The axino mass is of order of keV in some models [10], it is naively of order of the gravitino mass since it is generated by the SUSY breaking In this model, the Peccei-Quinn (PQ) symmetry breaking at vPQ ∼ 1010 GeV simultaneously generates the TeV-scale μ term via the Kim-Nilles mechanism [11] and MeV-scale bilinear R-parity violating (bRPV) term [12]. This is a well-known solution to μ-term generation by the Kim-Nilles mechanism [11] From this interaction, freeze-in production of axinos occurs dominantly when the cosmic temperature (T) is of order of the mass of the other SUSY particle involved in the process [21,22,23]. MavPQ ð5Þ where vu is the VEV of Hu and mais the axino mass
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