Nonthermal two component dark matter model for Fermi-LAT γ-ray excess and 3.55 keV X-ray line

A two component model of nonthermal dark matter is formulated to simultaneously explain the Fermi-LAT results indicating a gamma-ray excess observed from our Galactic Centre in the 1-3GeV energy range and the detection of an X-ray line at 3.55 keV from extragalactic sources. Two additional Standard Model singlet scalar fields S-2 and S-3 are introduced. These fields couple among themselves and with the Standard Model Higgs doublet H. The interaction terms among the scalar fields, namely H, S-2 and S-3, are constrained by the application of a discrete Z(2) x Z(2)' symmetry which breaks softly to a remnant Z(2)'' symmetry. This residual discrete symmetry is then spontaneously broken through an MeV order vacuum expectation value u of the singlet scalar field S-3. The resultant physical scalar spectrum has the Standard Model like Higgs as chi(1) with M chi(1) similar to 125 GeV, a moderately heavy scalar chi(2) with 50 GeV <= M chi(2) <= 80GeV and a light chi(3) with M chi(3) similar to 7 keV. There is only tiny mixing between chi(1) and chi(2) as well as between chi(1) and chi(3). The lack of importance of domain wall formation in the present scenario from the spontaneous breaking of the discrete symmetry Z(2)'', provided u <= 10 MeV, is pointed out. We find that our proposed two component dark matter model is able to explain successfully both the above mentioned phenomena - the Fermi-LAT observed gamma-ray excess (from the chi(2) -> b (b) over bar decay mode) and the observation of the X-ray line (from the decay channel chi(3) -> gamma gamma) by the XMM-Newton observatory.