Abstract
We explore a two component dark matter model with a fermion and a scalar. In this scenario the Standard Model (SM) is extended by a fermion, a scalar and an additional pseudo scalar. The fermionic component is assumed to have a global mathrm{U(1)}_mathrm{DM} and interacts with the pseudo scalar via Yukawa interaction while a mathbb {Z}_2 symmetry is imposed on the other component – the scalar. These ensure the stability of both dark matter components. Although the Lagrangian of the present model is CP conserving, the CP symmetry breaks spontaneously when the pseudo scalar acquires a vacuum expectation value (VEV). The scalar component of the dark matter in the present model also develops a VEV on spontaneous breaking of the mathbb {Z}_2 symmetry. Thus the various interactions of the dark sector and the SM sector occur through the mixing of the SM like Higgs boson, the pseudo scalar Higgs like boson and the singlet scalar boson. We show that the observed gamma ray excess from the Galactic Centre as well as the 3.55 keV X-ray line from Perseus, Andromeda etc. can be simultaneously explained in the present two component dark matter model and the dark matter self interaction is found to be an order of magnitude smaller than the upper limit estimated from the observational results.
Highlights
Depending upon the production mechanism at the early Universe, the dark matter can be called thermal or nonthermal
Since we are considering a Weakly Interacting Massive particle (WIMP) type dark fermion which interacts with Standard Model (SM) particles via a pseudo scalar mediator and FImP type singlet scalar, we show that our model can evade all the existing stringent bounds on the dark matter (DM)–nucleon spin independent scattering cross-sections
In this work we have explored the viability of a two component dark matter model with a fermionic dark matter that evolves thermally behaving like a WIMP and a non-thermal feebly interacting light singlet scalar dark matter which is produced via the freeze-in mechanism (FImP)
Summary
Depending upon the production mechanism at the early Universe, the dark matter can be called thermal or nonthermal. In order to explain the Galactic Centre gamma ray excess and DM self interaction bound from colliding galaxy clusters in a single framework of particle dark matter scenario, we propose a two component dark matter model where the Standard Model is extended by adding one extra singlet scalar and a fermion. We find that besides satisfying the relic density criterion and other relevant experimental bounds, the annihilation of the dark fermion to the bb (through pseudo scalar mediator) final state at the Galactic Centre can explain the Fermi-LAT observed gamma ray excess while self interaction of light FImP dark matter is consistent with the upper bound on the DM self interaction required to explain the spatial offset in the collision of different galaxy clusters as obtained from [132,133] and appears to be smaller by at least an order of magnitude.
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