Confronting galactic and extragalactic γ-rays observed by Fermi-lat with annihilating dark matter in an inert Higgs doublet model

In this thorough study, we focus on the indirect detection of dark matter (DM) through the examination of unexplained galactic and extragalactic γ-ray signatures for a low-mass DM model. For this purpose, we consider a simple Higgs-portal DM model, namely, the inert Higgs doublet model (IHDM) where the SM is extended with an additional complex SU(2)_L doublet scalar. The stability of the DM candidate in this model, i.e., the lightest neutral scalar component of the extra doublet, is ensured by imposing discrete $Z_2$ symmetry. The reduced-${\chi }^2$ analysis using theoretical, experimental, and observational constraints suggests that the best-fit value of DM mass in this model is ∼63.5 GeV. We analyze the anomalous GeV γ-ray excess from the Galactic Center in light of the best-fit IHDM parameters. We further check the consistency of the best-fit IHDM parameters with the Fermi Large Area Telescope (Fermi-LAT) obtained limits on photon flux for 18 Milky Way dwarf spheroidal satellite galaxies (dSphs) known to be mostly dominated by DM. Also, since the γ-ray signal from DM annihilation is assumed to be embedded within the extragalactic γ-ray background (EGB), the theoretical calculations of photon flux for the best-fit parameter point in the IHDM framework are compared with the Fermi-LAT results for diffuse and isotropic EGB for different extragalactic and astrophysical background parametrizations. We show that the low-mass DM in the IHDM framework can satisfactorily account for all of the observed continuum γ-ray fluxes originating from galactic and extragalactic sources. The extensive analysis performed in this work is valid for any Higgs-portal model with DM mass comparable to that considered in this work.