Role of Branching in High-Energy γ-Ray Emission from Dark Matter Annihilation: An Example of the Inert Doublet Model

Understanding the nature of dark matter (DM) and its detection remains one of the most significant unsolved problems in astroparticle physics and cosmology. Considerable efforts have been devoted to the detection of DM through both direct and indirect approaches. Gamma-ray observations offer a powerful probe for the indirect detection of DM. In particular, the spectral features of gamma rays produced through DM interactions are strongly dependent on the underlying annihilation channels into the Standard Model (SM) particles. In this work, we investigate the role of annihilation branching fractions in determining the γ-ray emission from dark matter within the framework of the Inert Doublet Model (IDM). The lightest neutral inert scalar, which serves as a viable DM candidate, can annihilate into various SM particles, including fermions, gauge bosons, and Higgs bosons, depending on DM mass and the model parameters. We analyze how the branching fractions into these final states influence the resulting γ-ray spectra and fluxes. Our study demonstrates that different dominant annihilation channels produce distinct spectral features, significantly affecting the predicted high-energy γ-ray signals. By examining the dependence of γ-ray emission on the branching behavior of DM within IDM, we identify regions of parameter space that can provide better experimental constraints while remaining consistent with the relic density requirements. The results highlight the importance of annihilation branching fractions in interpreting indirect detection signals and provide insights into distinguishing DM within IDM from other weakly interacting massive particles (WIMPs) scenarios. This work underscores the potential of γ-ray observations as a sensitive probe of the IDM parameter space and its underlying annihilation dynamics. Variations in the branching ratios directly influence the resulting γ-ray spectra, thereby affecting the prospects for indirect search of DM with the ground-based γ-ray telescopes such as the Major Atmospheric Cherenkov Experiment (MACE).