A potentially detectable gamma-ray line in the Fermi Galactic center excess — in light of one-step cascade annihilations of secluded (vector) dark matter via the Higgs portal

Abstract

We show the presence of a potentially detectable gamma-ray line in the Fermi Galactic center excess in light of the secluded (vector) dark matter (DM) model in which the hidden scalar, nearly degenerate with DM in mass, mediates the interaction of the secluded DM with the Standard Model (SM) due to its mixing with the SM Higgs. We find that the parameter region m X ∈ [60, 132] GeV can provide a good fit to the Fermi Galactic center gamma-ray excess spectrum, appearing a prominent gamma-ray line with the energy ∈ [30, 66] GeV. The best fit gives m X m S 86 GeV with a p-value = 0.42, so that the resultant gamma-ray line, arising from the decay of the scalar mediator into γγ, peaks at 43 GeV. We derive constraints on the annihilation cross section from the Fermi-LAT gamma-ray line search, gamma-ray observations of the Fermi-LAT dwarf spheroidal galaxies, and Planck cosmic microwave background measurement. For the secluded vector DM model, the parameter space constrained by the current XENON1T and future LUX-ZEPLIN is shown. Finally, for the mixing angle between the Higgs sectors, we discuss its lower bound, which is required by the big bang nucleosynthesis constraint and relevant to the hidden sector decoupling temperature.

Neutrino Portal to FIMP Dark Matter with an Early Matter Era

“…Nevertheless, space and ground-based telescopes can place stringent bounds on the dark matter annihilation cross-section and lifetime (see [84] for a recent review). In our case, if dark matter is heavier than the heavy neutrino (m DM > m N ), it may annihilate into heavy neutrinos that further decay into SM particles (νh, νZ, l ± W ∓ , l ± W ∓ γ, ννν, νl + l − ) [85][86][87][88], generating neutral and charged cosmic rays after hadronization and parton showers. In particular, over the past years, excesses of gamma-rays has been observed by several experiments, including INTEGRAL/SPI [89], Fermi-LAT [90] and H.E.S.S.…”

Indirect Searches for Secluded Dark Matter

“…Secluded scenarios were overly studied in the literature in context of the galactic center excess [17,18]. Another interesting indirect signature is provided by the search for DM signals at planets and stars [11,12], in these cases, when the DM annihilates directly into SM particles the only final state we can observe from indirect searches is an attenuated neutrino signal, because the other SM channels are trapped by the environment inside the stars/planets, however, if the DM annihilates into metastable mediators (with an enough decay rate), they can easily escape from the surface's planet/star, and its subsequently decay into SM particles leaves interesting indirect signatures [9], including into gamma rays.…”

Indirect Searches for Secluded Dark Matter

“…Secluded scenarios were overly studied in the literature in context of the galactic center excess [17,18]. Another interesting indirect signature is provided by the search for DM signals at planets and stars [11,12], in these cases, when the DM annihilates directly into SM particles the only final state we can observe from indirect searches is an attenuated neutrino signal, because the other SM channels are trapped by the environment inside the stars/planets.…”