Energy peak: Back to the Galactic Center GeV gamma-ray excess

Abstract

We propose a novel mechanism enabling us to have a continuum bump as a signature of gammaray excess in indirect detection experiments of dark matter (DM), postulating a generic dark sector having (at least) two DM candidates. With the assumption of non-zero mass gap between the two DM candidates, the heavier one directly communicates to the partner of the lighter one. Such a partner then decays into a lighter DM particle along with an "axion-like" particle (ALP) or dark "pion", which subsequently decays into a pair of photons, via a more-than-one step cascade decay process. Since the cascade is initiated by the dark partner obtaining a non-trivial fixed boost factor, a continuum γ-ray energy spectrum naturally arises even with a particle directly decaying into two photons. We apply the main idea to the energy spectrum of the GeV γ-rays from around the Galactic Center (GC), and find that the relevant observational data is well-reproduced by the theory expectation predicted by the proposed mechanism. Remarkably, the relevant energy spectrum has a robust peak at half the mass of the ALP or dark pion, as opposed to popular DM models directly annihilating to Standard Model particles where physical interpretations of the energy peak are not manifest. Our data analysis reports substantially improved fits, compared to those annihilating DM models, and ∼ 900 MeV mass of the ALP or dark pion.

Energy spectra of massive two-body decay products and mass measurement

“…7 Finally, the energy-peak observation was applied to interpret the Galactic Center GeV gamma-ray excess in ref. [83].…”

“…[71] for more details). This function has been tested in the context of i) bottom quark energy spectrum from the decay of SM top quark at LHC-7 TeV [71] and b-jets (including higher order QCD corrections) at LHC-14 TeV [78]; ii) a gluino cascade decay [76]; iii) the mass determination of KK graviton [82], and iv) a DM interpretation for the Galactic Center GeV gamma-ray excess [83].…”

Boxes, boosts, and energy duality: Understanding the Galactic Center gamma-ray excess through Dynamical Dark Matter

“…[40,50,[52][53][54][55] within the context of collider phenomenology, and in Refs. [41,51] within the context of gamma-ray astrophysics. Of course, while the current data describing the GC excess is consistent with a sharp peak, it is also consistent with a narrow plateau or smoothly rounded maximum, provided the width of the bump is less than the resolution of the binning.…”

“…While a spectrum with these duality properties can be realized in certain cascade-based models [41], we shall show that a self-dual gamma-ray spectrum also has a natural interpretation within the Dynamical Dark Matter (DDM) framework [42,43]. Indeed, as we shall show, there exists a simple class of DDM models which yield an energy-dual spectrum that provides an excellent fit to the Fermi-LAT data, with a self-dual energy E Ã ∼ Oð1 GeVÞ.…”

Energy peaks: A high energy physics outlook

“…At variance with the scenario of direct Dark Matter annihilation or decay into SM states, in Refs. [38,39] it has been proposed that bump-like features of the excess gamma rays spectra can originate from multi-particle Dark Matter sectors through decays χ → φχ followed by φ → γγ for mass m φ around twice the energy of the peak region of the excess. The spectral shape of this type of signal is in direct connection with properties of the Dark Matter sector, hence allows to test more directly the models of Dark Matter and in some cases it has been shown to give better fits to the reported excess data [38,39].…”