Constraining dark matter annihilation with the isotropicγ-ray background: Updated limits and future potential

Abstract

The nature of the isotropic γ-ray background (IGRB) measured by the Large Area Telescope (LAT) on the Fermi γ-ray space telescope (Fermi) remains partially unexplained. Non-negligible contributions may originate from extragalactic populations of unresolved sources such as blazars, star-forming galaxies or galactic millisecond pulsars. A recent prediction of the diffuse γ-ray emission from active galactic nuclei (AGN) with a large viewing angle with respect to the line of sight has demonstrated that this faint but numerous population is also expected to contribute significantly to the total IGRB intensity. A more exotic contribution to the IGRB invokes the pair annihilation of dark matter (DM) weakly interacting massive particles (WIMPs) into γ rays. In this work, we evaluate the room left for galactic DM at high latitudes (> 10 ∘ ) by including photons from both prompt emission and inverse Compton scattering, emphasizing the impact of the newly discovered contribution from misaligned AGN (MAGN) for such an analysis. Summing up all significant galactic and extragalactic components of the IGRB, we find that an improved understanding of the associated astrophysical uncertainties is still mandatory to put stringent bounds on thermally produced DM. On the other hand, we also demonstrate that the IGRB has the potential to be one of the most competitive future ways to test the DM WIMP hypothesis, once the present uncertainties are even slightly reduced. In fact, if MAGN contribute even at 90% of the maximal level consistent with our current understanding, thermally produced WIMPs would be severely constrained as DM candidates for masses up to several TeV.

Indirect detection of dark matter with γ rays

“…The most conservative approach when calculating upper limits on the dark matter annihilation interaction rate is to assume that all of the IGRB is caused by dark matter annihilation. When making rather conservative assumptions about the contribution of source populations to the IGRB dark matter annihilation interaction, rate limits can be derived (57)(58)(59)(60) that are competitive with other methods, such as dwarf spheroidal galaxies. Obviously, these limits can be significantly tightened when including additional source populations; however, the degree to which the contribution from such classes can be determined is questionable.…”

Fluctuations of the gravitational field generated by a random population of extended substructures

“…Current observational efforts to test the presence of dark subhaloes in the Milky Way range from searching for gammaray annihilation signals (e.g. Ackermann et al 2014;Bringmann et jorpega@roe.ac.uk al. 2014) to detecting gaps in narrow tidal streams induced by close encounters with individual subhaloes (Ibata et al 2002;Johnston et al 2002;Yoon et al 2011;Carlberg 2013;Erkal & Belokurov 2015;Ngan et al 2016, Erkal et al 2016Bovy et al 2017), with no unambiguous results to date.…”

AMS02 positron excess from decaying fermion DM with local dark gauge symmetry

“…Assuming its DMorigin, 1 this excess can be explained by annihilating DM with thermally-averaged cross section σ v ∼ 10 −23 cm 3 /s, or decaying DM with lifetime τ = Γ −1 ∼ 10 26 s. It is also well known that for annihilating DM a large boost factor ∼10 3 [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] is needed to fit the positron spectra. However, such a large boost factor is strongly constrained by the CMB data [29][30][31][32][33] and Fermi/LAT gamma-ray measurements [34][35][36][37][38][39][40]. On the other hand, O(TeV) DM decaying into leptons [41][42][43][44][45][46][47][48][49][50] can give a consistent explanation without conflict with such stringent constraints, especially for DM decay into the μ + μ − channel.…”