The Fermi–LAT Galactic Center Excess: Evidence of Annihilating Dark Matter?

Abstract

The center of the Galaxy is one of the prime targets in the search for a signal of annihilating (or decaying) dark matter. If such a signal were to be detected, it would shed light on one of the biggest mysteries in physics today: What is dark matter? Fundamental properties of the particle nature of dark matter, such as its mass, annihilation cross section, and annihilation final states, could be measured for the first time. Several experiments have searched for such a signal, and some have measured excesses that are compatible with it. A long-standing and compelling excess is observed in γ-rays by the Fermi Large Area Telescope ( Fermi–LAT). This excess is consistent with a dark matter particle with a mass of approximately 50 (up to ∼200) GeV annihilating with a velocity-averaged cross section of ∼10−26 cm3 s−1. Although a dark matter origin of the excess remains viable, other interpretations are possible. In particular, there is some evidence that the excess is produced by a population of unresolved point sources of γ-rays—for example, millisecond pulsars. In this article, I review the current status of the observation of the Fermi–LAT Galactic center excess, the possible interpretations of the excess, the evidence and counterevidence for each, and the prospects for resolving its origin with future measurements.

Amplified J-factors in the Galactic Center for velocity-dependent darkmatter annihilation in FIRE simulations

“…An observed excess in gamma-ray emission from the Galactic Center based on Fermi Large Area Telescope observations has sparked considerable interest as a potential indirect detection signal (Hooper & Goodenough 2011;Abazajian & Kaplinghat 2012;Martin et al 2014;Ajello et al 2016;Ackermann et al 2017). The basic excess has been confirmed by multiple groups (see Murgia 2020, for a review) and is consistent with expectations for a dark matter particle with mass 𝑚 𝜒 ∼ 10 − 100 GeV annihilating with a velocity-averaged cross section that matches the thermal WIMP expectation. A different signal from the Andromeda galaxy halo is potentially consistent with this interpretation (Karwin et al 2020).…”

Dim but not entirely dark: Extracting the Galactic Center Excess' source-count distribution with neural nets

“…A promising avenue, which complements collider searches and direct detection efforts, is indirect detection: the search for standard model particles resulting from the decay or annihilation of DM. An unexplained excess of γ-ray emission from the Galactic Center region in the data of the Fermi space telescope, peaked at ∼ 1 − 3 GeV, has attracted much interest as it seems to be generally consistent with a signal originating from annihilating DM (for a recent review, see Murgia [3]). This so-called Galactic Center Excess (GCE) extends ∼ 10 • outwards from the Galactic Center and broadly follows the spatial profile expected for pair annihilation in a generalized NFW halo [4,5].…”

Jets and photons spectroscopy of Higgs-ALP interactions

“…Effective operators of ALP-gluons and ALP-photons are generally expected to be generated at the one-loop level in ultra-violet completed theories, where couplings with new heavy charged and colored fermions ψ occur through renormalizable operators like iy a ψγ 5 ψ. In the case of ALPs, besides their probable role in the solutions to unanswered questions in particle physics, light axions/ALPs extend their scope to other observed anomalies if we consider, for example, couplings to photons and leptons that might explain the 4.2σ discrepancy of the (g − 2) µ data [19], the excess in excited Beryllium decays [20], and the excess in the gamma rays flux from the center of the galaxy observed by Fermi-LAT [21,22], for instance.…”