Kavli Affiliate: Shunsaku Horiuchi
| Summary:
We revisit the cross-correlation between the unresolved $γ$-ray background and galaxy shapes to constrain the annihilation cross section of particle dark matter. Our analysis uses $γ$-ray photons from 14 years of observations with the Fermi Large Area Telescope (LAT), together with galaxy shape catalogs from the Dark Energy Survey Year 3 (DES Y3) and the Dark Energy Camera All Data Everywhere (DECADE) project, enabling us to probe cosmological large-scale signals over a common sky area of $sim 12,000,mathrmdeg^2$ shared by the $γ$-ray and galaxy data sets. In order to better access signals from large-scale structure, we employ a Fourier-space estimator for the cross-correlation in contrast to the previous DES Y3 analysis. We find that our measurements are consistent with a null detection in a model-independent $χ^2$ test, while template-based analyses yield signals at the $sim 3σ$ level. Our null results exclude an enhanced annihilation cross section for wino-like dark matter with a mass of $2-3$ TeV under a modest substructure boost factor of $sim 30$ in Milky Way-sized halos. For larger boost factors of $sim 100$, the constraints become significantly stronger and exclude the canonical thermal annihilation cross section $langle σv rangle = 3 times 10^-26,mathrmcm^3/mathrms$ for a $7-40$ GeV dark matter particle annihilating into $bbarb$ or $τ^+τ^-$. The template-based analysis favors a power-law $γ$-ray energy dependence of the cross-correlation, but also indicates deviations from that expected based on the mean intensity of the unresolved $γ$-ray background around 100 GeV. We further consider decaying dark matter scenarios and derive $2σ$ lower limits on the particle lifetime of $sim 10^26-10^27,mathrms$, depending on the decay channel.
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