KiDS-Legacy: WIMP dark matter constraints from the cross-correlation of weak lensing and Fermi-LAT gamma rays

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Abstract

Dark matter dominates the matter content of the Universe, and its properties can be constrained through large-scale structure probes such as the cross-correlation between the unresolved gamma-ray background (UGRB) and weak gravitational lensing. We analysed 15 years of Fermi–LAT data, constructing UGRB intensity maps in ten energy bins (0.5–1000 GeV), and cross-correlate them with KiDS-Legacy shear in six tomographic bins. The measurements were performed using angular power spectra estimated with the pseudo-$C_\ell$ method. No significant cross-correlation is found. Based on this non-detection, we present 95% upper bounds on the weakly interacting massive particle (WIMP) decay rate $\Gamma_{\rm dec}$ and velocity-averaged annihilation cross-section $\langle\sigma_{\rm ann} v\rangle$ as functions of mass. We compare our results with bounds from other cosmological tracers and from local probes, and found them to be complementary, particularly at low masses ($\rm GeV/TeV$). In addition, using a Euclid-like lensing survey cross-correlated with Fermi–LAT, we forecast $\sim$2 times tighter limits, highlighting the potential of forthcoming data to strengthen constraints on dark matter annihilation and decay.

Left: Upper bounds on the DM thermally averaged cross-section $\left<\sigma_{\rm ann} v\right>$ of high clumping case for the $\tau^+\tau^-$ state, compared to constraints from local probes. This includes results from neutrino detectors such as IceCube (Abbasi et al. 2023) and combined results from ANTARES and IceCube (Albert et al. 2020); the gamma-ray telescope H.E.S.S. (Abdallah et al. 2016), combined results from Fermi-LAT and MAGIC (MAGIC Collaboration 2016); and the red dotted lines represent thermal relic cross-section. Right: Upper bounds on the DM decay rate $\Gamma_{\rm dec}$ for the $\tau^+\tau^-$ state, compared to limits from IceCube (Aartsen et al. 2018) for neutrino surveys, HAWC (Albert et al. 2018) and searches of cosmic rays and the interstellar medium with Fermi-LAT (Ackermann et al. 2012) from gamma-ray telescopes. The cosmological constraints from this work (black solid lines) and work from Paopiamsap et al. (2024) (black dashed lines) are also shown. GC: Galactic centre; dSph: dwarf spheroidal galaxies; Cosmo: cosmological probe.