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

TL;DR

This work probes WIMP dark matter by cross-correlating the unresolved gamma-ray background with KiDS-Legacy weak-lensing maps, using 15 years of Fermi-LAT data across 10 energy bins and six lensing tomographic bins. No significant cross-correlation is detected, enabling 95% confidence upper bounds on the DM annihilation cross-section $\langle\sigma_{ann}v\rangle$ and decay rate $\Gamma_{dec}$ as functions of $m_{DM}$ for $b\bar{b}$, $\mu^+\mu^-$, and $\tau^+\tau^-$ final states, with comparisons to other cosmological and local probes. The analysis incorporates a blazar-dominated UGRB model, a halo-model description of the signal, and combined covariances from jackknife and NaMaster, highlighting complementary sensitivity to low-mass DM. Forecasts for a Euclid-like survey suggest about a factor of two tighter constraints, driven by larger sky coverage and deeper lensing data, though gamma-ray PSF and photon counts limit improvements at present. Overall, cosmological cross-correlation provides a robust, complementary avenue to constrain DM properties and will become increasingly powerful with upcoming wide-area surveys and better astrophysical modelling.

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-correlated 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 $Γ_{\rm dec}$ and velocity-averaged annihilation cross-section $\langleσ_{\rm ann} v\rangle$ 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.

Figures (13)

• Figure 1: Top: redshift distributions of the KiDS-Legacy gold-selected sample for tomographic bins, where the photometric redshift bin with $z$ in $[0.1, 2.0]$ is the sum weighted by the effective number densities listed in Table \ref{['Tab:shape_noise']}. The shaded vertical bands indicate the boundaries of the tomographic photometric redshift bins. Bottom: weak lensing window functions for six tomographic bins in KiDS-Legacy.
• Figure 2: The window functions for gamma-rays produced by DM annihilation, decay, and astrophysical sources across an energy range of $0.5-1000\rm~GeV$. The annihilation process assumes $\left<\sigma_{\rm ann} v\right>=3\times10^{-26} \rm ~cm^{3}s^{-1}$steigman2012precise, where the three scenarios are considered: high (purple), mid (orange), low (green), representing different amounts of DM concentration for subhaloes. The DM decay (black) assumes a particle decay rate of $\Gamma_{\rm dec} = 5\times10^{-28}~\rm s^{-1}$, taken as a representative benchmark consistent with current limits. Both processes are modelled with the assumption of the final state in $b\bar{b}$ pairs and $m_{\rm DM}=100~\rm GeV$ for this figure. The contribution from unresolved blazars, which were taken as the only astrophysical source of the UGRB in this analysis, is shown in pink.
• Figure 3: Model of $C^{\rm g\kappa}_{\ell}$ for three clumping cases of DM annihilation, decaying DM, and astrophysical background. The models and formatting are the same as in Fig. \ref{['Fig: g_window']}. The models assumed the redshift $n(z)$ for $z$ in the range of $[0.1, 2.0]$ and energy range from 0.5 to 1000 GeV. The effect of the Fermi-LAT PSF was not considered. The blazar component shown in pink represents the unresolved blazar contribution to the astrophysical background adopted in this analysis.
• Figure 4: Halo model of the power spectrum of gamma-ray contributions from DM annihilation and shear cross-correlation at $z=0$. The blue dash–dotted and green dotted curves show the one-halo and two-halo terms, respectively; the red dashed curve is their summation, and the black solid curve shows the power spectrum fitted with halofit at $z=0$.
• Figure 5: The Fermi PSF in harmonic space $b_\ell$ in ten different energy bins. It shows an inverse relationship between the energy and the suppression of the PSF effect. The black dashed line represents $\ell = 1500$, referring to the upper limit of $\ell$ in the cross-power spectrum measurement.