Constraining dark matter using 20-year INTEGRAL/IBIS observations II: Sub-GeV dark matter

Abstract

We present new constraints on sub-GeV dark matter (DM) annihilation and decay using twenty years of diffuse hard X-ray observations from the INTEGRAL/IBIS telescope. By performing a joint analysis of the spectral and morphological information contained in the IBIS dataset, we simultaneously fit Galactic longitudinal profiles and energy spectra, exploiting their complementary signatures to disentangle potential DM signals from the dominant astrophysical backgrounds. We use physically motivated background models combining inverse-Compton (IC) emission from Galactic cosmic-ray electrons with thermal emission from unresolved accreting white dwarfs, and consistently include the secondary IC emission generated by DM-induced electron and positron populations propagated through the Galaxy. We conservatively derive 95% upper limits on the annihilation cross section $\langleσv\rangle$ and decay half-life $τ$ for the $e^+e^-$, $μ^+μ^-$, and $π^+π^-$ final states across the mass range 1 MeV to 5 GeV. Our constraints are in the range $10^{-28}$ cm$^3$/s $\lesssim \langleσv\rangle \lesssim 10^{-26}$ cm$^3$/s for annihilation and $τ\gtrsim 10^{25}$ s for decay at DM masses of a few MeV, improving upon existing X-ray limits by up to two orders of magnitude over much of the mass range. Our bounds are translated into constraints on the kinetic mixing parameter $ε$ of a dark photon and the scalar-Higgs mixing angle $\sinθ$, and compared with existing indirect, direct and accelerator limits available, providing a comprehensive picture of the allowed parameter space for light portal DM.