Searching for dark matter annihilating into light long-lived mediators from stars inside dwarf spheroidal galaxies

TL;DR

This study investigates dark matter annihilation into long-lived mediators in dwarf spheroidal galaxies using 16 years of Fermi-LAT data, setting new constraints on DM properties and comparing with direct detection bounds.

Contribution

It introduces a novel indirect detection method focusing on long-lived mediators from dwarf spheroidal galaxies and incorporates Sommerfeld enhancement into the analysis.

Findings

Set upper limits on DM-nucleon scattering cross section (~10^{-36} cm^2 at 100 GeV)

Analyzed 16 years of Fermi-LAT data for DM signals

Compared results with direct detection experiment bounds

Abstract

Several astrophysical and cosmological observations suggest the existence of dark matter (DM) through its gravitational effects, yet its nature remains elusive. Despite the lack of DM signals from direct detection experiments, efforts continue to focus on the indirect detection of DM from DM-rich astrophysical objects. Dwarf spheroidal galaxies (dSphs) are among the most promising targets for such searches. In this work, we aim to investigate the expected DM capture rate from the stellar component of ten nearby DM-rich dSphs, assuming that the accumulated DM eventually annihilates into light, long-lived mediators (LLLMs) which decay into gamma rays outside the dSphs. We analyze nearly 16 years of {\it Fermi}-LAT data to search for DM annihilation through LLLMs, and, from the observed stacked flux upper limits, set limits on the DM-nucleon scattering cross section for the case of a generic DM scenario. Additionally, we incorporate the Sommerfeld enhancement (SE) effect into the DM annihilation process assuming scalar DM model, and obtain bounds on the DM-nucleon scattering cross section of $\sim~10^{-36} {\rm cm}^2$ for DM masses around 100 GeV. This allows us to explore an alternative avenue for exploring DM phenomena from dSphs and compare our results with the bounds reported by direct DM detection experiments and other celestial bodies.