A search for dark matter cosmic-ray electrons and positrons from the Sun with the Fermi Large Area Telescope

Abstract: We use 7 years of electron and positron Fermi-LAT data to search for a possible excess in the direction of the Sun in the energy range from 42 GeV to 2 TeV. In the absence of a positive signal we derive flux upper limits which we use to constrain two different dark matter (DM) models producing $e^+ e^-$ fluxes from the Sun. In the first case we consider DM model being captured by the Sun due to elastic scattering and annihilation into $e^+ e^-$ pairs via a long-lived light mediator that can escape the Sun. In the second case we consider instead a model where DM density is enhanced around the Sun through inelastic scattering and the DM annihilates directly into $e^+ e^-$ pairs. In both cases we perform an optimal analysis, searching specifically for the energy spectrum expected in each case, i.e., a box-like shaped and line-like shaped spectrum respectively. No significant signal is found and we can place limits on the spin-independent cross-section in the range from $10^{-46}~cm^2$ to $10^{-44}~cm^2$ and on the spin-dependent cross-section in the range from $10^{-43}~cm^2$ to $10^{-41}~cm^2$. In the case of inelastic scattering the limits on the cross-section are in the range from $10^{-43}~cm^2$ to $10^{-41}~cm^2$. The limits depend on the life time of the mediator (elastic case) and on the mass splitting value (inelastic case), as well as on the assumptions made for the size of the deflections of electrons and positrons in the interplanetary magnetic field.

• The paper presents an analysis of seven years of Fermi-LAT data to search for cosmic-ray electron and positron signals from the Sun linked to dark matter.
• It compares two dark matter interaction models—elastic scattering with long-lived mediators producing a box-like spectrum and inelastic scattering yielding a line-like feature.
• The study sets upper limits on DM-nucleon cross-sections, narrowing the parameter space and complementing constraints from experiments like PICO-60 and XENON1T.

An Analysis of Dark Matter-Induced Cosmic-Ray Electrons and Positrons from the Sun Using Fermi-LAT Data

The search for dark matter (DM) has prompted numerous studies aiming to detect indirect signatures of DM annihilation or decay. The paper "A search for dark matter cosmic-ray electrons and positrons from the Sun with the Fermi Large Area Telescope" focuses on utilizing seven years of data from the Fermi Large Area Telescope (Fermi-LAT) to investigate potential excesses of cosmic-ray electrons and positrons (CREs) emanating from the direction of the Sun. This study leverages the absence of positive signals to impose constraints on two theoretical models of DM interactions.

The research hypothesizes two distinct DM models. The first model investigates elastic scattering within the Sun, leading to DM capture, subsequent annihilation, and decay via a long-lived light mediator that escapes the Sun. This results in a predicted box-like energy spectrum of CREs detectable by instruments like Fermi-LAT. The second model explores inelastic scattering, anticipating direct DM annihilation into electron-positron pairs, manifesting as a line-like spectral feature at Earth.

The observational data spans an energy range from 42 GeV to 2 TeV. No significant CRE signals were observed emanating from the Sun, thus leading the researchers to establish upper limits on the DM-nucleon scattering cross-section. The limits on the spin-independent cross-section range from approximately $10^{-46} \text{cm}^2$ to $10^{-44} \text{cm}^2$, whereas the spin-dependent cross-section constraints fall between $10^{-43} \text{cm}^2$ and $10^{-41} \text{cm}^2$. The determination of these limits varies depending on model parameters, such as the lifetime of the mediator and the mass splitting scenario.

This study's results illustrate the utility of the Fermi-LAT data in constraining DM models, aligning with constraints from other contemporary particle physics experiments like PICO-60 and XENON1T. They highlight that while DM-induced CRE production from the Sun is not supported by current data, the derived constraints remain competitive particularly in scenarios involving long-lived mediators and high DM masses.

The implications of this research are pivotal in narrowing down viable DM models and providing a comparative framework for future experiments. Systematic methods combined with complementary observations are essential in advancing the field of DM research. Future developments in detector sensitivity and analytical techniques might further refine these limits or potentially identify the elusive signals of DM interactions, enhancing our understanding of the most enigmatic component of cosmology.

The thorough evaluation performed in this study reflects a significant contribution to the ongoing endeavor to unveil the nature of dark matter, reiterating the crucial role of indirect detection strategies in astroparticle physics.