The Sun at GeV--TeV Energies: A New Laboratory for Astroparticle Physics

TL;DR

This paper discusses the Sun as a new laboratory for astroparticle physics, highlighting recent gamma-ray observations revealing unexpected phenomena that challenge existing models and offer insights into cosmic rays and dark matter.

Contribution

It introduces the potential of GeV--TeV gamma-ray observations of the Sun over a solar cycle to advance understanding of solar environment and particle physics.

Findings

Detection of a hard gamma-ray excess anti-correlated with solar activity

Existing models cannot fully explain the observed gamma-ray properties

Observations across a solar cycle can shed light on cosmic-ray interactions and dark matter

Abstract

The Sun is an excellent laboratory for astroparticle physics but remains poorly understood at GeV--TeV energies. Despite the immense relevance for both cosmic-ray propagation and dark matter searches, only in recent years has the Sun become a target for precision gamma-ray astronomy with the Fermi-LAT instrument. Among the most surprising results from the observations is a hard excess of GeV gamma-ray flux that strongly anti-correlates with solar activity, especially at the highest energies accessible to Fermi-LAT. Most of the observed properties of the gamma-ray emission cannot be explained by existing models of cosmic-ray interactions with the solar atmosphere. GeV--TeV gamma-ray observations of the Sun spanning an entire solar cycle would provide key insights into the origin of these gamma rays, and consequently improve our understanding of the Sun's environment as well as the foregrounds for new physics searches, such as dark matter. These can be complemented with new observations with neutrinos and cosmic rays. Together these observations make the Sun a new testing ground for particle physics in dynamic environments.