The Solar Disk at High Energies

Abstract

High energy cosmic rays illuminate the Sun and produce an image that could be observed in up to five different channels: a cosmic-ray shadow (whose energy dependence has been studied by HAWC); a gamma-ray flux (observed at E ≤ 200 GeV by Fermi-LAT); a muon shadow (detected by ANTARES and IceCube); a neutron flux (undetected, as there are no hadronic calorimeters in space); a flux of high energy neutrinos. Since these signals are correlated, the ones already observed can be used to reduce the uncertainty in the still undetected ones. Here we define a simple setup that uses the Fermi-LAT and HAWC observations to imply very definite fluxes of neutrons and neutrinos from the solar disk. In particular, we provide a fit of the neutrino flux at 10 GeV–10 TeV that includes its dependence on the zenith angle and on the period of the solar cycle. This flux represents a neutrino floor in indirect dark matter searches. We show that in some benchmark models the current bounds on the dark matter–nucleon cross section push the solar signal below this neutrino floor.

Monochromatic neutrinos from dark matter through the Higgs portal

“…In addition, CRs reaching the solar surface produce an irreducible neutrino background that defines a floor in DM searches. It has been shown that a capture rate consistent with the current XENON1T bounds implies a neutrino flux from DM annihilations into τ + τ − , JCAP11(2023)068 b b or W + W − already below this floor [9], i.e., these WIMPs should not give any observable signal there.…”

“…We will finally consider the possible signal implied by this model at neutrino telescopes. In particular, we will study whether the signal from DM annihilation in the Sun may be above the background produced by CRs showering in the solar surface [5][6][7][8][9] (in the appendix we provide an approximate fit for this CR background). As the capture rate C = dN cap χ /dt of DM by the Sun depends on the same elastic cross section probed at direct searches, we will consider the maximum coupling c max s /Λ consistent with the bounds from XENON1T.…”

“…On one hand, the same collisions with solar nuclei that capture the WIMP are also probed in direct searches. On the other hand, high energy cosmic rays (CRs) showering in the solar surface produce a flux of neutrinos [5][6][7][8] that, although not observed yet, represents a neutrino floor analogous to the one in direct search experiments [9].…”

Small-scale Magnetic Fields Are Critical to Shaping Solar Gamma-Ray Emission

“…Building on prior theoretical work on the solar-disk gammaray emission (Seckel et al 1991(Seckel et al , 1992Zhou et al 2017;Gutiérrez & Masip 2020;Hudson et al 2020;Li et al 2020;Mazziotta et al 2020;Gutiérrez et al 2022), our model goes much further by considering magnetic fields motivated by solar physics data and magnetoconvection simulations. Our approach introduces the concept of finite-sized flux structures into the problem, differentiating between higher-and lowerenergy proton GCR behaviors by considering two separate flux structures, calculating 3D particle trajectories, and comparing theoretical predictions to data across 3 orders of magnitude in gamma-ray energy.…”

“…The studies by Mazziotta et al (2020) and by Li et al (2020) have integrated the Potential Field Source Surface model of the solar coronal fields into the FLUKA code and implemented numerical simulations of the yields of secondary particles and gamma rays from hadronic GCR showers. Gutiérrez & Masip (2020) and Gutiérrez et al (2022) use HAWC data on the cosmic-ray shadow of the Sun to deduce the averaged hadronic GCR absorption fraction and the gamma-ray yields. Banik et al (2023) present a contrasting perspective, arguing that the acoustic-like shock waves in the chromosphere can accelerate protons in the solar gas up to 10 3 GeV and produce gamma rays that match the HAWC observation.…”