The Sun as a sub-GeV dark matter accelerator

Timon Emken,Chris Kouvaris,Niklas Grønlund Nielsen

doi:10.1103/physrevd.97.063007

Abstract

Sub-GeV halo dark matter that enters the Sun can potentially scatter off hot solar nuclei and be ejected much faster than its incoming velocity. We derive an expression for the rate and velocity distribution of these reflected particles taking into account the Sun's temperature and opacity. We further demonstrate that future direct detection experiments could use these energetic reflected particles to probe light dark matter in parameter space that cannot be accessed via ordinary halo dark matter.

Highlights

Despite convincing astrophysical evidence for the existence of dark matter (DM) in the Universe, the numerous direct-detection experiments set out to observe DM on Earth have not yet succeeded, severely constraining the classic weakly interacting massive particle (WIMP) paradigm [1,2,3]
Detectors with targets of mass mT and energy threshold Eth capn,ffiffiffiffiffiiffinffiffiffiffiffiffipffiffirffiffiiffinffiffifficffiffiiffipffi le, probe DM masses down to ∼mT/ð 2mTv2max/Eth − 1Þ, where vmax is the maximum speed of the considered DM population
Using the reflected DM population, a CRESST-III detector with a higher exposure can probe parameter space that is inaccessible with standard halo DM

Summary

INTRODUCTION

Despite convincing astrophysical evidence for the existence of dark matter (DM) in the Universe, the numerous direct-detection experiments set out to observe DM on Earth have not yet succeeded, severely constraining the classic weakly interacting massive particle (WIMP) paradigm [1,2,3]. If a light DM particle scatters off a hot nucleus inside the Sun, it will gain energy, and can exit the Sun with a speed far exceeding its incoming speed The velocity after this reflection is no longer limited by the galactic escape velocity. Since the DM velocity deep inside the Sun is dominated by the solar escape velocity, the initial distribution of the incoming halo DM has only a slight impact on the spectrum of the reflected particles These particles may be much faster than any from the halo and allow high-exposure, low-threshold direct-detection experiments to look for lighter DM than naively expected—potentially setting new constraints on sub-GeV DM, as we will show in this paper.

DARK MATTER SCATTERING IN THE SUN

Survival probability of reaching a spherical shell

Capture and reflection

Final differential scattering rate

DIRECT DETECTION

CONCLUSIONS