# Dark Matter in the Sun

The minimum DM mass a detector can probe is given by

$$m_{\rm DM}^{\rm min} = \frac{m_T}{\sqrt{\frac{2m_T v_{\rm max}^2}{E_{\rm thr}}}-1}$$,

where $$m_T$$ is the targets’ mass, $$v_{\rm max}$$ is the maximum velocity of DM in the galactic halo, given by the galactic escape velocity plus the Earth’s relative motion in the galaxy, and $$E_{\rm thr}$$ is the experiment’s recoil threshold. To probe lighter DM one has to decrease the target mass or the recoil threshold. To increase the halo’s cutoff speed is of course not an option without further assumptions, but there is a second DM population in the solar system that can be much faster than halo DM particles.

A DM particle that falls into the gravitational well of the Sun might scatter on one of the hot solar nuclei, and get accelerated, as illustrated on the side. Provided that the particle can escape the Sun, we call it reflected. For sub-GeV DM, solar reflection can provide a flux of DM particles in the solar system, which is not bound by the galactic escape velocity. Given a low-threshold experiment of sufficient exposure, this effect can be used to extend DM searches to masses below the above mentioned minimum.

### Single scattering solar reflection (2017)

In collaboration with Chris Kouvaris and Niklas Grønlund Nielsen.

In our first paper on this topic, we studied the case, where the reflected DM scatters only one single time on a nucleus. For this purpose, we extended the existing theory of DM capture in the Sun to account for the Sun’s opacity and temperature. All these results are therefore based on analytic methods.

### Multiple scatterings (2021)

In my first single-author paper, I presented a comprehensive study of solar reflection via single and multiple collisions on solar nuclei and electrons. For this purpose, I developed the Monte Carlo simulation code DaMaSCUS-SUN. Not only can existing direct detection constraints on light DM be extended to lower masses (down to keV scales), I also identify and qualify an annual modulation signature of solar reflection based on the solar reflection flux’s anisotropies.

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