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One of the key predictions of the WIMP paradigm for Dark Matter (DM) is thatDM particles can annihilate into charged particles. These annihilations willproceed in e.g. Galactic subhalos such as dwarf Galaxies or, as recentlypointed out, high velocity clouds such as the "Smith Cloud". In this note, wefocus on the radio emission associated with DM annihilations into electrons andpositrons occurring in the Smith Cloud. The phenomenology of this emission isdiscussed in quite some detail. We argue that the uncertainties in thepropagation can be captured by the typical diffusion-loss length parameter(Syrovatskii variable) but that the angle-integrated radio fluxes areindependent of the propagation. We conclude that if the Smith Cloud is indeeddominated by DM, radio signals from DM annihilation stand out amongst othermessengers. Furthermore, low frequencies such as the ones observed by e.g. theLow Frequency Array (LOFAR) and the next-generation Square Kilometre Array(SKA) are optimal for searches for DM in the Smith Cloud. As a practicalapplication, we set conservative constraints on dark matter annihilation crosssection using data of continuum radio emission from the Galaxy at 22 MHz and at1.4 GHz. Stronger constraints could be reached by background subtraction,exploiting the profile and frequency dependence of the putative DM signal. Weset stronger but tentative limits using the median noise in brightnesstemperature from the Green Bank Telescope and the LOFAR sensitivities.

Synchrotron Emission from Dark Matter in Galactic Subhalos. A Look into the Smith Cloud