Abstract
We demonstrate that dark matter heating of gas clouds, hundreds of parsecs from the MilkyWay Galactic Center, provides a powerful new test of dark matter interactions. To illustrate, we set a new bound on nucleon scattering for 10-100MeV mass dark matter. We also constrain millicharged dark matter models, including those proposed to match the recent EDGES 21cm absorption anomaly. For Galactic Center gas clouds, the Galactic fields' magnetic deflection of electromagnetically charged dark matter is mitigated, because the magnetic fields around the Galactic Center are poloidal, as opposed to being aligned parallel to the MilkyWay disk. We discuss prospects for detecting dark matter using a population of Galactic Center gas clouds warmed by dark matter.
Highlights
We demonstrate that dark matter heating of gas clouds, hundreds of parsecs from the Milky Way Galactic Center, provides a powerful new test of dark matter interactions
Above-ground searches are required to find dark matter that interacts so strongly that it repeatedly scatters with nuclei and electrons during its passage through Earth’s atmosphere and crust. This is because if dark matter is moving too slowly after scattering with an overburden of atmosphere and crust, it will not deposit enough kinetic energy in underground detectors to be identified, especially in the case of sub-GeV mass dark matter, which begins its voyage with less initial kinetic energy. (For the case of very heavy dark matter, which can scatter many times with the Earth and still trigger detectors deep underground, see Ref. [8].) As a consequence, there are a number of astrophysical [9,10,11,12] and above-ground searches [13,14,15,16,17,18,19,20,21,22,23,24,25,26,27] that have the best sensitivity to dark matter with relatively strong interactions
Galactic Center gas clouds and dark matter.—Dark matter with mass mx transiting the Milky Way Galactic halo with velocity vx has a temperature, Tx ∼ mxv2x ≃ 104 KMmexV1v0x−32; which often exceeds the temperature of neutral hydrogen gas clouds, which cool to temperatures as low as ten Kelvin. (Throughout this document we take kB 1⁄4 ħ 1⁄4 c 1⁄4 1.) Atomic gas clouds with temperatures in the range 10–103 K cool via collisional excitation and subsequent de-excitation of atomic fine structure transitions, where at low temperatures the fine structure transitions of oxygen, carbon, and iron account for most of the cooling [28]
Summary
We demonstrate that dark matter heating of gas clouds, hundreds of parsecs from the Milky Way Galactic Center, provides a powerful new test of dark matter interactions. Above-ground searches are required to find dark matter that interacts so strongly that it repeatedly scatters with nuclei and electrons during its passage through Earth’s atmosphere and crust. This article demonstrates that dark matter heating of gas clouds, located hundreds of parsecs from the Milky Way. Galactic Center, can be used as a potent new method to seek out dark matter’s coupling to known particles. We discuss neutral gas cloud cooling, some recent observations of cold gas clouds hundreds of parsecs from the center of the Milky Way, and we use these to bound dark matter-nucleon interactions along with millicharged dark matter. Galactic Center gas clouds and dark matter.—Dark matter with mass mx transiting the Milky Way Galactic halo with velocity vx has a temperature (throughout we use the convention ħ 1⁄4 kB 1⁄4 c 1⁄4 1), Tx ∼ mxv2x ≃ 104 KMmexV1v0x−32; which often exceeds the temperature of neutral hydrogen gas clouds, which cool to temperatures as low as ten Kelvin. (Throughout this document we take kB 1⁄4 ħ 1⁄4 c 1⁄4 1.) Atomic gas clouds with temperatures in the range 10–103 K cool via collisional excitation and subsequent de-excitation of atomic fine structure transitions, where at low temperatures the fine structure transitions of oxygen, carbon, and iron account for most of the cooling [28]
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