X-Ray Lines From eXciting Atomic Dark Matter
Jia Lu (NYU)

We consider the possibility that atomic DM might produce mono-energetic photon lines from the Galactic Center or other regions of high DM density, detectable in indirect detection experiments. Such a flux is generated along the lines of XDM, when dark hydrogen atoms are excited to higher energy levels in collisions and subsequently de-excite to the ground state, or alternatively when free dark electrons and dark protons recombine to form dark hydrogen atoms. The latter process is expected to be especially relevant in scenarios where interactions in the dark sector freeze out before dark recombination is complete, so that a relic density of free dark protons and dark electrons still exists today. Our goal is to compute the dark hydrogen excitation and de-excitation rates in astrophysical environments and to predict the observable photon flux at Earth from the various de-excitation lines. While our formulas will be largely independent of the masses and coupling strengths of the dark sector particles, our phenomenological analysis will focus on dark hydrogen atoms with electroweak scale masses and with binding energy of order keV, so that de-excitation lines lie in the X-ray band and are observable by satellite experiments like Chandra, Suzaku and XMM-Newton.