I will introduce a particle model in which the dark matter particle is an atom, a bound state of two fermions in the hidden sector. The binding force of the dark matter atom is a new gauge boson. A kinetic mixing term between the new gauge boson and the photon can mediate dark matter direct detection in underground labs. The recently observed 3.5 keV X-ray excess can be explained by the “21 cm” line of the atomic dark matter. As a composite object, atomic dark matter is able to generate a rather large self-interacting cross section with ease. Such a self-interaction is a viable solution to the small scale puzzles, the discrepancy between astrophysical observations at the galaxy-size scales and the cold dark matter N-body simulations.

                                                Host: Prof. Wei Wang