Abstract
Abstract
In this paper, we construct a viable model for a GeV scale self-interacting dark
matter (DM), where the DM was thermally produced in the early universe. Here, a new vector-like
fermion with a dark charge under the U(1)_D gauge symmetry serves as a
secluded WIMP DM and it can dominantly annihilate into the light dark gauge boson and singlet
scalar through the dark gauge interaction. Also, the self-interaction of DM is induced by the
light dark gauge boson via the same gauge interaction. In addition to these particles, we further
introduce two Weyl fermions and a doublet scalar, by which the dark gauge boson produced from
s-wave DM annihilations can mostly decay into active neutrinos after the dark symmetry
breaking such that the CMB bound on the DM with low masses can be eluded. In order to have a
common parameter region to explain the observed relic abundance and self-interaction of DM, we
also study this model in a non-standard cosmological evolution, where the cosmic expansion driven
by a new field species is faster than the standard radiation-dominated universe during the
freeze-out of DM. Reversely, one can also use the self-interacting nature of light thermal DM to
examine the non-standard cosmological history of the universe.