Self-interacting dark matter and cosmology of a light scalar mediator

Understand

We consider a fermionic dark matter candidate interacting via a scalar mediator coupled with the Standard Model through a Higgs portal.

• We consider general setting including both scalar and pseudoscalar interactions between the scalar and fermion, and illustrate the relevant features for dark matter abundance, direct search limits and collider constraints.
• The case where dark matter has a self-interaction strength $\left\langle \sigma_V \right\rangle/m_\psi \sim 0.1-1 \,\mathrm{cm}^2/\mathrm{g}$ is strongly constrained, in particular by the Big Bang Nucleosynthesis.
• We show that these constraints can be alleviated by introducing a new light sterile neutrino $N$.