Self-Interacting Dark Matter With a Neutrinophilic Scalar Mediator.

We examine the phenomenology of a simplified model of fermionic dark matter coupled to a light scalar mediator carrying lepton number 2. We find that the mediator can be very light and still consistent with laboratory and cosmological bounds. This model satisfies the thermal relic condition for natural values of dimensionless coupling constants and admits a mediator in the $10 - 100 ~\text{MeV}$ mass range favored by small scale structure observations. As such, this model provides an excellent candidate for self-interacting dark matter.