Late Time Cosmology with Viscous Self-interacting Dark Matter

Self-interacting dark matter (SIDM) is an intriguing possibility to address the small scale problems faced by the collisionless cold dark matter. The self interaction between the dark matter (DM) particles can lead to viscosity. At late times, this viscosity can become strong enough to account for the present observed cosmic acceleration, and hence mimic the dark energy. In this work, using a power law form of the average peculiar velocity gradient of the DM, we calculate the Hubble expansion rate and the deceleration parameter for small redshifts (0 ≤ z≤ 2.5 ). We then estimate the model parameters from χ² analysis and argue that the dissipational effect of viscous SIDM is small at the early times and become prominent at the late time. Later, we match our viscous SIDM model with the small redshift data and find that this model explains the data very well. Our analysis is independent of any SIDM particle Physics model.