Imprints of decaying dark matter on cosmic voids

The Standard Cosmological Model assumes that more than 85\% of matter is in the form of collisionless and pressureless dark matter. Unstable decaying dark matter has been proposed in the literature as an extension to the standard cold dark matter model. In this paper we investigate a scenario when dark matter decays and the resultant particle moves with respect to the dark matter. A covariant hydrodynamical model is developed in which the decay is modeled by the transfer of energy-momentum between two dark dust fluid components. We parameterise the model in terms of the decay rate $\Gamma$ and injection velocity $v_i$ of the resultant dark matter particles. We apply the framework to study the evolution of cosmic voids which are environments with low content of baryonic matter. Thus, unlike baryon-rich environments, voids provide an opportunity to measure dark matter signals that are less contaminated by complex baryonic processes. We find that the growth of S-type voids is modified by the dark matter decay, leading to imprints at the present day. This paper serves as a proof-of-concept that cosmic voids can be used to study dark mater physics. We argue that future cosmological observations of voids should focus on signs of reported features to either confirm or rule out the decaying dark matter scenario. Lack of presence of reported features could put constraints of the decay of dark matter in terms of $\Gamma > H_0^{-1}$ and $v_i<10$ km/s.