Interpreting Hubble tension with a cascade decaying dark matter sector

Hubble tension can be alleviated by altering either early- or late-time $Λ$CDM. So far, extensive studies have shown that only early dark energy or ad hoc combinations of those two-fold effects can reduce the tension to $3σ$ level or lower. In this work, we improve the latter solution by considering a cascade decaying dark matter sector, where a parent particle produces relativistic dark matter in the early Universe and the dark matter subsequently decays to neutrinos in the late-time Universe. We parametrize this model with four model parameters, carry out a Markov Chain Monte Carlo fit to Planck 2018+BAO+Pantheon data sets, and compare it to Big Bang Nucleosynthesis limits, neutrino flux bounds, Planck data about matter power spectrum, and structure formation constraint. Within parameter regions reducing the Hubble tension to $3.2σ$ and compatible with the existing constraints, the main phenomenological features include a larger $S_{8}\sim 0.84$, smaller $n_{s}\sim 0.95$ and larger matter power spectrum relative to the $Λ$CDM, which are left for future tests.