A novel approach to cosmological non-linearities as an effective fluid

A novel approach to cosmological non-linearities as an effective fluid
Leonardo Giani, Rodrigo Von Marttens, Ryan Camilleri
arXiv:2410.15295v2 Announce Type: replace
Abstract: We propose a two parameters extension of the flat $Lambda$CDM model to capture the impact of matter inhomogeneities on our cosmological inference. Non virialized but non-linearly evolving overdense and underdense regions, whose abundance is quantified using the Press-Schechter formalism, are collectively described by two effective perfect fluids $rho_{rm{c}},rho_{rm{v}}$ with non vanishing equation of state parameters $w_{rm{c,v}}neq 0$. These fluids are coupled to the pressureless dust, akin to an interacting DM-DE scenario. The resulting phenomenology is very rich, and could potentially address a number of inconsistencies of the standard model, including a simultaneous resolution of the Hubble and $sigma_8$ tensions. To assess the viability of the model, we set initial conditions compatible to the Planck 2018 best fit $Lambda$CDM cosmology and fit its additional parameters using SN~Ia observations from DESY5, BAO distances from DESI DR2 and a sample of uncorrelated $fsigma_8$ measurements. Our findings show that backreaction effects from the cosmic web could restore the concordance between early and late Universe cosmological probes.arXiv:2410.15295v2 Announce Type: replace
Abstract: We propose a two parameters extension of the flat $Lambda$CDM model to capture the impact of matter inhomogeneities on our cosmological inference. Non virialized but non-linearly evolving overdense and underdense regions, whose abundance is quantified using the Press-Schechter formalism, are collectively described by two effective perfect fluids $rho_{rm{c}},rho_{rm{v}}$ with non vanishing equation of state parameters $w_{rm{c,v}}neq 0$. These fluids are coupled to the pressureless dust, akin to an interacting DM-DE scenario. The resulting phenomenology is very rich, and could potentially address a number of inconsistencies of the standard model, including a simultaneous resolution of the Hubble and $sigma_8$ tensions. To assess the viability of the model, we set initial conditions compatible to the Planck 2018 best fit $Lambda$CDM cosmology and fit its additional parameters using SN~Ia observations from DESY5, BAO distances from DESI DR2 and a sample of uncorrelated $fsigma_8$ measurements. Our findings show that backreaction effects from the cosmic web could restore the concordance between early and late Universe cosmological probes.