2021/09/30 by Natalie B Hogg, Natalie B. Hogg, Marco Bruni
Physics and Astronomy · #Astrophysics #Baryon acoustic oscillations #Cosmic microwave background #Cosmology #Cosmology and Gravitation Theories #Coupling (piping) #Dark energy #Equation of state #Galaxies: Formation, Evolution, Phenomena #Matter power spectrum #Physics #Quantum mechanics #Scientific Research and Discoveries #Statistical physics #Theoretical physics #Vacuum energy #astro-ph.CO
paper · pdf · doi:10.1093/mnras/stac324
14 pages, 11 figures. Results and discussion updated to match version published in MNRAS. Short appendix with extra results added
openalex publication_date 2022/02/03 · arxiv created 2022/02/28 · arxiv updated 2022/03/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
In this paper, we introduce a novel class of interacting vacuum models, based on recasting the equation of state originally developed in the context of lattice kinetic theory by Shan & Chen as the coupling between the vacuum and cold dark matter (CDM). This coupling allows the vacuum to evolve and is nonlinear around a characteristic energy scale ρ_*, changing into a linear coupling with a typical power law evolution at scales much lower and much higher than ρ_*. Focusing on the simplest sub-class of models where the interaction consists only of an energy exchange and the CDM remains geodesic, we first illustrate the various possible models that can arise from the Shan--Chen coupling, with several different behaviours at both early and late times depending on the values of the model parameters selected. We then place the first observational constraints on this Shan--Chen interacting vacuum scenario, performing an MCMC analysis to find those values of the model and cosmological parameters which are favoured by observational data. We focus on models where the nonlinearity of the coupling is relevant at late times, choosing for the reference energy scale ρ_*, the critical energy density in ΛCDM. We show that the observational data we use are compatible with a wide range of models which result in different cosmologies. However, we also show that ΛCDM is preferred over all of the Shan--Chen interacting vacuum models that we study, and comment on the inability of these models to relax the H0 and σ8 tensions.