Observational constraints on the free parameters of an interacting Bose–Einstein gas as a dark-energy model

Dark energy is modelled by a Bose–Einstein gas of particles with an attractive interaction. It is coupled to cold dark matter, within a flat universe, for the late-expansion description, producing variations in particle-number densities. The model’s parameters, and physical association, are: Ω G 0 , Ω m 0 , the dark-energy rest-mass energy density and the dark-matter term scaling as a mass term, respectively; Ω i 0 , the self-interaction intensity; x , the energy exchange rate. Energy conservation relates such parameters. The Hubble equation omits Ω G 0 , but also contains h , the present-day expansion rate of the flat Friedman–Lemâitre–Robertson–Walker metric, and Ω b 0 , the baryon energy density, used as a prior. This results in the four effective chosen parameters Ω b 0 , h , Ω m 0 , Ω i 0 , fit with the Hubble expansion rate H ( z ), and data from its value today, near distance, and supernovas. We derive wide 1 σ and 2 σ likelihood regions compatible with definite positive total CDM and IBEG mass terms. Additionally, the best-fit value of parameter x relieves the coincidence problem, and a second potential coincidence problem related to the choice of Ω G 0 .