Numerical solutions to the cosmological 3-fluid problem

TL;DR

This paper investigates numerical solutions in scalar field cosmology with multiple fluids, revealing broader conditions for acceleration, effects of matter inclusion, and implications for universe expansion and structure formation.

Contribution

It extends previous studies by analyzing the 3-fluid cosmological model with exponential potential, highlighting conditions for acceleration and constraints from Big Bang Nucleosynthesis.

Findings

Broader parameter range for transient acceleration.

Inclusion of matter smooths and shifts acceleration curves.

Excess matter prevents transient acceleration, leading to eternal deceleration.

Abstract

We show that, for the scalar field cosmology with exponential potential, the set of values of the coupling parameter for which the solutions undergo a transient period of acceleration is much larger than the set discussed in the literature. The gradual inclusion of ordinary and dark matters results in an everywhere, but near the origin, smoother and right shifted (along the time axis) acceleration curve. For the 3-fluid problem, the energy density need not exhibit a plateau during the acceleration period. Much excess in the dark matter and/or ordinary matter energy densities would lead the universe to undergo an eternal deceleration expansion. For the 3-fluid problem with a single exponential potential we conclude that the Big Bang Nucleosynthesis constraint is not fulfilled if the universe is to undergo a transient period of acceleration. The 3-fluid model remains a good approximation for the description of large scale structures.