LATE ACCELERATED EXPANSION OF THE UNIVERSE IN DIFFUSIVE SCENARIOS

We present a diffusion model in a cosmological framework to describe the accelerated expansion of the Universe at late times. We first introduce a scalar field in Einstein's field equations to account for the effect of diffusion as the driver of today's expansion. We also study a second option for the diffusion source: a perfect fluid with a barotropic equation of state. We establish the equations that relate the fluid evolution with the cosmic budget and find analytical solutions of the field equations with different diffusion coeffcients: constant, redshift-dependent, and σ proportional to the Hubble parameter. Our main finding is that diffusive processes in the Universe are viable scenarios to effectively describe the expansion dynamics once the model's free parameters are gauged. The choice of the diffusion coeffcient and the equation of state of the cosmic fluid determines the solutions of the density fractions and the transition to an accelerated expansion of the Universe at present.