Can cosmic acceleration be caused by exotic massless particles?

TL;DR

This paper proposes a fluid model with exotic massless particles that can explain cosmic acceleration without free parameters, matching observational data and offering a novel approach to dark energy.

Contribution

It introduces a new dark energy model based on exotic massless particles with a dynamical gravitational mass density, extending the Galilei algebra and satisfying Einstein's principle.

Findings

The model predicts a transition from deceleration to acceleration in cosmic expansion.

Predicted Hubble parameter and deceleration parameter align with observational data.

The model shows no stationary change in Newton's gravitational potential.

Abstract

To describe dark energy we introduce a fluid model with no free parameter on the microscopic level. The constituents of this fluid are massless particles which are a dynamical realisation of the unextended $D=(3+1)$ Galilei algebra. These particles are exotic as they live in an enlarged phase space. Their only interaction is with gravity. A minimal coupling to the gravitational field, satisfying Einstein's equivalence principle, leads to a dynamically active gravitational mass density of either sign. A two-component model containing matter (baryonic and dark) and dark energy leads, through the cosmological principle, to Friedmann-like equations. Their solutions show a deceleration phase for the early universe and an acceleration phase for the late universe. We predict the Hubble parameter $H(z)/H_0$ and the deceleration parameter $q(z)$ and compare them with available experimental data. We also discuss a reduced model (one component dark sector) and the inclusion of radiation. Our model shows no stationary modification of Newton's gravitational potential.