Proposal for the origin of the cosmological constant

TL;DR

This paper proposes that a vector field in a simple vector-tensor theory can naturally produce a cosmological constant-like effect, acting as dark energy with a constant energy density and pressure in an isotropic universe.

Contribution

It demonstrates that a vector field in a vector-tensor theory can serve as a source of dark energy, providing a classical origin for the cosmological constant.

Findings

The energy density of the vector field is constant over time.

The pressure of the vector field equals the negative of its energy density.

The theory's PPN parameters match those of general relativity.

Abstract

We work in the framework of a simple vector-tensor theory. The parametrized post-Newtonian approximation of this theory is identical to that of general relativity. Our attention is focused on cosmology. In an homogeneous isotropic universe, it is proved that the energy density, $\rho_{A}$, of the vector field $A$, and its pressure, $p_{A}$, do not depend on time, and also that the equation of state is $\rho_{A} = -p_{A}$. This means that, in the theory under consideration, there is a cosmological constant, which is not vacuum energy, but the dark energy of the cosmic vector field $A$, whose evolution is classical.