Coincidences of Dark Energy with Dark Matter -- Clues for a Simple Alternative?

TL;DR

This paper explores a simple extension of General Relativity involving a vector field to unify dark energy and dark matter phenomena, aiming to explain cosmic acceleration and galaxy dynamics without additional free parameters.

Contribution

It introduces the Vector-for-$oldsymbol{ extLambda}$ model, a novel kinetic vector field approach that potentially replaces dark energy and dark matter roles with a unified framework.

Findings

Model consistent with solar system and galaxy observations

Reproduces early universe inflation and late-time acceleration

Achieves a 1:3 ratio of dark matter to dark energy

Abstract

A rare coincidence of scales in standard particle physics is needed to explain why $\Lambda$ or the negative pressure of cosmological dark energy (DE) coincides with the positive pressure $P_0$ of random motion of dark matter (DM) in bright galaxies. Recently Zlosnik et al. (2007) propose to modify the Einsteinian curvature by adding a non-linear pressure from a medium flowing with a four-velocity vector field $U^\mu$. We propose to check whether a smooth extension of GR with a simple kinetic Lagrangian of $U^\mu$ can be constructed, and whether the pressure can bend space-time sufficiently to replace the roles of a $w=-1$ DE, $w=0$ Cold DM and heavy neutrinos in explaining anomalous accelerations at all scales. As a specific proof of concept we find a Vector-for-$\Lambda$ model (${\mathbf V\Lambda}$-model) and its variants. With essentially {\it no free parameters}, these appear broadly consistent with the solar system, gravitational potentials in dwarf spiral galaxies and the bullet cluster of galaxies, early universe with inflation, structure formation and BBN, and late acceleration with a 1:3 ratio of DM:DE.