Unified dark energy and dark matter from a scalar field different from quintessence

TL;DR

This paper proposes a novel scalar field model that unifies dark matter and dark energy, differing from quintessence, and demonstrates its observational viability using cosmological data.

Contribution

It introduces a non-Lagrangian scalar field with unique properties for unification of dark components, distinct from existing models like quintessence.

Findings

Scalar field has an equation of state between -1 and 0.

Model fits cosmological data for small exponential potential parameter.

Zero sound speed in the rest frame supports structure formation compatibility.

Abstract

We explore unification of dark matter and dark energy in a theory containing a scalar field of non-Lagrangian type, obtained by direct insertion of a kinetic term into the energy-momentum tensor. This scalar is different from quintessence, having an equation of state between -1 and 0 and a zero sound speed in its rest frame. We solve the equations of motion for an exponential potential via a rewriting as an autonomous system, and demonstrate the observational viability of the scenario, for sufficiently small exponential potential parameter \lambda, by comparison to a compilation of kinematical cosmological data.