An effective theory of accelerated expansion

TL;DR

This paper develops an effective, model-independent framework for describing cosmic acceleration phenomena like inflation and dark energy, identifying key parameters that can be constrained through observations of the expansion rate.

Contribution

It introduces a leading-order effective theory with five parameters for cosmic acceleration, clarifying their physical interpretation and observational constraints.

Findings

Five independent parameters at leading order describe cosmic acceleration.

One parameter can be constrained by general relativity tests.

Remaining four parameters are determined by measuring H(z).

Abstract

We work out an effective theory of accelerated expansion to describe general phenomena of inflation and acceleration (dark energy) in the Universe. Our aim is to determine from theoretical grounds, in a physically-motivated and model independent way, which and how many (free) parameters are needed to broadly capture the physics of a theory describing cosmic acceleration. Our goal is to make as much as possible transparent the physical interpretation of the parameters describing the expansion. We show that, at leading order, there are five independent parameters, of which one can be constrained via general relativity tests. The other four parameters need to be determined by observing and measuring the cosmic expansion rate only, H(z). Therefore we suggest that future cosmology surveys focus on obtaining an accurate as possible measurement of $H(z)$ to constrain the nature of accelerated expansion (dark energy and/or inflation).