Dark Energy as a Modification of the Friedmann Equation

TL;DR

This paper proposes that dark energy might be explained by modifications to the Friedmann equation from new physics, analyzing its phenomenology, detectability, and implications for future observations.

Contribution

It introduces a specific phenomenological correction to the Friedmann equation and explores its implications for dark energy behavior and observational detectability.

Findings

Correction behaves like dark energy with variable equation-of-state

Correction parameter $eta$ must be less than or approximately 1

Future supernova experiments could constrain the correction parameter

Abstract

Dark energy could actually be the manifestation of a modification to the Friedmann equation arising from new physics (e.g., extra dimensions). Writing the correction as $(1-\Omega_M)H^\alpha /H_0^{\alpha -2}$, we explore the phenomenology and detectability of such. We show that: (i) $\alpha$ must be $\la 1$; (ii) such a correction behaves like dark energy with equation-of-state $w_{\rm eff} = -1 + {\alpha \over 2}$ in the recent past ($10^4> z\gg 1$) and $w=-1$ in the distant future and can mimic $w<-1$ without violating the weak-energy condition; (iii) $w_{\rm eff}$ changes, $dz/dw|_{z\sim 0.5} \sim {\cal O}(0.2)$, which is likely detectable; and (iv) a future supernova experiment like SNAP that can determine $w$ with precision $\sigma_w$, could determine $\alpha$ to precision $\sigma_\alpha \approx 2 \sigma_w$.