Testing for a Super-Acceleration Phase of the Universe

TL;DR

The paper addresses whether the universe experienced a super-acceleration phase without assuming a specific evolution for the dark-energy density or the matter density. It introduces a model-agnostic method that fits a constant equation-of-state value to each probe, producing $\bar{w}_{\rm sn}$ from SNIa and $\bar{w}_{\rm cmb}$ from CMB, and then assesses the conditional likelihood in the $\bar{w}$–$\Omega_M$ plane to test for $\bar{w}<-1$. A detection is claimed if the upper contour crosses below $-1$ for all $\Omega_M$, leveraging complementary information from distance measures. Forecasts with SNAP-like and Planck-like data suggest robust sensitivity to past super-acceleration, even in the presence of calibration uncertainties, and the framework is adaptable to other dark-energy questions.

Abstract

We propose a method to probe the phenomenological nature of dark energy which makes no assumptions about the evolution of its energy density. We exemplify this method with a test for a super-acceleration phase of the universe i.e., a phase when the dark energy density grows as the universe expands. We show how such a phase can be detected by combining SNIa (SNAP-like) and CMB (Planck) data without making any assumptions about the evolution of the dark energy equation of state, or about the value of the matter density parameter.