Uplifting, Depressing, and Tilting Dark Energy

TL;DR

This paper investigates dark energy models that can explain the observed acceleration patterns, finding that typical interaction models struggle to fit data unless dark energy itself crosses the phantom divide, which is physically unusual.

Contribution

It demonstrates that common interaction-based dark energy models generally fail to fit cosmological data unless dark energy crosses w=-1, highlighting the need for such crossing.

Findings

Interaction models often do not fit data well

Dark energy must cross w=-1 to match observations

Crossing w=-1 is physically unusual

Abstract

Current data in the form of baryon acoustic oscillation, supernova, and cosmic microwave background distances prefer a cosmology that accelerates more strongly than $\Lambda$CDM at $z\approx0.5-1.5$, and more weakly at $z\lesssim0.5$. We examine dark energy physics that can accommodate this, showing that interactions (decays, coupling to matter, nonminimal coupling to gravity) fairly generically tend not to give a satisfactory solution (in terms of fitting both distances and growth) even if they enable the effective dark energy equation of state to cross $w=-1$. To fit the cosmological data it appears the dark energy by itself must cross $w=-1$, a highly unusual physical behavior.