CCDM Model with Spatial Curvature and The Breaking of "Dark Degeneracy"

TL;DR

This paper investigates how including spatial curvature in CCDM models can break the dark degeneracy with Lambda-CDM, showing potential observational distinctions at the background level.

Contribution

It demonstrates that CCDM models with spatial curvature and specific creation rates can be distinguished from Lambda-CDM, challenging the dark degeneracy.

Findings

CCDM with spatial curvature can differ from Lambda-CDM at background level.

Current CMB data do not strongly favor either model.

The form of the CDM creation rate influences model distinguishability.

Abstract

Creation of Cold Dark Matter (CCDM), in the context of Einstein Field Equations, leads to a negative creation pressure, which can be used to explain the accelerated expansion of the Universe. Recently, it has been shown that the dynamics of expansion of such models can not be distinguished from the concordance $\Lambda$CDM model, even at higher orders in the evolution of density perturbations, leading at the so called "dark degeneracy". However, depending on the form of the CDM creation rate, the inclusion of spatial curvature leads to a different behavior of CCDM when compared to $\Lambda$CDM, even at background level. With a simple form for the creation rate, namely, $\Gamma\propto\frac{1}{H}$, we show that this model can be distinguished from $\Lambda$CDM, provided the Universe has some amount of spatial curvature. Observationally, however, the current limits on spatial flatness from CMB indicate that neither of the models are significantly favored against the other by current data, at least in the background level.