Testing backreaction effects with type Ia supernova data and observational Hubble parameter data

Abstract

The backreaction term Q D and the averaged spatial Ricci scalar R D in the spatially averaged inhomogeneous Universe can be combined into effective perfect fluid energy density ϱ eff D and pressure p eff D that can be regarded as new effective sources for the backreaction effects. In order to model the realistic evolution of backreaction, we adopt the Chevallier-Polarski-Linder (CPL) parameterizations of the equation of state (EoS) of the effective perfect fluid. To deal with observations in the backreaction context, in this paper, we employ two metrics to describe the late time Universe, one of them is the standard Friedmann-Lemaître-Robertson-Walker(FLRW) metric, and the other is a template metric with an evolving curvature parameter introduced by Larena et. al. in their previous article. For comparison, we fit our CPL backreaction model as well as the well-known scaling backreaction model using type Ia supernova (SN Ia) data and observational Hubble parameter data (OHD) with these two metrics, and find out that parameter tensions between two different data sets are extremely larger in the template metric context for the scaling backreaction model, and moderately larger in the template metric context for the CPL backreaction model, therefore we conclude that the prescription of the geometrical instantaneous spatially-constant curvature κ D needs to be modified.