ISW effect as probe of features in the expansion history of the Universe

TL;DR

This study investigates how modifications in the Universe's expansion history affect the CMB power spectrum, using a new computational tool and MCMC analysis, revealing that a decaying dark energy model slightly outperforms the standard LCDM model.

Contribution

Introduces CMBAns, a new line of sight CMB code, to analyze the impact of different expansion histories on the CMB power spectrum and compares models using MCMC analysis.

Findings

Decaying dark energy model fits CMB data marginally better than LCDM.

Expansion history variations are consistent with standard LCDM within uncertainties.

BAO and SN Ia data also mildly favor the decaying dark energy model.

Abstract

In this paper, using and implementing a new line of sight CMB code, called CMBAns [1], that allows us to modify H(z) for any given feature at any redshift we study the effect of changes in the expansion history of the Universe on the CMB power spectrum. Motivated by the detailed analytical calculations of the effects of the changes in H(z) on ISW plateau and CMB low multipoles, we study two phenomenological parametric form of the expansion history using WMAP data and through MCMC analysis. Our MCMC analysis shows that the standard LCDM cosmological model is consistent with the CMB data allowing the expansion history of the Universe vary around this model at different redshifts. However, our analysis also shows that a decaying dark energy model proposed in [2] has in fact a marginally better fit than the standard cosmological constant model to CMB data. Concordance of our studies here with the previous analysis showing that Baryon Acoustic Oscillation (BAO) and supernovae data (SN Ia) also prefer mildly this decaying dark energy model to LCDM, makes this finding interesting and worth further investigation.