Cosmic Microwave Weak lensing data as a test for the dark universe

TL;DR

This paper analyzes WMAP and ACBAR data to detect gravitational lensing effects in the cosmic microwave background, finding a potential excess lensing signal that could challenge standard cosmological models.

Contribution

It introduces a new parameter A_L to quantify lensing amplitude and provides the first indication of a lensing signal larger than expected from current data.

Findings

2.5 sigma indication of excess lensing

A_L=3.1_{-1.5}^{+1.8} at 95% confidence level

Result stable under various foreground assumptions

Abstract

Combined analyses of WMAP 3-year and ACBAR Cosmic Microwave Anisotropies angular power spectra have presented evidence for gravitational lensing >3 sigma level. This signal could provide a relevant test for cosmology. After evaluating and confirming the statistical significance of the detection in light of the new WMAP 5-year data, we constrain a new parameter A_L that scales the lensing potential such that A_L=0 corresponds to unlensed while A_L=1 is the expected lensed result. We find from WMAP5+ACBAR a 2.5 sigma indication for a lensing contribution larger than expected, with A_L=3.1_{-1.5}^{+1.8} at 95% c.l.. The result is stable under the assumption of different templates for an additional Sunyaev-Zel'dovich foreground component or the inclusion of an extra background of cosmic strings. We find negligible correlation with other cosmological parameters as, for example, the energy density in massive neutrinos. While unknown systematics may be present, dark energy or modified gravity models could be responsible for the over-smoothness of the power spectrum. Near future data, most notably from the Planck satellite mission, will scrutinize this interesting possibility.