Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

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

Erminia Calabrese, Anze Slosar, Alessandro Melchiorri, George F. Smoot, Oliver Zahn

TL;DR

This paper reanalyzes the ACBAR CMB power spectrum in light of a claimed lensing signal, introducing an amplitude parameter $A_L$ that scales the lensing potential and constraining it with WMAP3/5 and ACBAR (plus broader data sets). Using an 8-parameter cosmology with Markov chain Monte Carlo, the authors find a persistent preference for $A_L>1$ at about 2–3σ, indicating the observed smoothing of acoustic peaks is not easily explained by unlensed models. Bayesian evidence favors the lensed interpretation, and the result appears robust to alternative foreground templates but remains sensitive to potential unknown systematics. They discuss possible explanations in terms of modified gravity or dark energy and emphasize that Planck data, especially polarization, will be crucial to confirm or refute this hint of new physics.

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.

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

TL;DR

This paper reanalyzes the ACBAR CMB power spectrum in light of a claimed lensing signal, introducing an amplitude parameter that scales the lensing potential and constraining it with WMAP3/5 and ACBAR (plus broader data sets). Using an 8-parameter cosmology with Markov chain Monte Carlo, the authors find a persistent preference for at about 2–3σ, indicating the observed smoothing of acoustic peaks is not easily explained by unlensed models. Bayesian evidence favors the lensed interpretation, and the result appears robust to alternative foreground templates but remains sensitive to potential unknown systematics. They discuss possible explanations in terms of modified gravity or dark energy and emphasize that Planck data, especially polarization, will be crucial to confirm or refute this hint of new physics.

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.

Paper Structure

This paper contains 8 sections, 8 equations, 3 figures, 2 tables.

Table of Contents

  1. Introduction
  2. Analysis Method
  3. Basic claim and its statistical significance
  4. Varying $A_L$
  5. Additional components
  6. Non standard models
  7. Systematics
  8. Conclusions

Figures (3)

  • Figure 1: This figure shows the effect of varying $A_L$ parameter. The curves with increasingly smoothed peak structure correspond to values of $A_L$ of $0$,$1$,$3$,$6$,$9$.
  • Figure 2: This figure shows the ACBAR data with $C_\ell$ spectrum predictions suitably multiplied to show the structure of the peaks more clearly.
  • Figure 3: Marginalized $1$-D likelihood disribution for $A_L$ for different datasets considered: WMAP3-alone (solid bold), WMAP3+ACBAR (dotted), WMAP3+"everything" (dotted bold), WMAP3+ACBAR+strings (solid), WMAP3+ACBAR+SZ1 (dashed), WMAP3+ACBAR+SZ2 (dotted-dash).