Can modified gravity models reconcile the tension between CMB anisotropy and lensing maps in Planck-like observations?

TL;DR

This study investigates whether modified gravity models can resolve the tension between Planck CMB anisotropy and lensing measurements by analyzing simulated spectra within the effective field theory framework.

Contribution

It demonstrates that certain modified gravity models can mimic the lensing amplitude but lead to excessive matter growth, conflicting with other observational data.

Findings

Enhanced effective Newton constant can replicate the $A_L$ parameter effects.

Such models increase matter perturbations, resulting in high $\sigma_8$ values.

High matter fluctuation amplitudes conflict with weak lensing observations.

Abstract

Planck-2015 data seem to favour a large value of the lensing amplitude parameter, $A_{\rm L}=1.22\pm0.10$, in CMB spectra. This result is in $2\sigma$ tension with the lensing reconstruction result, $A_{\rm L}^{\phi\phi}=0.95\pm0.04$. In this paper, we simulate several CMB anisotropy and CMB lensing spectra based on Planck-2015 best-fit cosmological parameter values and Planck blue book beam and noise specifications. We analyse several modified gravity models within the effective field theory framework against these simulations and find that models whose effective Newton constant is enhanced can modulate the CMB anisotropy spectra in a way similar to that of the $A_{\rm L}$ parameter. However, in order to lens the CMB anisotropies sufficiently, like in the Planck-2015 results, the growth of matter perturbations is substantially enhanced and gives a high $\sigma_8$ value. This in turn proves to be problematic when combining these data to other probes, like weak lensing from CFHTLenS, that favour a smaller amplitude of matter fluctuations.