Probing primordial features with the primary CMB

TL;DR

This paper proposes a method to isolate primordial CMB features by removing secondary effects like the ISW signal, enhancing the ability to test early universe physics and better constrain models explaining large-scale anomalies.

Contribution

The study introduces a technique to reconstruct primary CMB anisotropies by subtracting the ISW effect, improving constraints on primordial features and addressing large-scale anomalies.

Findings

Significant improvement in constraints on feature parameters, up to 16% for quadrupole suppression.

Enhanced ability to distinguish early- from late-time physics effects.

Potential to clarify the origins of large-scale CMB anomalies.

Abstract

CMB photons travel from the last scattering surface, when the primary CMB has been generated, along the surface of the light cone to us. During their travel, they are affected by many secondary effects such as the integrated Sachs-Wolfe effect and CMB lensing. These CMB secondary effects modify the CMB primary power spectrum adding degeneracies and decreasing the sensibility to primordial parameters. The possibility to reconstruct the primary CMB anisotropies will allow us to have a more direct observable to test the physics of the early universe. We propose to study the imprint of features in the primordial power spectrum with the primary CMB after the subtraction of the reconstructed ISW signal from the observed CMB temperature angular power spectrum. We consider the application to features models able to fit two of the large scales anomalies observed in the CMB temperature angular power spectrum: the deficit of power at $\ell \sim 2$ and at $\ell \sim 22$. This method allows to improve significantly the constraints on the features parameters up to $16\%$ for models predicting a suppression of power of the quadrupole and up to $27\%$ for models with features at $\ell \sim 22$, assuming instrumental sensitivity similar to the $Planck$ satellite (depending on the goodness of the ISW reconstruction). Furthermore, it gives the opportunity to understand if these anomalies are attributed to early- or late-time physics.