Line of research overview

Cosmic Microwave Background

Principal Investigator: Nicoletta Krachmalnicoff

Abstract:

This line of research is dedicated to the simulation, analysis and interpretation of the Cosmic Microwave Background (CMB) signal, serving as a crucial tool for probing the early universe and its evolutionary processes. The scope of our activities covers the entirety of this scientific domain, ranging from simulations and data analysis to the extraction of cosmological information. Specifically our scientific focus lies on unraveling the physics of the early Universe – through cosmological gravitational waves (GWs) – as well as on the nature of dark matter and energy and possible modification of gravity – through CMB gravitational lensing and cross correlation with other cosmic fields.

The team involved in these studies holds direct responsibilities in both the management and scientific aspects of current and future CMB experiments, in particular: the ongoing Simons Array and Simons Observatory projects, as well the CMB-Stage IV ground based experiment and the LiteBIRD satellite, scheduled for the observation in the next decade.

Status of project and perspectives:

Current and future CMB experiments mainly focus on the measurements of the polarized signal since potential groundbreaking discoveries are hidden in the curl component of the CMB polarization field, the so-called B-modes. At large angular scales, the B-mode signal carries the imprint of primordial GWs, predicted as a manifestation of quantum gravity within the inflationary theoretical paradigm. At the opposite end, at smaller angular scales, the B-mode polarization pattern is a consequence of gravitational lensing, and can provide new insight on the structures and content of the universe. Those measurements are extremely challenging and require major efforts in the development and testing of data analysis techniques.

In this context, our line of research includes the following topics:

• B-modes and Galactic foregrounds: we develop robust data analysis tools for detecting the primordial B-mode signal. This includes activities such as: component separation, modeling Galactic polarized signals, addressing instrumental systematic effects, lensing reconstruction, de-lensing, and parameter estimation using Bayesian methods and machine learning techniques. These efforts apply to existing datasets and to simulations, preparing for future experiments. Special attention is given to optimizing scientific results through the combination of diverse datasets from multiple CMB experiments.
• Cross-correlation: we explore the cross-correlation of CMB anisotropies with tracers of large-scale structures observed through dedicated probes such as the Euclid satellite of the European Space Agency. This is crucial for measuring the efficiency of structure formation and, consequently, the expansion rate during the epoch when dark energy began influencing the cosmic expansion rate. Additionally, cross-correlation validates algorithmic approaches, such as de-lensing, which effectively suppress lensing contamination in cosmological GW studies.
• Ground segment for space mission: our activities aim to enhance understanding of the design and implementation of a ground segment for space missions. Drawing from the experience gained with Planck and managing the Euclid Ground Segment, we leverage this knowledge to explore new technologies essential for upcoming missions like LiteBird.