Title：Constraining cosmic inflation with CMB B-modes from ground and space

Speaker：Tommaso Ghigna

Abstract:CMB polarimetry has undergone a remarkable transformation over the last two decades. What began as a field driven by small, ground-based observatories managed by a handful of scientists has evolved into a collection of large-scale international projects. This shift has been essential in advancing our ability to probe the cosmic microwave background (CMB) with increasing precision. Through this progression, researchers have been able to test and refine various technologies, observational techniques, and instrument configurations. Additionally, different observatory locations have been evaluated to determine the most suitable environments for detecting the faint polarization signals of the CMB. A key objective of these efforts has been to identify the optimal combination of methods to constrain polarized B-modes, a critical signature that could provide strong evidence for cosmic inflation.

While ground-based observatories have been instrumental in these advancements, they face fundamental limitations. Factors such as atmospheric opacity, restricted observing frequencies, and the challenge of accessing the largest angular scales make ground-based observations insufficient for fully characterizing the CMB’s primordial B-modes. Consequently, there is a growing interest within the scientific community in a space-based multi-frequency, all-sky survey. A space mission would allow for more comprehensive measurements, free from atmospheric interference, and could provide unprecedented constraints on inflationary physics.

However, space-based missions impose significantly more stringent requirements on instrument design and fabrication. In particular, the uniformity and performance of detector arrays must meet high standards, as space-based instruments cannot be easily adjusted or repaired once deployed.

In this talk I will give a broad overview of the status of CMB science, and touch on the open problems and strategies for future observations. I will introduce the LiteBIRD space mission (led by the Japanese Space Agency - JAXA) and its status. I will conclude with an overview of the main topics I am involved in, related not only to LiteBIRD, but CMB observations more broadly.

Bio: Tommaso Ghigna - Assistant Professor at QUP (International Center for Quantum-field Measurement Systems for Studies of the Universe and Particles), Tsukuba, Japan.

I am an astrophysicist by training with a strong interest in instrumentation. I have been interested in cosmology and the CMB since I was an undergraduate student in Milan, Italy. In order to follow my passion, I moved for my doctorate to Oxford, UK where I was also involved in the development of the first prototype of the SKA Band 5 receiver. After a few years I moved to Kavli IPMU in Japan, first as an exchange student and then as a postdoctoral researcher. Here my main project became the LiteBIRD space mission. In 2022 I moved to QUP to focus on the TES detector development for the LiteBIRD telescope. In 2023 I became an assistant professor (and deputy Principal Investigator) at QUP.

Time: 15:30-16:30, 25/February, Tuesday 

Venue: Room 506 (Large seminar room), Department of Astronomy