Scheme: University Research Fellowship
Organisation: University of Manchester
Dates: Jan 2015-Dec 2019
Summary: Cosmology is now a precise scientific discipline, with detailed theoretical models that fit a wealth of very accurate measurements. Of the many cosmological data sets, the cosmic microwave background (CMB) temperature and polarization anisotropies provide the most stringent and robust constraints to theoretical models, allowing us to determine the key parameters of our Universe and address fundamental questions about inflation and early-universe physics. But the CMB holds another, complementary and independent piece of invaluable information: its frequency spectrum. Departures of the CMB frequency spectrum from a blackbody -- commonly referred to as spectral distortions -- encode information about the thermal history of the early Universe (from when it was a few month old until today). Since the measurements with COBE/FIRAS, the average CMB spectrum is known to be extremely close to a perfect blackbody, with possible distortions limited to one part in ten thousand. This impressive measurement was awarded the Nobelprize in Physics 2006, and already rules out cosmologies with extended periods of significant energy release, disturbing the thermal equilibrium between matter and radiation in the Universe.
However, this is not the end of the story. Firstly, even within the standard cosmological paradigm, several processes (e.g., heating because of reionization and structure formation) give rise to guaranteed CMB distortion signals. Secondly, benefiting from technological advances over the past quarter-century since COBE/FIRAS, a much more precise characterization of the CMB spectrum may soon be possible. This will open an unexplored window to the early Universe, on the one hand allowing us to directly probe standard processes (e.g., dissipation of primordial density fluctuations at small scales), on the other also opening up a huge discovery space for non-standard physics (e.g., decaying/annihilating particles or cosmic strings). The goal of my research is to help paving the path to this exciting new era of CMB science.