Speaker
Description
The only precise measurement of the cosmic microwave background (CMB) spectrum to date was achieved by COBE-FIRAS in the early 1990s, demonstrating that the CMB spectrum is extraordinarily close to a perfect blackbody emission. However, both standard and non-standard physical processes are expected to generate small deviations from this spectrum, known as CMB spectral distortions. These distortions provide a unique and largely unexplored probe of the thermal history of the Universe, offering complementary insights into early-Universe physics, particle interactions, and structure formation. The measurement of CMB spectral distortions has therefore become a major objective for future cosmology missions and is now recognised as one of the three key scientific goals of the ESA Voyage 2050 programme. Since 2011, several dedicated space missions have been proposed, FOSSIL being the latest one, having been submitted to the ESA M8 call. In addition, pathfinders projects such as the balloon-borne experiment BISOU (CNES Phase A) are being developed targeting the first CMB spectral distortion monopole detection. After a brief overview of the observational challenges associated with spectral distortion measurements, I will present the latest optimization and forecasting studies for the BISOU and FOSSIL) projects. For this purpose, a flexible spectro-photometric model based on key instrument design choices and subsystem parameters, and a sky emission model dedicated to CMB spectral distortions studies have been developed.