A Cosmological Lever Arm for Fundamental Physics

Key open questions in the boundary of cosmology and fundamental physics can be addressed by studies of the distribution of matter as a function of scale and time (or redshift). While the traditional approach has been to use large galaxy catalogues, during the last decade I have pioneered the use of an alternative probe: 3D correlations in the Lyman-α (Lyα) forest, absorption features in the spectra of high-redshift quasars caused by intervening neutral hydrogen. The Lyα forest provides a unique window to study the distribution of matter at earlier times and on smaller scales than those accessible with galaxy catalogues.I lead the Lyα analysis of the Dark Energy Spectroscopic Instrument (DESI) survey, and with ERC support I will be able to develop and apply new techniques to dramatically enhance its expected outcome. On one hand, COSMO-LYA we will use the correlations on large (> 30 Mpc) scales to obtain a 0.5% measurement of the expansion rate of the Universe at z > 2, four times better than the state-of-the-art. On the other hand, we will carry out the first coherent analysis of 1D and 3D correlations to provide a 1% measurement of the amplitude of density fluctuations on small (~1 Mpc) scales, unreachable by other probes. In combination with public CMB results, sensitive to the distribution of matter at early times and on the largest scales, we will be able to construct a cosmological lever arm covering 4 orders of magnitude in scale. This will enable my team to: i) increase by at least a factor of 2 the constraints on the sum of the neutrino masses, potentially leading to the first measurement of the absolute neutrino masses; ii) increase by at least a factor of 3 our constraints on the shape of the primordial power spectrum of density fluctuations, an important step towards confirming or falsifying a large number of inflationary models. These results will have interdisciplinary impact, with wide reaching consequences into particle and fundamental physics.