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.