Determination of the masses of cosmological neutrinos – NuMass

We propose to use data collected by the BOSS experiment between 2009 and 2014. By the end of the survey, up to 160,000 quasar spectra should be measured, exceeding previously available data sets by over an order of magnitude. We will combine the expertise of experimentalists and theorists to address all the issues of the problem in a global perspective: we will on the one hand analyze the obtained quasar spectra to derive the flux power spectrum, and simulate, on the other hand, the distribution of matter in the Universe in the presence of massive neutrinos, through a hybrid hydrodynamical and N-body simulation that we will develop. We will run these simulations on the largest superclusters availabale in Europe, such as the TGCC in Bruyeres-le-Chatel.

We will then be able to generalize our analysis pipeline that we developped for active neutrinos, in order to derive in a latter stage similar constraints on possible sterile neutrinos and on various types of warm dark matter candidates.

The main results of this project are presented in a total of four publications led by the project consortium, and related communications:

- The one-dimensional Ly-alpha forest power spectrum from BOSS
- New approach for precise computation of Lyman-alpha forest power spectrum with hydrodynamical simulations
- Hydrodynamical Simulations of the Lyman-Alpha Forest with Massive Neutrinos
- Constraint on neutrino masses from SDSS-III/BOSS Ly-alpha forest and other cosmological probes

The quality of the BOSS DR9 quasar data and the thoroughness of the analysis led by the consortium are such that the improvement on the measurement of the 1D transmitted flux power spectrum leads to a factor 2-3 smaller error bars than those obtained from previous measurements. The developments undertaken in the course of this project can therefore be further extended to include constraints on sterile neutrinos or warm dark matter components.

The scientific production consists in the four papers listed above.

A major breakthrough in particle physics over the last decade is the confirmation that neutrinos are massive. Their mass, however, remains unknown and is the source of intense research activity. In the near future, cosmological data are expected to offer the best sensitivity to the neutrino mass, better than can be achieved with laboratory experiments. The objective of this proposal is to use the signature left in quasar spectra by the presence of neutral hydrogen in the Universe to measure, or constrain, the sum of the masses of the three neutrino flavors at the ~0.1 eV level. With such a sensitivity, we can determine the absolute mass scale of neutrinos by combining particle physics and cosmology results. To reach this goal, we formed a team of scientists working at the frontier between these two communities.

We propose to use data collected by the BOSS experiment between 2009 and 2014. By the end of the survey, up to 160,000 quasar spectra should be measured, exceeding previously available data sets by over an order of magnitude. We will combine the expertise of experimentalists and theorists to address all the issues of the problem in a global perspective: we will, on the one hand, analyze the obtained quasar spectra to derive the flux power spectrum, and simulate, on the other hand, the distribution of matter in the Universe in the presence of massive neutrinos, through a hybrid hydrodynamical and N-body simulation that we will develop.

We will then be able to generalize our analysis pipeline for active neutrinos, in order to derive similar constraints on possible sterile neutrinos and on various types of warm dark matter candidates.

Measuring the impact of massive neutrinos on structure formation in the Universe is a milestone towards an accurate and consistent “minimal cosmological model”. At the same time, this project offers a unique opportunity to answer one of the most burning questions in particle physics, and to provide some hints on new fundamental theories.