ANR-DFG - Appel à projets générique 2022 - DFG

The DESI Lyman-alpha data: first analysis and contraints on neutrinos and Dark Matter – DESI-Lya

Submission summary

With the advent of new-generation optical surveys, a major step forward can be taken on fundamental questions in particle physics and cosmology, none the least being the unknown values of the neutrino masses (Mnu) and the nature of dark matter (DM). The Lyman-alpha (Ly-a) forest is a measurement of fluctuations in the absorption of light by neutral hydrogen at redshifts from 2 to 5. As a unique probe of the related small-scale, high-redshift matter fluctuations, it is a precious tool to address these questions. The Dark Energy Spectroscopic Instrument (DESI) is the world-leading wide-field cosmological spectroscopic survey, which started its main survey in 2021. It is now providing Ly-a forest data with unprecedented statistics and quality. New measurements of Mnu and DM properties will therefore be possible in the near future, provided theoretical predictions for the Ly-a forest are computed with a precision adapted to these data.

Benefitting from the already existing synergy between the Saclay and Aachen groups, the DESI-Lya project will be two-folds. On the one hand, it will focus on the study of small-scale DESI Ly-a data. This will be done first by applying existing methods to measure the 1D power spectrum of the Ly-a absorption flux. This measurement is very sensitive to instrumental properties and related systematics, and therefore requires work to apply on the new DESI instrument. In a second step, a novel approach to measure the small-scale, 3D Ly-a power spectrum will be implemented: this measurement will permit for the first time a better control of thermal properties of the intergalactic gas, a key factor to address cosmological questions.

On the other hand, the DESI-Lya project will address theoretical developments to prepare the cosmological interpretation of Ly-a data. We will work on optimizing the detection of a signal from neutrino masses, especially improving on the signal robustness in combination with other cosmological probes. Neutrino oscillations tell us that the prospect to measure a non-zero value of Mnu is very plausible, making this study of major interest. We will also model the impact of DM properties on the Ly-a observables: its velocity distribution, self-interactions, etc. This work will expand previous studies, testing new kinds of DM models.

Finally, interpreting the precision, small-scale Ly-a data requires to consequently model the thermal and density properties of the intergalactic medium. This is done with cosmological hydrodynamical simulations. Important methodological progress were made over the past years in order to optimize the usage of this very CPU-intensive tool, permitting to compute precise Ly-a predictions over a large space of cosmological and astrophysical parameters at an affordable CPU cost. Within the DESI-Lya project we will use and optimize these new tools, in particular emulators and optimized hydrodynamical simulations best adapted to the Ly-a forest. Altogether, the DESI-Lya project will lead to unprecedented strong and robust constraint on Mnu from Ly-a data, or to a significant hint of a detection, and to new views on the properties of DM.

Project coordination

Eric ARMENGAUD (Département de Physique des Particules)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.


KIT Karlsruhe Institute of Technology
DPhP Département de Physique des Particules
RWTH Aachen University

Help of the ANR 515,326 euros
Beginning and duration of the scientific project: - 36 Months

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