Cosmological probes of dark matter properties
Astrophysics and Astronomy
Final Report Abstract
The properties of Dark Matter are largely unknown. The simplest Dark Matter model predicts that at cosmological times relevant for the study of Cosmic Microwave Background (CMB) anisotropies and for the formation of Large Scale Structures in our universe, Dark Matter particles could be totally decoupled, stable and cold (that is, slow). In reality, the constraints we have from accelerators and from experiments of direct and indirect Dark Matter detection are still perfectly compatible with small Dark Matter scattering rates, self-scattering rates, decay rates, annihilation rates, and even with a small velocity dispersion. When Dark Matter properties are implemented in cosmological simulations, cosmological observables can be used to bound or detect such properties in a range inaccessible to laboratory experiments and astroparticle observations. The goal of this project was to implement a large number of possible nonminimal Dark Matter properties in a unified simulation tool, and then, to perform global fits of Dark Matter parameters to cosmological data. We expanded the simulation code class in order to absorb all these new physical ingredients, and we used it to constrain more Dark Matter models than the previous literature, with newer data and in a more robust way, since we also explored degeneracies among the dark matter parameters or with respect to other extended cosmological parameters. This allowed us to establish stronger and more robust bounds, especially on the Dark Matter scattering rates, self-interaction rate, decay rate and annihilation rate. Among our most striking results: we lowered some bounds on Dark Matter scattering rates by two orders of magnitude thanks to Lyman-α forest data; we ruled out the hypothesis that Dark Mater with multiple scattering rates evades the bounds on individual scattering rates due to parameter degeneracies; we reduced the bounds on Dark Matter decay and primordial Black Hole evaporation thanks to the first joint fit of data on CMB anisotropies and spectral distortions, thanks to the full integration of the calculation of spectral distortions inside the cosmological simulation tool class; and we obtained the first precise constraint on the self-scattering rate of a class of Dark Matter model with a cannibalistic regime, that is, an epoch at which inelastic self-interactions reduce the number of Dark Matter particles. We also inferred stronger bounds on Dark Matter from new techniques at the interface between cosmology and astroparticle physics. We extracted some new information from the auto-correlation and cross-correlation of CMB sky maps from the Planck satellite, γ-ray sky maps from the FERMI satellite and Large Scale Structure maps from various galaxy surveys. This led, for instance, to new bounds on the Dark Matter annihilation cross-section from the non-observation by Planck of a polarised synchrotron signal in the sky caused by Dark Matter annihilation in the Milky Way. The evidence for anomalies in cosmological data has grown over the duration of the project, in particular the “Hubble tension” on the expansion rate of the universe today, and the “S8 tension” on the amplitude of matter fluctuations on inter-galactic scales. These discrepancies between different types of measurements could potentially be solved by new ingredients in the cosmological model. We studied the potential of several Dark Matter model to resolve the tensions. We found several mechanisms that could explain the S8 tension, and showed that at least one of them, involving the scattering of Dark Matter over light relics from the Dark Sector, is an attractive solution, compatible with all estimates of S8 , and at the same time, remarkably, with high-resolution Lyman-α forest data. We showed that a few Dark Matter properties can simultaneously ease the Hubble tension. However, we did not find a convincing explanation of the two anomalies at the same time that would be based on Dark Matter physics. This still leaves open questions for cosmologists. In conclusion, thanks to the study of Dark Matter new models, the development of new simulation tools, the use of new data and the investigation of new observables, we have increased the current knowledge on the possible properties of Dark Matter. This information is precious for model builders, since it helps to discriminate between different set ups of the Dark Sector of particle physics.
Publications
- “Constraining Dark Matter-Dark Radiation interactions with CMB, BAO, and Lyman-α,” JCAP 10 (2019), 055
M. Archidiacono, D. C. Hooper, R. Murgia, S. Bohr, J. Lesgourgues and M. Viel
(See online at https://doi.org/10.1088/1475-7516/2019/10/055) - “The BAO+BBN take on the Hubble tension,” JCAP 10 (2019), 029
N. Schöneberg, J. Lesgourgues and D. C. Hooper
(See online at https://doi.org/10.1088/1475-7516/2019/10/029) - “Cannibalism hinders growth: Cannibal Dark Matter and the S8 tension,” JCAP 12 (2020), 016
S. Heimersheim, N. Schöneberg, D. C. Hooper and J. Lesgourgues
(See online at https://doi.org/10.1088/1475-7516/2020/12/016) - “The synergy between CMB spectral distortions and anisotropies,” JCAP 02 (2020), 026
M. Lucca, N. Schöneberg, D. C. Hooper, J. Lesgourgues and J. Chluba
(See online at https://doi.org/10.1088/1475-7516/2020/02/026) - “Cosmological constraints on multi-interacting dark matter,” JCAP 02 (2021), 019
N. Becker, D. C. Hooper, F. Kahlhoefer, J. Lesgourgues and N. Schöneberg
(See online at https://doi.org/10.1088/1475-7516/2021/02/019) - “Unlocking the synergy between CMB spectral distortions and anisotropies”
H. Fu, M. Lucca, S. Galli, E. S. Battistelli, D. C. Hooper, J. Lesgourgues and N. Schöneberg
(See online at https://doi.org/10.1088/1475-7516/2021/12/050)
