Dark Matter Suppression of Structure Constrained by JWST and Lyman-α Forest.

Research demonstrates constraints on low-mass dark matter produced via freeze-in mechanisms, utilising data from Milky Way satellites, gravitational lensing with the James Webb Space Telescope, and the Lyman-α forest. This analysis translates warm dark matter limits into minimum masses for various dark matter candidates, including sterile neutrinos and axion-like particles.

The nature of dark matter remains one of the most compelling puzzles in modern cosmology, with current research increasingly focused on the subtle effects it exerts on the structure of the universe. A new study, published recently, investigates the implications of ‘freeze-in’ production mechanisms for dark matter, particularly at small scales, and establishes novel mass limits for potential particle candidates. Researchers from the University of Padova, including Francesco D’Eramo affiliated with both the Department of Physics and Astronomy and the Istituto Nazionale di Fisica Nucleare (INFN), collaborated with Alessandro Lenoci from the Racah Institute of Physics at the Hebrew University and Cornell University’s Laboratory for Elementary Particle Physics, alongside Ariane Dekker from the Kavli Institute for Cosmological Physics at the University of Chicago. Their work, entitled “Dark Matter Freeze-In and Small-Scale Observables: Novel Mass Bounds and Viable Particle Candidates”, presents a comprehensive analysis utilising recent data from Milky Way satellite counts, strong gravitational lensing observations from the James Webb Space Telescope, and the Lyman-α forest, to constrain the properties of dark matter produced through two-body decays, scatterings, and three-body decays, including scenarios involving Higgs portals, sterile neutrinos, axion-like particles, and dark portals.

Cosmological observations consistently demonstrate that dark matter comprises a substantial fraction of the universe’s energy density, yet its fundamental nature remains unknown. Researchers actively investigate various dark matter candidates and production mechanisms, concentrating on models consistent with both cosmological data and the principles of particle physics. Recent investigations reveal that analysing the suppression of small-scale cosmological structure provides a crucial indicator of dark matter originating from ‘freeze-in’ mechanisms at lower mass ranges, offering a powerful tool for constraining dark matter properties. Freeze-in mechanisms describe a production process where dark matter particles are created very weakly from the decay or annihilation of particles in the standard model, resulting in a low dark matter density.

The study integrates observational constraints from multiple sources, including counts of Milky Way satellite galaxies, strong gravitational lensing data obtained by the James Webb Space Telescope, and measurements of the Lyman-alpha forest. The Lyman-alpha forest consists of absorption lines in the spectra of distant quasars, caused by intervening neutral hydrogen gas, and provides a map of the cosmic web. Combining these datasets provides a robust foundation for assessing the properties of dark matter candidates and testing different theoretical models. Scientists meticulously analyse these observations, searching for subtle signatures that reveal the presence and characteristics of dark matter.

A key methodological approach involves translating existing limits on warm dark matter (WDM) into lower mass boundaries for a diverse range of dark matter candidates exhibiting quasi-thermal phase space distributions. Warm dark matter consists of particles with velocities higher than those predicted by cold dark matter, suppressing the formation of small-scale structures. This strategy offers efficiency and facilitates the exploration of a broad spectrum of theoretical models.

Researchers meticulously model the formation and evolution of cosmic structures, incorporating the effects of both dark matter and baryonic matter – the ordinary matter that makes up stars, planets, and us – to accurately predict the observed distribution of galaxies and other cosmic objects. They then compare these predictions with observational data, searching for discrepancies that might indicate new physics or modifications to the standard cosmological model, known as ΛCDM.

The analysis yields model-independent bounds for dark matter produced through two-body decays, scatterings, and three-body decays. These bounds provide a versatile framework for constraining various production mechanisms, avoiding reliance on specific theoretical assumptions.

Scientists investigate the interplay between different dark matter production mechanisms, exploring the possibility that multiple processes contribute to the observed dark matter abundance. They develop theoretical models that incorporate multiple production channels, accurately predicting the resulting dark matter spectrum and distribution.

Scientists plan to explore the possibility of self-interacting dark matter, where dark matter particles interact with each other through forces other than gravity. They will develop theoretical models that incorporate these interactions, accurately predicting the resulting effects on the distribution of dark matter and the formation of cosmic structures. Such interactions could potentially resolve discrepancies between simulations and observations regarding the density profiles of dark matter halos.

Researchers intend to combine their results with data from other cosmological probes, such as the cosmic microwave background and supernova surveys, to obtain a more complete picture of the universe and its constituents. This multi-probe approach will allow them to break degeneracies between different cosmological parameters and obtain more precise constraints on dark matter models.

Scientists plan to explore the possibility of modified gravity theories, which propose that gravity behaves differently at large scales than predicted by general relativity. They will develop theoretical models that incorporate these modifications, accurately predicting the resulting effects on the formation of cosmic structures and the expansion of the universe.

Future work should focus on refining the modelling of non-linear structure formation to further enhance the precision of the derived constraints. Scientists plan to incorporate more detailed physics into their simulations, accurately accounting for the effects of baryonic matter and feedback processes – such as energy released by supernovae and active galactic nuclei – and improve the resolution of their simulations.

Scientists investigate specific models, including those incorporating self-interactions and modified gravity, consistently validating the accuracy and robustness of the model-independent analysis. The ongoing quest to unravel the nature of dark matter represents a significant challenge for modern physics and cosmology, with future research promising to reveal even more about this mysterious substance and potentially revolutionising our understanding of the cosmos.