Neutrino Dynamics in Cosmological Contexts

Neutrinos pervade the Universe as relics of the Big Bang, forming a nearly uniform cosmic neutrino background whose properties hold critical clues to the evolution of large-scale structure and fundamental particle physics. Though exceedingly light and weakly interacting, neutrinos influence the growth of cosmic structures through their free-streaming behaviour, damping fluctuations on small scales and imprinting characteristic signatures in the cosmic microwave background and matter power spectrum. As the Universe expands and cools, neutrinos transition from a relativistic regime to one in which their mass becomes dynamically significant, affecting the gravitational potential wells of galaxies and clusters. Their subtle interactions with ordinary matter, along with phenomena such as flavour oscillations, shape both cosmological observables and terrestrial detection strategies. Recent advances in simulation techniques and analytic methods have refined our understanding of neutrino clustering in galactic environments, while laboratory experiments strive to capture direct evidence of the cosmic background. Together, these developments are converging to illuminate the role of neutrinos in the cosmic tapestry, offering prospects for constraining their absolute masses, mass ordering and possible non-standard interactions.

Research from Nature Portfolio

A pioneering study has employed an innovative reweighting method within the N-one-body simulation framework to calculate the present-day density profiles of relic neutrinos in the Milky Way. By reparameterising a single simulation to represent a range of neutrino masses and phase-space distributions, it demonstrated that the local number density contrast scales approximately with the square of the neutrino mass. These findings provide crucial inputs for evaluating the sensitivity of future attempts to detect the cosmic neutrino background in the vicinity of the Earth and establish a benchmark for phenomenological studies of relic neutrino capture.

Neutrino Dynamics in Cosmological Contexts publication trend

The graph below shows the total number of articles in neutrino dynamics in cosmological contexts across all publications each year (not limited to Nature Index journals).

Technical terms

Cosmic Neutrino Background (CνB): A relic sea of neutrinos decoupled from matter shortly after the Big Bang, filling the Universe with a nearly uniform low-energy neutrino field.

Relic neutrinos: Neutrinos that were produced in the early Universe and have cooled to non-relativistic speeds over cosmic time.

Overdensity: The ratio of the local neutrino number density to its average cosmic value, indicating clustering-enhanced densities near massive structures.

Gravitational clustering: The process by which massive neutrinos are drawn into the potential wells of galaxies and dark matter haloes, leading to enhanced local densities.

N-one-body simulation: A computational technique that treats neutrinos as test particles evolving in a fixed gravitational background to estimate their spatial distribution.

Kinetic field theory: An analytical framework for cosmic structure formation that models particles’ trajectories and interactions to predict clustering statistics.

References

1. Limits on the cosmic neutrino background. Journal of Cosmology and Astroparticle Physics (2023).
2. Local clustering of relic neutrinos with kinetic field theory. Physics Letters B (2023).
3. Gravitational clustering of cosmic relic neutrinos in the Milky Way. Nature Communications (2018).