- The paper demonstrates that a significant lepton asymmetry induced by resonant νMSM oscillations can produce sterile neutrinos that account for the observed dark matter relic density.
- The paper employs quantum field theory to compute the momentum distribution of keV-scale sterile neutrinos, matching theoretical predictions with astrophysical data.
- The paper highlights that robust lepton asymmetry helps bypass X-ray and Lyman-alpha constraints, establishing sterile neutrinos as viable warm dark matter candidates.
Sterile Neutrino Dark Matter and Lepton Asymmetry in the νMSM
The paper authored by Mikko Laine and Mikhail Shaposhnikov provides an exploration into the thermodynamic and cosmic implications of predicting sterile neutrino dark matter using the framework of the Neutrino Minimal Standard Model (νMSM). The work explores the mechanism of dark matter production through the lepton asymmetry induced by the νMSM and explores the astrophysical consequences of sterile neutrino dark matter.
Model and Theoretical Foundations
The νMSM extends the Standard Model by incorporating three right-handed neutrinos with masses below the electroweak scale. This extension allows the νMSM to potentially explain several cosmological phenomena that the Standard Model cannot, such as dark matter, baryon asymmetry, and neutrino oscillations. The paper focuses on sterile neutrinos, particularly the lightest right-handed neutrinos in the keV mass range, as a viable dark matter candidate.
In this model, CP-violating resonant oscillations among the heavier right-handed neutrinos produce a significant lepton asymmetry, which persists below the sphaleron freeze-out temperature. The lepton asymmetry enhances the production of the lightest right-handed sterile neutrinos through a resonant mechanism, originally suggested by Shi and Fuller. The authors employ quantum field theory methods to calculate the relic density and momentum distribution of these sterile neutrinos under significant lepton asymmetry conditions.
Numerical Results and Boundaries
The paper presents a recalculation of dark matter relic density and sterile neutrino distribution, matching the predictions against existing astrophysical data to derive constraints on their properties. The paper highlights that mechanisms which depend heavily on non-equilibrated, resonant processes could feasibly produce enough sterile neutrinos to account for observed dark matter without conflicting existing observational constraints.
One of the key results is that a sufficiently large lepton asymmetry, in the order of nνe/s∼0.8×10−5, can ensure that sterile neutrinos constitute the full dark matter abundance, corroborated with scenarios demonstrating a range of viable sterile neutrino masses. These findings are contingent on the assumption that a substantial lepton asymmetry not only circumvents X-ray constraints from decaying particles but also meets structural formation limitations posed by Lyman-alpha forest studies.
Implications and Conclusion
The research illustrates that sterile neutrinos, under the νMSM framework with substantial lepton asymmetry, can satisfy both cosmic and structural constraints necessary for them to be considered as viable warm dark matter candidates. The conclusions address the interplay between theoretical particle physics models and cosmological observations, reinforcing the need for specific parameter spaces in the νMSM to explain dark matter entirely through sterile neutrinos.
Unless structure formation simulations become more accurate in integrating non-equilibrium distributions, reliance on simplified interpretations such as those currently used will persist. Nonetheless, the opportunity to experimentally detect sterile neutrinos remains challenging, primarily due to their small coupling constants. The possibility of detecting diffuse X-ray emissions from dark matter decays present the most realistic chance within the foreseeable future. Further research must continue exploring these neutrinos via both experimental detection strategies and more refined simulations of cosmic structure formation.