- The paper demonstrates that incorporating three sterile neutrinos in the νMSM can explain neutrino oscillations, matter-antimatter imbalance, and a viable dark matter candidate.
- It details a range of experimental approaches, including X-ray observations, Lyman-alpha data, and laboratory searches to constrain sterile neutrino properties.
- The findings suggest that the νMSM offers a minimal yet robust framework that aligns with existing observations while providing testable predictions for physics beyond the Standard Model.
The Role of Sterile Neutrinos in Cosmology and Astrophysics
The paper under discussion, "The Role of Sterile Neutrinos in Cosmology and Astrophysics," presents an in-depth exploration of an extension to the Standard Model (SM) of particle physics known as the Neutrino Minimal Standard Model (νMSM). This model introduces three right-handed, or "sterile," neutrinos with masses below the electroweak scale and purports to explain several phenomena beyond the SM, without resorting to new energy scales beyond the electroweak and Planck scales.
Key Aspects of the νMSM
- Neutrino Oscillations: The νMSM accounts for neutrino flavor oscillations, a phenomenon where neutrinos transition between different flavors, a process unaccounted for in the original SM. The paper discusses right-handed neutrinos as the missing link that explains these oscillations, matching observed mass differences.
- Baryon Asymmetry of the Universe (BAU): The paper outlines a mechanism through which the νMSM can generate the observed baryon asymmetry—the excess of matter over antimatter in the Universe—through the oscillation and decay properties of sterile neutrinos. This includes the detailed dynamics under which singlet fermions contribute to such asymmetry without getting into equilibrium prematurely, hence preserving the generated asymmetry.
- Dark Matter (DM) Candidate: Sterile neutrinos within the νMSM serve as potential dark matter candidates, primarily by satisfying constraints imposed on dark matter, such as being non-baryonic, massive, and weakly interacting. The lightest sterile neutrino plays a dual role by potentially constituting a form of warm dark matter, affecting cosmic structure formation distinctively compared to cold dark matter.
Experimental Verification and Constraints
The authors articulate how the νMSM framework can be tested with current and forthcoming experimental technologies:
- X-ray and Astrophysical Constraints: X-ray observatories, by searching for X-ray signatures from sterile neutrino decay, set upper limits on the mass and mixing angles of sterile neutrinos, while the phase-space density arguments establish lower limits, collectively constraining the νMSM parameter space.
- Lyman-alpha Forest Data: This provides constraints on sub-Mpc scales, elucidating the suppression of power in small-scale structure formation, thus offering additional verification routes for sterile neutrinos within cosmological data sets.
- Laboratory Searches: Future experimental searches at proton accelerators and neutrino facilities can further probe the properties of sterile neutrinos.
Implications and Outlook
The νMSM offers a comprehensive framework that resolves several key issues beyond the SM including neutrino masses, BAU, and a credible dark matter candidate while not invoking new exotic particles at unknown energy scales. From a theoretical standpoint, the νMSM stands out for its minimalistic yet exhaustive approach, enabling exploration of fundamental physics within the constraints of existing experimental observations. However, the tenability of the νMSM is heavily reliant on experimental investigation of sterile neutrinos, which could potentially confirm or rule out the proposed extensions to the SM.
Future explorations may consider the νMSM as a springboard for further extensions, potentially integrating this framework with supersymmetry or grand unified theories. Moreover, the νMSM can interact with current astrophysical phenomena like supernova dynamics and cosmic structure formation, providing avenues for rich interdisciplinary applications. As the νMSM stands as a promising candidate for addressing BSM phenomena, its detailed experimental verification and incorporation into broader particle physics frameworks remain crucial for further advancements in the field.