Dark Matter, Baryogenesis and Neutrino Oscillations from Right Handed Neutrinos (1208.4607v2)

Abstract: We show that, leaving aside accelerated cosmic expansion, all experimental data in high energy physics that are commonly agreed to require physics beyond the Standard Model can be explained when completing it by three right handed neutrinos that can be searched for using current day experimental techniques. The model that realises this scenario is known as Neutrino Minimal Standard Model (\nu MSM). In this article we give a comprehensive summary of all known constraints in the \nu MSM, along with a pedagogical introduction to the model. We present the first complete quantitative study of the parameter space of the model where no physics beyond the \nu MSM is needed to simultaneously explain neutrino oscillations, dark matter and the baryon asymmetry of the universe. This requires to track the time evolution of left and right handed neutrino abundances from hot big bang initial conditions down to temperatures below the QCD scale. We find that the interplay of resonant amplifications, CP-violating flavour oscillations, scatterings and decays leads to a number of previously unknown constraints on the sterile neutrino properties. We furthermore re-analyse bounds from past collider experiments and big bang nucleosynthesis in the face of recent evidence for a non-zero neutrino mixing angle \theta_{13}. We combine all our results with existing constraints on dark matter properties from astrophysics and cosmology. Our results provide a guideline for future experimental searches for sterile neutrinos. A summary of the constraints on sterile neutrino masses and mixings has appeared in arXiv:1204.3902 [hep-ph]. In this article we provide all details of our calculations and give constraints on other model parameters.

• The paper demonstrates that the νMSM, incorporating three right-handed neutrinos, offers a unified model for dark matter, baryogenesis, and neutrino oscillations.
• The study rigorously maps the parameter space, identifying viable mass ranges and mixing angles that align with cosmological and neutrino oscillation data.
• The results provide testable predictions for future experiments, linking resonant production mechanisms with the observed dark matter and baryon asymmetry.

Overview of Dark Matter, Baryogenesis, and Neutrino Oscillations from Right-Handed Neutrinos

The paper by Canetti et al. explores the potential of complementing the Standard Model (SM) of particle physics with three right-handed neutrinos to address pivotal cosmological and particle physics phenomena: dark matter, baryogenesis, and neutrino oscillations. This framework is known as the Neutrino Minimal Standard Model (νMSM). The νMSM introduces three additional neutrino species, the sterile neutrinos, which are singlets under the SM gauge group and provide a minimal extension aimed at tackling physics beyond the SM without invoking new principles or high-energy scales.

Key Contributions and Findings

1. Model Specification and Parameter Space

The νMSM is characterized by 18 new parameters, three sterile neutrino masses, and their mixing parameters, complementing the SM without altering its gauge group or introducing new high-energy scales. The paper performs a comprehensive quantitative paper of the parameter space, delineating regions where simultaneous explanations for dark matter, baryogenesis, and neutrino oscillations are feasible without resorting to physics beyond the νMSM.

2. Dark Matter Production

In this framework, the lightest sterile neutrino can serve as a candidate for dark matter, produced in the early universe via the Shi-Fuller resonant enhancement mechanism in the presence of lepton asymmetries. The paper identifies the viable parameter space for the masses and couplings of the lightest sterile neutrino, constrained by indirect observations such as X-ray emissions, large-scale structure, and Lyα forest data.

3. Baryogenesis Mechanism

The νMSM facilitates baryogenesis through the oscillations of the two heavier sterile neutrinos. These oscillations occur before SM sphalerons freeze out, enabling the generation of a baryon asymmetry during a non-equilibrium process. The paper maps out the regions in the parameter space where the generated asymmetry agrees with the observed baryon-to-photon ratio, allowing for successful leptogenesis fronted by flavor oscillations.

4. Neutrino Masses and Mixing

The model ensures that the active neutrinos acquire small masses via the seesaw mechanism with the appropriate eigenvalues and lepton mixing matrix parameters that fit neutrino oscillation data (indicating a quasi-degenerate mass spectrum for the two heavy sterile species).

Practical and Theoretical Implications

- Experimental Searches

The model poses definitive predictions for the masses and mixing of the sterile neutrinos, some of which are within reach of upcoming experimental techniques in high-energy physics, providing testable predictions for future or current experimental setups, such as proton beam dumps and meson decay experiments.

- Universe Composition Insights

By aligning the cosmological abundance of dark matter and baryons predicted by the νMSM with current observations, the model can naturally account for the near equality of baryonic and dark matter densities, presenting an intriguing unified mechanism for these components of the universe.

Conclusion and Speculation on Future Directions

While the νMSM addresses several current anomalies requiring physics beyond the SM in a minimalist manner, challenges remain, such as the extent of fine-tuning required for parameter alignment—specifically the near-degeneracy needed amongst two sterile neutrino masses for resonant production mechanisms. Future research could focus on bridging these theoretical gaps and harnessing the model’s unique predictions to further push the boundaries of both collider and astrophysical experimental frontiers.

The presented paper establishes the νMSM as a viable and insightful candidate for addressing multiple cosmological phenomena within the limits of current physics, warranting further exploration and empirical investigation.