Sterile Neutrinos as the Origin of Dark and Baryonic Matter (1204.3902v2)

Abstract: We demonstrate for the first time that three sterile neutrinos alone can simultaneously explain neutrino oscillations, the observed dark matter and the baryon asymmetry of the Universe without new physics above the Fermi scale. The key new point of our analysis is leptogenesis after sphaleron freeze-out, which leads to resonant dark matter production, evading thus the constraints on sterile neutrino dark matter from structure formation and x-ray searches. We identify the range of sterile neutrino properties that is consistent with all known constraints. We find a domain of parameters where the new particles can be found with present day experimental techniques, using upgrades to existing experimental facilities.

• The paper shows that sterile neutrinos can simultaneously account for dark matter and baryogenesis within the minimal νMSM framework.
• The paper employs resonant leptogenesis to enhance lepton asymmetries, aligning its predictions with Lyα and X-ray constraints.
• The paper delineates an experimentally accessible parameter space, guiding future searches at facilities like CERN SPS and LHCb.

Sterile Neutrinos as the Origin of Dark and Baryonic Matter

The paper authored by Laurent Canetti, Marco Drewes, and Mikhail Shaposhnikov presents a notable exploration into the role of sterile neutrinos in explaining major cosmological observations such as neutrino oscillations, dark matter (DM), and the baryon asymmetry of the Universe (BAU). Here, an in-depth analysis is conducted in the framework of the Neutrino Minimal Standard Model ($\nu$MSM), which supplements the Standard Model (SM) of particle physics with three right-handed neutrinos with masses below the electroweak scale.

Overview of the $\nu$MSM

The $\nu$MSM aims to address the limitations of the SM by incorporating three right-handed neutrinos. These sterile neutrinos provide a potential explanation for the phenomena of neutrino oscillations, the presence of dark matter, and baryogenesis without requiring new physics beyond the Fermi scale. The model capitalizes on a minimalistic approach, adding no new energy scales above the electroweak level and leaving the gauge group of the SM unchanged.

Key Findings

1. Sterile Neutrinos in Cosmology: The paper primarily investigates how sterile neutrinos can account for both DM and BAU. It identifies parameters where sterile neutrinos $N_1$ offer a viable DM candidate and where $N_{2,3}$ facilitate baryogenesis through neutrino oscillations.
2. Leptogenesis Mechanism: The paper emphasizes an innovative approach to DM production via a resonant enhancement of effective lepton asymmetries generated post-sphaleron freeze-out. This mechanism allows for effective production of DM in a manner consistent with Ly$_\alpha$ and x-ray observational constraints.
3. Experimentally Accessible Parameter Space: The research demarcates a set of sterile neutrino properties that are consistent with various experimental constraints. This parameter space can be probed with current experimental facilities through sterile neutrino decay searches. The direct searches at facilities such as CERN SPS, LHCb, and others hold the potential for detection within the identified region.
4. Quantitative Study of Neutrino Abundances: The analysis quantifies the evolution of sterile neutrino abundances from an initial hot big bang condition to a temperature of around 50 MeV. It reconciles these results with bounds from direct neutrino searches and big bang nucleosynthesis.

Implications and Future Directions

The implications of this work are significant as it offers a coherent framework for understanding multiple aspects of particle physics and cosmology that are currently unexplained by the SM. By proposing viable sterile neutrino masses and mixings, the paper sets a foundation for experimental exploration that could potentially lead to the discovery of such neutrinos.

From a theoretical perspective, the model presents a fine-tuning of parameters, especially in the context of the constrained $\nu$MSM, bringing into focus the balance needed between Dirac and Majorana masses to realize the desired DM and BAU phenomena. Practically, this sets a clear path for future research, focusing on refining these predictions and searching for astrophysical and experimental signals of sterile neutrinos.

In summary, the paper meticulously delineates a theoretical and experimental approach to validating the $\nu$MSM's hypotheses, facilitating a more robust understanding of the underlying mechanisms of dark matter and baryonic matter origination. The continuation of such work could significantly advance our comprehension of fundamental physics, bridging gaps between theoretical predictions and empirical evidence.