General bounds on non-standard neutrino interactions (0907.0097v3)

Abstract: We derive model-independent bounds on production and detection non-standard neutrino interactions (NSI). We find that the constraints for NSI parameters are around O(10^{-2}) to O(10^{-1}). Furthermore, we review and update the constraints on matter NSI. We conclude that the bounds on production and detection NSI are generally one order of magnitude stronger than their matter counterparts.

• The paper establishes model-independent bounds on production and detection NSI by analyzing muon decay discrepancies and CKM unitarity tests.
• It employs charged-current analyses, including pion decay universality tests and loop-induced effects, to determine bounds typically in the range O(10^-2)–O(10^-1).
• The findings narrow the parameter space for neutrino oscillation experiments, emphasizing the need to consider non-standard neutrino interactions in future studies.

Overview of General Bounds on Non-Standard Neutrino Interactions

The paper presents a detailed investigation of non-standard neutrino interactions (NSI), seeking to delineate model-independent bounds on both production and detection NSI parameters. This work fills a noticeable gap in existing literature, which previously offered primarily model-dependent bounds.

Core Content and Methodology

The authors focus on NSI affecting neutrino production and detection processes, often referred to as charged-current-like NSI, which involve interactions characterized by charged-current processes tagging neutrino flavors. These interactions are distinct from matter NSI, which involve neutral-current-like operators and have been the focal point of many studies.

A significant portion of the paper is dedicated to deriving bounds from various sources:

1. Kinematic Determination of the Fermi Constant (G_F): By analyzing the discrepancy between the Fermi constant derived from muon decay and its theoretical prediction, the paper extracts bounds on non-standard interactions contributions, primarily leveraging detailed analyses on muon decay processes.
2. CKM Unitarity Tests: The unitarity of the Cabibbo–Kobayashi–Maskawa (CKM) matrix offers a pathway to impose constraints on the leptonic NSI, assuming the preservation of unitarity as predicted by the standard model.
3. Universality Tests from Pion Decay: The comparison of decay rates among charged pions and tau particles provides additional constraints on NSI for processes involving neutrinos of different flavors.
4. Loop Effects and Flavor-Changing Neutral Currents: The paper also investigates the implications of loop-induced constraints, particularly concerning mixings that lead to flavor-changing neutral current processes in charged leptons.

The analysis extends to reviewing and updating constraints on matter NSI, reflecting the paper's comprehensive approach. This includes exploring how these NSI parameters could pertain to neutrino oscillation experiments under various theoretical scenarios.

Key Findings

• The derived constraints for production and detection NSI parameters are generally tighter than for matter NSI, often by about an order of magnitude.
• For charged-current-like NSI, bounds are typically O(10^-2)–O(10^-1) with some parameters exhibiting stronger constraints due to loop-induced phenomena, specifically muon to electron conversion limits.
• The constraints on matter NSI, though weaker, are consolidated from multiple studies, emphasizing the pertinence of NSI in neutrino matter interactions during oscillations.

Implications and Future Directions

The implications of these findings are profound in theoretical and experimental neutrino physics. By establishing stronger, model-independent bounds, this paper contributes significantly to refining the parameter space within which new physics interpretations of neutrino interactions must operate.

Moreover, the derived bounds have practical implications for the design and sensitivity analyses of future neutrino oscillation experiments, especially given that next-generation facilities might probe the scales suggested by these constraints. The work underscores the non-trivial role of production and detection NSI alongside traditional matter effects, thus advocating for inclusive consideration in future phenomenological studies.

Conclusion

The paper represents a pivotal advancement in quantifying bounds on NSI comprehensively and model-independently. It encourages a broader exploration into non-standard interaction scenarios that transcend conventional partial models. While the bounds detailed here set rigorous limits, the potential for observing these interactions at future facilities remains, presenting exciting opportunities for novel discoveries in neutrino physics.