Non standard neutrino interactions

Abstract: Neutrino oscillations have become well-known phenomenon; the measurements of neutrino mixing angles and mass squared differences are continuously improving. Future oscillation experiments will eventually determine the remaining unknown neutrino parameters, namely, the mass ordering, normal or inverted, and the CP-violating phase. On the other hand, the absolute mass scale of neutrinos could be probed by cosmological observations, single beta decay as well as by neutrinoless double beta decay experiments. Furthermore, the last one may shed light on the nature of neutrinos, Dirac or Majorana, by measuring the effective Majorana mass of neutrinos. However, the neutrino mass generation mechanism remains unknown. A well-motivated phenomenological approach to search for new physics, in the neutrino sector, is that of non-standard interactions. In this short review, the current constraints in this picture, as well as the perspectives from future experiments, are discussed.

• The paper reviews state-of-the-art constraints on NSI parameters and discusses their role in extending the standard three-neutrino framework.
• It analyzes data from solar, atmospheric, and accelerator experiments, including contributions from Super-Kamiokande and MINOS, to set bounds on NSI effects.
• Future experiments like Hyper-Kamiokande and LBNE are highlighted as key to distinguishing NSI effects from standard oscillations and uncovering new physics.

Non-Standard Neutrino Interactions: Present Status and Future Prospects

The paper by Miranda and Nunokawa provides a comprehensive review of the current understanding and future directions of research on non-standard neutrino interactions (NSI). Neutrino oscillations are well-documented phenomena, and substantial progress has been made in determining neutrino mixing angles and mass-squared differences. However, several neutrino parameters remain undetermined, including mass ordering and the CP-violating phase. Furthermore, the absolute neutrino mass scale and the Dirac or Majorana nature of neutrinos represent ongoing areas of research. A phenomenological approach to exploring new physics in the neutrino sector is through NSI.

Current Understanding

The standard three-neutrino oscillation framework has greatly improved our understanding of neutrino properties, with most parameters now measured with significant accuracy. Nevertheless, the standard model does not account for potential extra interactions that could indicate physics beyond the Standard Model. NSI, if present, would interact via a four-fermion Lagrangian. The parameters within this framework describe NSI strength and differ based on whether they occur at the source, during propagation, or at detection.

NSI could lead to matter effects differing from those predicted by the MSW effect. Propagation effects such as those encountered in solar, atmospheric, and long-baseline experiments play a crucial role in constraining NSI parameters. The comparison of experimental cross-section measurements with theoretical predictions provides a way to determine the presence of NSI. Constraints are provided for neutrino interaction with electrons and quarks through non-oscillation experiments.

Experimental Results and Constraints

Past and current experimental data provide constraints on the NSI parameters. Bounds derived from atmospheric, solar, accelerator, and reactor neutrino experiments are well-documented. For example, the Super-Kamiokande and MINOS collaborations have contributed significantly to these constraints. Challenges arise in differentiating potential NSI contributions from standard neutrino oscillation parameters and in exploring new models for physics beyond the Standard Model.

Implications and Future Prospects

The paper discusses various models that could manifest NSI: extended gauge symmetries, additional neutral leptons, and additional scalars. Each model allows for different expressions of NSI and could have phenomenological consequences detectable in experiments.

Future experimental venues like Hyper-Kamiokande, LBNE, and next-generation neutrino telescopes expand the possibilities for detecting or further constraining NSI. The potential for detecting NSI in future experiments could advance understanding of neutrino properties and fundamental physics. Avenues for distinguishing between standard and non-standard physics in experimental setups are imperative.

Conclusion

The exploration of NSI stands as a cautious yet promising path toward uncovering new physics. The intersection of current experimental precision and theoretical advances could transform our understanding of neutrino dynamics and interactions. As future experiments come online, they will refine these constraints or potentially reveal evidence of new physics, providing profound implications for our comprehension of fundamental particles and their interactions.