Neutrino Mass and Mixing: from Theory to Experiment (1402.4271v1)

Abstract: The origin of fermion mass hierarchies and mixings is one of the unresolved and most difficult problem in high-energy physics. One possibility to address the flavour problem is by extending the Standard Model to include a family symmetry. In the recent years it has become very popular to use non-Abelian discrete flavour symmetries because of their power in the prediction of the large leptonic mixing angles relevant for neutrino oscillation experiments. Here we give an introduction to the flavour problem and to discrete groups which have been used to attempt a solution for it. We review the current status of models in the light of the recent measurement of the reactor angle and we consider different model building directions taken. The use of the flavons or multi Higgs scalars in model building is discussed as well as the direct vs. indirect approaches. We also focus on the possibility to distinguish experimentally flavour symmetry models by means of mixing sum rules and mass sum rules. In fact, we illustrate in this review the complete path from mathematics, via model building, to experiments, so that any reader interested to start working in the field could use this text as a starting point in order to get a broad overview of the different subject areas.

• The paper introduces discrete symmetry models as a potential solution to the neutrino flavor problem.
• It details how deviations from tri-bi-maximal mixing, reflected in new reactor angle data, redefine theoretical predictions.
• The study integrates theoretical frameworks with experimental tests to predict precise neutrino mass-mixing sum rules.

Neutrino Mass and Mixing: From Theory to Experiment

The paper "Neutrino Mass and Mixing: From Theory to Experiment" offers a comprehensive analysis of the intricate field of neutrino physics, emphasizing the theoretical underpinnings and the experimental results necessary to elucidate the mechanisms behind neutrino masses and mixings. It undertakes a multidisciplinary paper, bridging aspects of theoretical particle physics and the implications of experimental findings, thereby enriching our understanding of fermion mass hierarchies and mixing phenomena.

The Standard Model (SM) establishes the foundational premise, encompassing three families of quarks and leptons, with unique quantum numbers yet displaying different masses. Despite significant advancements, several pressing questions persist, such as the rationale for precisely three families of fermions, the hierarchies in their masses, and the smallness of neutrino masses relative to charged fermions. These form the crux of the "flavour problem."

The paper explores possible solutions by proposing extensions to the SM, notably through the introduction of family symmetries. Discrete non-Abelian symmetries, as the authors suggest, offer a potential pathway for resolving the flavour problem by predicting substantial leptonic mixing angles pertinent to neutrino oscillations. The subsequent discussion on discrete groups, like $S_3$, $S_4$, and $A_4$, explores how these mathematical constructs contribute to theoretical particle physics, especially in establishing the mass hierarchies and mixing matrices that align with experimental observations.

The prevalent picture in neutrino physics has been challenged by recent measurements, notably the reactor angle, debunking the tri-bi-maximal mixing model. This has compelled researchers to reconsider models that permit deviations from tri-bi-maximality, accounting for the newly measured mixing angles within the experimentally observed ranges. The paper evaluates various theoretical directions, including the introduction of flavons or multi-Higgs scalars and differing symmetry breaking approaches, underscoring their theoretical implications and experimental testability.

In the pursuit of distinguishing between various models, the paper discusses potential experimental signatures, focusing on mixing and mass sum rules derived from finite group symmetries that can be verified in future neutrino experiments. These sum rules provide precise predictions that relate mixing angles or mass eigenvalues, offering definitive tests for models based on discrete family symmetries.

Overall, the paper illustrates the theoretical challenges in unifying the diverse criteria for fermion masses and mixings within the framework of the SM with discrete symmetries. It advocates a multipronged approach, combining innovative theoretical models with cutting-edge experimental techniques, to ultimately unravel the complexities of neutrino physics. This integrated approach not only promises to shed light on the fundamental questions in high-energy physics but also paves the way for exploring deeper connections between observable phenomena and underlying symmetry principles in the universe. The prospect of extending these findings to include potential roles for neutrinos in addressing other pivotal topics, such as dark matter or baryogenesis, concurrently underscores the far-reaching implications of solving the flavour problem.