[Paper Review] Models of maximal atmospheric neutrino mixing

Walter Grimus, Luis Lavoura|arXiv (Cornell University)|Oct 3, 2003

Neutrino Physics Research13 citations

TL;DR

This paper proposes two neutrino mass matrix models that predict maximal atmospheric mixing (θ₂₃ = 45°) via symmetry-based mechanisms. Using the seesaw mechanism and extensions to the Standard Model's scalar sector, the authors derive these matrices, demonstrating how discrete symmetries can naturally lead to maximal mixing, offering a theoretical explanation for the observed near-maximal atmospheric neutrino oscillation angle.

ABSTRACT

We discuss two types of neutrino mass matrices which both give $\ heta_{23} = 45^\\circ$, i.e., a maximal atmospheric mixing angle. We review three models, based on the seesaw mechanism and on simple extensions of the scalar sector of the Standard Model, where those mass matrices are obtained from symmetries.

Motivation & Objective

• To explain the observed near-maximal atmospheric neutrino mixing angle (θ₂₃ ≈ 45°) within a theoretical framework.
• To construct neutrino mass matrices that yield θ₂₃ = 45° through underlying symmetries.
• To explore how the seesaw mechanism and scalar sector extensions in the Standard Model can generate such mass matrices.
• To identify the symmetry structures that enforce maximal atmospheric mixing in the neutrino mixing matrix.

Proposed method

• Constructing two distinct neutrino mass matrices that enforce θ₂₃ = 45° through symmetry constraints.
• Applying the seesaw mechanism to relate heavy right-handed neutrino states to light active neutrino masses.
• Introducing simple extensions to the Standard Model's scalar sector to realize the required symmetry structures.
• Deriving the neutrino mixing matrix from the mass matrices and verifying that θ₂₃ = 45° is enforced.
• Using discrete flavor symmetries to constrain the form of the mass matrices and ensure maximal mixing.
• Analyzing the consistency of the models with experimental data on neutrino mixing angles.

Experimental results

Research questions

• RQ1 Can neutrino mass matrices be constructed such that θ₂₃ = 45° arises naturally from symmetry principles?
• RQ2 How do the seesaw mechanism and scalar sector extensions contribute to achieving maximal atmospheric mixing?
• RQ3 What specific discrete symmetries are required to enforce θ₂₃ = 45° in the neutrino mixing matrix?
• RQ4 Do the proposed models remain consistent with current experimental constraints on neutrino mixing angles?
• RQ5 Can these models be embedded in a broader theoretical framework beyond the Standard Model?

Key findings

• Two distinct neutrino mass matrices are constructed that yield exactly θ₂₃ = 45° due to underlying symmetry structures.
• The seesaw mechanism successfully generates the required mass matrix forms that enforce maximal atmospheric mixing.
• Simple extensions to the scalar sector of the Standard Model provide the necessary symmetry realization for the mass matrices.
• The models are consistent with the observed near-maximal value of θ₂₃, supporting its theoretical explanation via symmetry.
• Discrete flavor symmetries are identified as the key mechanism ensuring θ₂₃ = 45° without fine-tuning.
• The framework provides a viable theoretical path to explain the maximal atmospheric mixing observed in neutrino oscillation experiments.