Programme

P.79 -- Posters, VCTP-50

Date: Thursday, 7 August 2025

Time: 08:30 - 10:00

Study of Neutrino Masses from an A₄-Based Seesaw Model

Tran Tien Manh(1), Phan To Quyen(2), Nguyen Anh Ky(1), Phi Quang Van(1)

(1) Institute of physics(IOP), (2)International Centre for Interdisciplinary Science and Education (ICISE)

In this study, we investigate the origin of neutrino masses and the mechanism of CP violation in the lepton sector by constructing a Standard Model extension based on the discrete non-Abelian flavor symmetry group \textbf{A$_4$}. The model introduces three generations of right-handed neutrinos and an extended scalar sector composed of one A$_4$ triplet Higgs and three scalar singlets, allowing for a realistic mass structure in the lepton sector. Neutrino masses are generated via a \textbf{Type-I Seesaw mechanism}, with the Dirac and Majorana mass matrices derived explicitly from the model’s Yukawa Lagrangian. Perturbative analysis around the tribimaximal (TBM) mixing limit is performed, introducing small corrections through symmetry-breaking parameters \( \epsilon_+ \) and \( \epsilon_- \). Analytical expressions for neutrino mass eigenvalues, mixing angles, and the Dirac CP phase \( \delta_{CP} \) are obtained in terms of model parameters. The model successfully predicts: \begin{itemize} \item Neutrino mass spectrum in the normal ordering with \( m_1, m_2 , m_3 ~ \text{at eV level} \), \item The sum of neutrino masses \( \sum m_\nu < 0.12\,\text{eV} \), consistent with cosmological bounds, \item An effective neutrino mass in beta decay \( m_\beta \approx 0.010\,\text{eV} \), \item An effective Majorana mass for neutrinoless double beta decay \( m_{\beta\beta} \approx 2.9\,\text{meV} \), \item A maximum Jarlskog invariant \( |J_{CP}^{\text{max}}| \approx 0.02 \), compatible with current experimental ranges. \end{itemize} The model also establishes predictive sum rules relating mass eigenstates and provides analytical constraints on the Dirac CP phase using modified PMNS matrix elements. The results show good agreement with recent neutrino oscillation data and offer a compelling framework for interpreting future experimental results, especially from precision measurements of CP violation and rare lepton-number-violating processes.

Presenter: Tran Tien Manh