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Viability of $A_4$, $S_4$ and $A_5$ Flavour Symmetries in Light of the First JUNO Result

S. T. Petcov, A. V. Titov

TL;DR

This work evaluates the viability of lepton mixing scenarios generated by residual Abelian symmetries of $A_4$, $S_4$ and $A_5$ in light of JUNO's first measurement of $\sin^2\theta_{12}$ and the NuFIT v6 global neutrino oscillation fit. The authors derive explicit sum rules for $\sin^2\theta_{12}$ and $\cos\delta$ for patterns associated with TM1 (B2S4) and TM2 (B1), and identify which patterns remain compatible at $3\sigma$ after incorporating JUNO. The analysis shows that JUNO dramatically reduces viable patterns from five (NO) and four (IO) to three (NO) and two (IO), with TM1 (B2S4) emerging as the most favored scenario, while CP-phase predictions remain sensitive to $\theta_{23}$ uncertainties. The results imply that forthcoming JUNO measurements and precision determinations of $\delta$ will stringently test these discrete symmetry-based mixing patterns and potentially discriminate TM1 from competing realizations.

Abstract

We update the analysis of the viability of the lepton mixing patterns originating from $A_4$, $S_4$ and $A_5$ discrete flavour symmetries and leading to predictions for the solar neutrino mixing angle, $θ_{12}$. We perform a statistical analysis using as an input (i) the results of the latest global fit to neutrino oscillation data, and (ii) the first JUNO measurement of $\sin^2θ_{12}$. Out of the five (four) cases compatible with the global data at $3σ$ for normal (inverted) neutrino mass ordering, only three (two) cases remain compatible with the global data at the same confidence level after taking into account the JUNO result.

Viability of $A_4$, $S_4$ and $A_5$ Flavour Symmetries in Light of the First JUNO Result

TL;DR

This work evaluates the viability of lepton mixing scenarios generated by residual Abelian symmetries of , and in light of JUNO's first measurement of and the NuFIT v6 global neutrino oscillation fit. The authors derive explicit sum rules for and for patterns associated with TM1 (B2S4) and TM2 (B1), and identify which patterns remain compatible at after incorporating JUNO. The analysis shows that JUNO dramatically reduces viable patterns from five (NO) and four (IO) to three (NO) and two (IO), with TM1 (B2S4) emerging as the most favored scenario, while CP-phase predictions remain sensitive to uncertainties. The results imply that forthcoming JUNO measurements and precision determinations of will stringently test these discrete symmetry-based mixing patterns and potentially discriminate TM1 from competing realizations.

Abstract

We update the analysis of the viability of the lepton mixing patterns originating from , and discrete flavour symmetries and leading to predictions for the solar neutrino mixing angle, . We perform a statistical analysis using as an input (i) the results of the latest global fit to neutrino oscillation data, and (ii) the first JUNO measurement of . Out of the five (four) cases compatible with the global data at for normal (inverted) neutrino mass ordering, only three (two) cases remain compatible with the global data at the same confidence level after taking into account the JUNO result.

Paper Structure

This paper contains 6 sections, 13 equations, 2 figures, 1 table.

Table of Contents

  1. Introduction.
  2. Mixing patterns predicting $\sin^2\theta_{12}$.
  3. Statistical analysis.
  4. Results.
  5. Summary and conclusions.
  6. Acknowledgements.

Figures (2)

  • Figure 1: Upper panels: predictions for $\sin^2\theta_{12}$ obtained using the results of the global analysis of neutrino oscillation data performed by the NuFIT collaboration in September 2024 Esteban:2024eliNuFITv6Sep2024. Lower panels: the same after including the first JUNO measurement from November 2025 JUNO:2025gmd. The black dashed line corresponds to the one-dimensional projection $\chi^2_1(\sin^2\theta_{12})$ obtained by NuFIT, whereas the black dotted line corresponds to $\chi^2_\mathrm{1,\,JUNO}(\sin^2\theta_{12})$ in eq. \ref{['eq:chi2ss12JUNO']}.
  • Figure 2: Upper panels: predictions for $\cos\delta$ obtained using the results of the global analysis of neutrino oscillation data performed by the NuFIT collaboration in September 2024 Esteban:2024eliNuFITv6Sep2024. Lower panels: the same after including the first JUNO measurement from November 2025 JUNO:2025gmd. The black dashed line corresponds to the one-dimensional projection $\chi^2_4(\delta)$ obtained by NuFIT.