Zooming in on `bi-large' neutrino mixing with the first JUNO results

TL;DR

The paper investigates bi-large lepton mixing patterns in light of JUNO's first results for $\sin^2\theta_{12}$ and $\Delta m^2_{21}$, and tests four CKM-like charged-lepton corrected schemes (T1–T4) against global fits. It derives the predicted correlations among $\theta_{12}$, $\theta_{13}$, $\theta_{23}$, and the Dirac CP phase $\delta$ and examines their viability with JUNO precision. With JUNO data, T1 is pushed toward the higher octant and yields two CP-branch predictions around $\delta \approx 0.7\pi$ or $1.3\pi$, while T2 favors near-maximal $\theta_{23}$ and disfavors CP conservation; T3 and T4 are severely constrained and will be decisively tested with future measurements of $\sin^2\theta_{23}$ and $\delta$. The work also updates expectations for neutrinoless double beta decay via the effective Majorana mass $\langle m_{\beta\beta}\rangle$, showing JUNO tightens the allowed region but does not uniquely determine the Majorana phase sector.

Abstract

The leptonic mixing matrix is examined within bi-large mixing patterns and confronted with the latest results announced by the Jiangmen Underground Neutrino Observatory (JUNO). We analyze the viability of bi large mixing schemes and assess JUNO's ability to test neutrino mixing and discriminate among different bi-large mixing patterns, some of which are strongly disfavored when compared with neutrino oscillation global-fit results. Specific octant and CP predictions emerge. Finally, we comment on the implications of JUNO's findings for neutrinoless double beta decay.

Figures (4)

• Figure 1: Status of bi-large mixing pattern given the global oscillation fit in deSalas:2020pgw10.5281/zenodo.4726908. The red, blue, magenta, and cyan branches correspond to the T1, T2, T3, and T4 patterns, respectively.
• Figure 2: The dashed black line gives to the best fit value of $\sin^2\theta_{12}$ from JUNO with the corresponding $1\sigma$, $3\sigma$ ranges shown in green and orange, respectively. The allowed $3\sigma$ C.L. global-fit parameters are shown in dark gray, with the $1\sigma$, $2\sigma$ regions also displayed and the global best-fit marked (black dot). JUNO's potential to test the T1/T2 bi-large schemes is seen by comparing the red/blue regions with JUNO and global-fit results. See text for details.
• Figure 3: Same as Fig. \ref{['fig:T1']}, but for type T3 (magenta color) and T4 (cyan color).
• Figure 4: Effective Majorana neutrino mass parameter $\langle m_{\beta \beta}\rangle$ as a function of the lightest active neutrino mass $m_1$ for normal ordering. The left panel compares the allowed $\langle m_{\beta \beta}\rangle$ region for a generic scheme before and after JUNO's results, shown in light and dark purple, respectively. The right panel compares the T1 bi-large pattern (in red) with the JUNO results (dark purple). The current KamLAND-Zen limit and the projected sensitivities including JUNO are also indicated. The limit on $m_1$ from cosmology is shown in vertical gray band; see text for details.