Fate of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:msub> <mml:mi>θ</mml:mi> <mml:mn>12</mml:mn> </mml:msub> </mml:math> under <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mi>μ</m

The recent Jiangmen Underground Neutrino Observatory (JUNO) measurements of <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"> <a:msub> <a:mi>θ</a:mi> <a:mn>12</a:mn> </a:msub> </a:math> and <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"> <c:mi mathvariant="normal">Δ</c:mi> <c:msubsup> <c:mi>m</c:mi> <c:mn>21</c:mn> <c:mn>2</c:mn> </c:msubsup> </c:math> open a new avenue for probing flavor symmetric structures in the lepton sector. Motivated by this, we study a model in which <f:math xmlns:f="http://www.w3.org/1998/Math/MathML" display="inline"> <f:mi>μ</f:mi> <f:mo>−</f:mo> <f:mi>τ</f:mi> </f:math> reflection symmetry naturally emerges from an underlying <h:math xmlns:h="http://www.w3.org/1998/Math/MathML" display="inline"> <h:msub> <h:mi>A</h:mi> <h:mn>4</h:mn> </h:msub> </h:math> flavor symmetry within a type-II seesaw framework. Beyond its standard predictions of <j:math xmlns:j="http://www.w3.org/1998/Math/MathML" display="inline"> <j:msub> <j:mi>θ</j:mi> <j:mn>23</j:mn> </j:msub> <j:mo>=</j:mo> <j:mn>4</j:mn> <j:mn>5</j:mn> <j:mi>°</j:mi> </j:math> and <l:math xmlns:l="http://www.w3.org/1998/Math/MathML" display="inline"> <l:msub> <l:mi>δ</l:mi> <l:mrow> <l:mi>CP</l:mi> </l:mrow> </l:msub> <l:mo>=</l:mo> <l:mo>±</l:mo> <l:mi>π</l:mi> <l:mo>/</l:mo> <l:mn>2</l:mn> </l:math> , the framework yields testable predictions for <n:math xmlns:n="http://www.w3.org/1998/Math/MathML" display="inline"> <n:msub> <n:mi>θ</n:mi> <n:mn>12</n:mn> </n:msub> </n:math> that can be probed by JUNO. Two viable scenarios arise, one predicting <p:math xmlns:p="http://www.w3.org/1998/Math/MathML" display="inline"> <p:mrow> <p:msup> <p:mrow> <p:mi>sin</p:mi> </p:mrow> <p:mrow> <p:mn>2</p:mn> </p:mrow> </p:msup> <p:msub> <p:mrow> <p:mi>θ</p:mi> </p:mrow> <p:mrow> <p:mn>12</p:mn> </p:mrow> </p:msub> <p:mo>≳</p:mo> <p:mn>0.335</p:mn> </p:mrow> </p:math> , which is strongly disfavored by the latest JUNO results. Correlations between <r:math xmlns:r="http://www.w3.org/1998/Math/MathML" display="inline"> <r:msub> <r:mi>θ</r:mi> <r:mn>12</r:mn> </r:msub> </r:math> and model parameters further enhance the model’s predictivity. Future measurements at DUNE and T2HK will provide complementary tests of this scenario.