Phenomenology of the flavor symmetric scoto-seesaw model with dark matter and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi>TM</mml:mi></mml:mrow><mml:mrow><mml:mn>1</mml:mn></mml:mrow

We propose a hybrid scoto-seesaw model based on the <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:msub><a:mi>A</a:mi><a:mn>4</a:mn></a:msub><a:mo>×</a:mo><a:msub><a:mi>Z</a:mi><a:mn>4</a:mn></a:msub><a:mo>×</a:mo><a:msub><a:mi>Z</a:mi><a:mn>3</a:mn></a:msub><a:mo>×</a:mo><a:msub><a:mi>Z</a:mi><a:mn>2</a:mn></a:msub></a:math> non-Abelian discrete flavor symmetry. Light neutrino masses come from the tree-level type-I seesaw mechanism, and from the one-loop scotogenic contribution accommodating viable dark matter candidates responsible for the observed relic abundance of dark matter (DM). These contributions restore the atmospheric and solar neutrino mass scales, respectively. With only one right-handed neutrino, the model features specific predictions with the normal ordering of light neutrino masses, the lightest neutrino being massless, and only one relevant <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"><c:mrow><c:mi>C</c:mi><c:mi>P</c:mi></c:mrow></c:math> Majorana phase. Further, an experimentally favorable <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"><e:mrow><e:msub><e:mrow><e:mi>TM</e:mi></e:mrow><e:mrow><e:mn>1</e:mn></e:mrow></e:msub></e:mrow></e:math> mixing scheme is realized with concrete correlations and constraints on the mixing angles and associated <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline"><g:mrow><g:mi>C</g:mi><g:mi>P</g:mi></g:mrow></g:math> phases. The model predicts the atmospheric mixing angle to be in the upper octant with specific ranges <i:math xmlns:i="http://www.w3.org/1998/Math/MathML" display="inline"><i:mn>0.531</i:mn><i:mo stretchy="false">(</i:mo><i:mn>0.580</i:mn><i:mo stretchy="false">)</i:mo><i:mo>≤</i:mo><i:msup><i:mi>sin</i:mi><i:mn>2</i:mn></i:msup><i:msub><i:mi>θ</i:mi><i:mn>23</i:mn></i:msub><i:mo>≤</i:mo><i:mn>0.544</i:mn><i:mo stretchy="false">(</i:mo><i:mn>0.595</i:mn><i:mo stretchy="false">)</i:mo></i:math>, and the Dirac <o:math xmlns:o="http://www.w3.org/1998/Math/MathML" display="inline"><o:mrow><o:mi>C</o:mi><o:mi>P</o:mi></o:mrow></o:math> phase is restricted within the range <q:math xmlns:q="http://www.w3.org/1998/Math/MathML" display="inline"><q:mrow><q:mo>±</q:mo><q:mo stretchy="false">(</q:mo><q:mn>1.44</q:mn><q:mi>–</q:mi><q:mn>1.12</q:mn><q:mo stretchy="false">)</q:mo><q:mtext> </q:mtext><q:mi>rad</q:mi></q:mrow></q:math>. The Majorana phase is also tightly constrained, with the ranges 0.82–0.95 and 1.58–1.67 rad, which are otherwise unconstrained from neutrino oscillations. Strict predictions on the Majorana phases also yield an accurate prediction for the effective mass parameter for neutrinoless double beta within the range of 1.61–3.85 meV. The model offers a rich phenomenology regarding DM relic density and direct-search constraints, and the fermionic DM scenario has been discussed in detail, estimating its possible connection with the neutrino sector. As an example of the model studies at colliders, the SM Higgs in the diphoton decay channel is examined. The model predicts strictly vanishing <u:math xmlns:u="http://www.w3.org/1998/Math/MathML" display="inline"><u:mi>τ</u:mi><u:mo stretchy="false">→</u:mo><u:mi>e</u:mi><u:mi>γ</u:mi></u:math>, <x:math xmlns:x="http://www.w3.org/1998/Math/MathML" display="inline"><x:mi>τ</x:mi><x:mo stretchy="false">→</x:mo><x:mn>3</x:mn><x:mi>e</x:mi></x:math> decays and testable signals by MEG-II and SINDRUM/Mu3e experiments for the <ab:math xmlns:ab="http://www.w3.org/1998/Math/MathML" display="inline"><ab:mi>μ</ab:mi><ab:mo stretchy="false">→</ab:mo><ab:mi>e</ab:mi><ab:mi>γ</ab:mi></ab:math> and <db:math xmlns:db="http://www.w3.org/1998/Math/MathML" display="inline"><db:mi>μ</db:mi><db:mo stretchy="false">→</db:mo><db:mn>3</db:mn><db:mi>e</db:mi></db:math> decays, respectively. Published by the American Physical Society 2024