<p>Implementing the axion concept in the context of 3-3-1 extensions of the Standard Model leads to richer properties than in the simpler axion setups, and they are related to the Dirac neutrino seesaw mechanism. In this way, the smallness of neutrino masses, the strong <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>C</mi><mi>P</mi></mrow></math> problem, the nature of dark matter, and the number of families all have a common origin. Besides having an enhanced coupling to photons, our revamped axion can also be distinguished from both Dine-Fischler-Srednicki-Zhitnisky and Kim-Shifman-Vainshtein-Zakharov axions through its couplings to fermions. The latter lead to interesting phenomenological consequences, including flavor-changing axion-emitting two-body <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>K</mi></math>, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>B</mi></math>, and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>D</mi></math> meson decays.</p>

Spain

Anirban Karan

Julio Leite

José W.F. Valle

Flavor-changing axions and Dirac neutrino masses

<p>Motivated by the recent Belle II result indicating a <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>2.7</mn><mi>σ</mi></math> excess of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>B</mi><mo>+</mo></msup><mo stretchy="false">→</mo><msup><mi>K</mi><mo>+</mo></msup><mo>+</mo><msub><mi>E</mi><mrow><mi>miss</mi></mrow></msub></math> events compared to the Standard Model (SM) prediction for <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>B</mi><mo>+</mo></msup><mo stretchy="false">→</mo><msup><mi>K</mi><mo>+</mo></msup><mi>ν</mi><mover accent="true"><mi>ν</mi><mo stretchy="false">¯</mo></mover></math>, we explore an explanation to this anomaly based on a Kim-Shifman-Vainshtein-Zakharov-type QCD axion model featuring a Peccei-Quinn (PQ) symmetry breaking at high scale, which can provide a solution to the strong <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>C</mi><mi>P</mi></math> problem with dark matter relic abundance. The model contains a PQ-charged scalar leptoquark which can interact with the SM quarks only via mass mixing of the latter with vectorlike quarks. The mixing between SM and vectorlike quarks is determined by the PQ mass scales and can explain the excess <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>B</mi><mo>+</mo></msup><mo stretchy="false">→</mo><msup><mi>K</mi><mo>+</mo></msup><mo>+</mo><msub><mi>E</mi><mrow><mi>miss</mi></mrow></msub></math> events while respecting other flavor constraints. The same PQ-charged scalar leptoquarks and vectorlike quarks also mediate the two-loop radiative neutrino masses.</p>

Chandan Hati

Newton Nath

QCD axion, color-mediated neutrino masses, and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>B</mi><mo>+</mo></msup><mo stretchy="false">→</mo><msup><mi>K</mi><mo>+</mo></msup><mo>+</mo><msub><mi>E</mi><mrow><mi>miss</mi></mrow></msub></math> anomaly

Small neutrino masses can be sourced by a tiny vacuum expectation value of a leptophilic Higgs doublet, and mediated by Quasi-Dirac heavy neutrinos. In such simplest linear seesaw picture the neutrino mass mediators can be accessible to colliders. We describe novel charged Higgs and heavy neutrino production mechanisms that can be sizeable at <math><msup><mrow><mi>e</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>e</mi></mrow><mrow><mo>−</mo></mrow></msup></math>, <math><msup><mrow><mi>e</mi></mrow><mrow><mo>−</mo></mrow></msup><mi>γ</mi></math>, pp, or muon colliders and discuss some of the associated signatures. The oscillation length of the heavy neutrino mediators is directly related to the light neutrino mass ordering. Moreover, lepton number violation can be large despite the smallness of neutrino masses, and may shed light on the Majorana nature of neutrinos and the significance of basic symmetries in weak interaction.

India

Portugal

Aditya Batra

Praveen Bharadwaj

South Korea

Sanjoy Mandal

Rahul Srivastava

Large lepton number violation at colliders: Predictions from the minimal linear seesaw mechanism

The simplest linear seesaw mechanism can accommodate the new CDF-II <italic>W</italic> mass measurement. In addition to Standard Model particles, the model includes quasi-Dirac leptons, and a second, leptophilic, scalar doublet seeding small neutrino masses. Our proposal is consistent with electroweak precision tests, neutrino physics, rare decays and collider restrictions, requiring a new charged scalar below a few TeV, split in mass from the new degenerate scalar and pseudoscalar neutral Higgs bosons.

W-mass anomaly in the simplest linear seesaw mechanism

China

Gui-Jun Ding

Jun-Nan Lu

Corrigendum to “Trimaximal neutrino mixing from scotogenic family symmetry” [Phys. Lett. B 815 (2021) 136122]

We propose that neutrino masses are “seeded” by a dark sector within the inverse seesaw mechanism. This way we have a new, “hidden”, variant of the scotogenic scenario for radiative neutrino masses. We discuss both explicit and dynamical lepton number violation. In addition to invisible Higgs decays with majoron emission, we discuss in detail the pheneomenolgy of dark matter, as well as the novel features associated to charged lepton flavour violation, and neutrino physics.

Chile

Nicolás Rojas

Dark matter as the origin of neutrino mass in the inverse seesaw mechanism

We propose a flavor theory of leptons implementing an <math><msub><mrow><mi>A</mi></mrow><mrow><mn>4</mn></mrow></msub></math> family symmetry. Our scheme provides a simple way to derive trimaximal neutrino mixing from first principles, leading to simple and testable predictions for neutrino mixing and CP violation. Dark matter mediates neutrino mass generation, as in the simplest scotogenic model.

Trimaximal neutrino mixing from scotogenic Family Symmetry

We analyze the consistency of electroweak breaking, neutrino and dark matter phenomenology within the simplest scoto-seesaw model. By adding the minimal dark sector to the simplest “missing partner” type-I seesaw one has a physical picture for the neutrino oscillation lengths: the “atmospheric” mass scale arises from the tree-level seesaw, while the “solar” scale is induced radiatively, mediated by the dark sector. We identify parameter regions consistent with theoretical constraints, as well as dark matter relic abundance and direct detection searches. Using two-loop renormalization group equations we explore the stability of the vacuum and the consistency of the underlying dark parity symmetry. One also has a lower bound for the neutrinoless double beta decay amplitude.

The simplest scoto-seesaw model: WIMP dark matter phenomenology and Higgs vacuum stability

We analyze a model with unbroken <math><mi>U</mi><msub><mrow><mo>(</mo><mn>1</mn><mo>)</mo></mrow><mrow><mi>B</mi><mo>−</mo><mi>L</mi></mrow></msub></math> gauge symmetry where neutrino masses are generated at one loop, after spontaneous breaking of a global <math><mi>U</mi><msub><mrow><mo>(</mo><mn>1</mn><mo>)</mo></mrow><mrow><mi>G</mi></mrow></msub></math> symmetry. These symmetries ensure dark matter (DM) stability and the Diracness of neutrinos. Within this context, we examine fermionic dark matter. Consistency between the required neutrino mass and the observed relic abundance indicates dark matter masses and couplings within the reach of direct detection experiments.

Carlos Alvarado

Cesar Bonilla

Brazil

Phenomenology of fermion dark matter as neutrino mass mediator with gauged B-L

We generalize the idea of the axion to an extended electroweak gauge symmetry setup. We propose a minimal axion extension of the Singer-Valle-Schechter (SVS) theory, in which the standard model fits in <math><mi>SU</mi><msub><mrow><mo>(</mo><mn>3</mn><mo>)</mo></mrow><mrow><mi>L</mi></mrow></msub><mo>⊗</mo><mi>U</mi><msub><mrow><mo>(</mo><mn>1</mn><mo>)</mo></mrow><mrow><mi>X</mi></mrow></msub></math>, the number of families results from anomaly cancellation, and the Peccei-Quinn (PQ) solution to the strong-CP problem is implemented. Neutrino masses arise from a type-I Dirac seesaw mechanism, suppressed by the ratio of SVS and PQ scales, suggesting the existence of new physics at a moderate SVS scale. Novel features include an enhanced axion coupling to photons when compared to the DFSZ axion, as well as flavor-changing axion couplings to quarks.