We study a realistic SU(5) grand unified model, where a <math><mrow><mn>45</mn></mrow></math> representation of scalar fields is added to the Georgi-Glashow model in order to realize the gauge coupling unification and the masses and mixing of quarks and leptons. The gauge coupling unification together with constraints from proton decay implies mass splittings in scalar representations. We assume that an SU(2) triplet component of the <math><mrow><mn>45</mn></mrow></math> scalar, which is called <math><msub><mi>S</mi><mn>3</mn></msub></math> leptoquark, has a TeV-scale mass, and color-sextet and color-octet ones have masses of the order of <math><msup><mn>10</mn><mn>6</mn></msup><mtext> </mtext><mtext> </mtext><mi>GeV</mi></math>. We calculate one-loop beta functions for Yukawa couplings in the model, and derive the low-energy values of the <math><msub><mi>S</mi><mn>3</mn></msub></math> Yukawa couplings which are consistent with the grand unification. We provide predictions for lepton-flavor violation and lepton-flavor-universality violation induced by the <math><msub><mi>S</mi><mn>3</mn></msub></math> leptoquark, and find that current and future experiments have a chance to find a footprint of our SU(5) model.

Japan

Toru Goto

Satoshi Mishima

Tetsuo Shindou

Flavor physics in SU(5) GUT with scalar fields in the 45 representation

We show that three open questions in particle physics and cosmology: the origin of neutrino mass, the identity of dark matter, and the origin of the baryon asymmetry of the universe can be explained simultaneously in the three-loop seesaw model proposed by Krauss, Nasri, and Trodden. We discuss the difficulty of successful leptogenesis with three right-handed neutrinos, and we propose a scenario with four right-handed neutrinos that satisfies all observational constraints. This scenario predicts a sleptonlike particle as light as a few hundreds GeV that can be probed by future collider experiments.

Osamu Seto

Takanao Tsuyuki

Low-scale leptogenesis and dark matter in a three-loop radiative seesaw model

We study the lepton flavor violating decays such as <math><mi>μ</mi><mo>→</mo><mi>e</mi><mi>γ</mi></math>, <math><mi>τ</mi><mo>→</mo><mi>e</mi><mi>γ</mi></math>, <math><mi>τ</mi><mo>→</mo><mi>μ</mi><mi>γ</mi></math> in the three-loop radiative seesaw model proposed by Krauss, Nasri, and Trodden. In this model, the relevant coupling constants are larger for the heavier scalars that run inside loop diagrams to generate the appropriate magnitude of neutrino masses. Imposing a criterion that all the coupling constants must be small enough to be treated perturbatively, we find an upper bound on the mass of one of the scalars. By combining it with neutrino mass parameters, we derive lower bounds on the branching ratios of the lepton flavor violating processes. In a case with the inverted mass ordering and best-fit neutrino oscillation parameters, one of the lower bounds is <math><mi>Br</mi><mo>(</mo><mi>μ</mi><mo>→</mo><mi>e</mi><mi>γ</mi><mo>)</mo><mo>&gt;</mo><mn>1.1</mn><mo>×</mo><msup><mn>10</mn><mrow><mo>−</mo><mn>13</mn></mrow></msup></math>, which is within the reach of the MEG II experiment.

Lower bounds on lepton flavor violating branching ratios in a radiative seesaw model

Though models with the radiative neutrino mass generation are phenomenologically attractive, the complicated relationship between the flavour structure of additional Yukawa matrices and the neutrino mass matrix sometimes is a barrier to explore the models. We introduce a simple prescription to analyze the relation in a class of models with the asymmetric Yukawa structure. We then apply the treatment to the Zee-Babu model as a concrete example of the class and discuss the phenomenological consequences of the model. The combined studies among the neutrino physics, the lepton flavour violation, and the search for the new particles at the collider experiments provide the anatomy of the Zee-Babu model.

Yoko Irie

Lepton flavour violation in a radiative neutrino mass model with the asymmetric Yukawa structure

Direct <math><mrow><mi>C</mi><mi>P</mi></mrow></math> asymmetries (<math><msub><mi>A</mi><mrow><mi>C</mi><mi>P</mi></mrow></msub></math>) in the inclusive decays of <math><mover><mi>B</mi><mo>¯</mo></mover><mo>→</mo><msub><mi>X</mi><mi>s</mi></msub><mi>γ</mi></math> and <math><mover><mi>B</mi><mo>¯</mo></mover><mo>→</mo><msub><mi>X</mi><mrow><mi>s</mi><mo>+</mo><mi>d</mi></mrow></msub><mi>γ</mi></math> of the order of 1% will be probed at the BELLE II experiment. In this work, three such asymmetries are studied in the context of a three-Higgs-doublet model (3HDM), and it is shown that all three <math><msub><mi>A</mi><mrow><mi>C</mi><mi>P</mi></mrow></msub></math> can be as large as the current experimental limits. Of particular interest is the <math><msub><mi>A</mi><mrow><mi>C</mi><mi>P</mi></mrow></msub></math> for <math><mover><mi>B</mi><mo>¯</mo></mover><mo>→</mo><msub><mi>X</mi><mrow><mi>s</mi><mo>+</mo><mi>d</mi></mrow></msub><mi>γ</mi></math>, which is predicted to be effectively zero in the Standard Model (SM). A measurement of 2.5% or more for this observable with the full BELLE II data would give <math><mn>5</mn><mi>σ</mi></math> evidence for physics beyond the SM. We display parameter space in the 3HDM for which such a clear signal is possible.

United Kingdom

A. G. Akeroyd

Stefano Moretti

Muyuan Song

<math><mi>C</mi><mi>P</mi></math> asymmetries of <math><mover><mi>B</mi><mo>¯</mo></mover><mo>→</mo><msub><mi>X</mi><mi>s</mi></msub><mo>/</mo><msub><mi>X</mi><mi>d</mi></msub><mi>γ</mi></math> in models with three Higgs doublets

We investigate electric dipole moments (EDMs) in a <math><mi>C</mi><mi>P</mi></math>-violating minimal supersymmetric standard model with the binolike neutralino dark matter (DM) annihilating through the heavy Higgs funnel. Motivated by the current experimental results, in particular, the measured mass of the standard model-like Higgs boson, we consider a mass spectrum with stop masses of about 10 TeV. For the other sfermions, we consider masses of about 100 TeV. We show that <math><mi>C</mi><mi>P</mi></math>-violating phases of the order of ten degrees in gaugino and Higgsino mass parameters are consistent with the current bound by EDMs of the electron, the neutron, and the mercury. They are within the reach of future experiments. We also show that effects of <math><mi>C</mi><mi>P</mi></math>-violating phases induce a difference in DM-nucleon scattering cross section by a factor.

Tomohiro Abe

Naoya Omoto

Electric dipole moments and dark matter in a <math><mi>C</mi><mi>P</mi></math> violating MSSM

We propose a simple model to explain neutrino mass, dark matter and baryogenesis based on the extended Higgs sector which appears in the low-energy effective theory of a supersymmetric gauge theory with confinement. We here consider the SU(2)H gauge symmetry with three flavours of fundamental representations which are charged under the standard SU(3)C×SU(2)L×U(1)Y symmetry and a new discrete Z2 symmetry. We also introduce a Z2 -odd right-handed neutrino superfield in addition to the standard model matter superfields. The low-energy effective theory below the confinement scale contains the Higgs sector with fifteen composite superfields, some of which are Z2 -odd. When the confinement scale is of the order of ten TeV, electroweak phase transition can be sufficiently of first order, which is required for successful electroweak baryogenesis. The lightest Z2 -odd particle can be a new candidate for dark matter, in addition to the lightest R -parity odd particle. Neutrino masses and mixings can be explained by the quantum effects of Z2 -odd fields via the one-loop and three-loop diagrams. We find a benchmark scenario of the model, where all the constraints from the current neutrino, dark matter, lepton flavour violation and LHC data are satisfied. Predictions of the model are shortly discussed.