Pohang University of Science and Technology · Physics and Astronomy
Professor Hiroshi Okada's research lab specializes in flavor physics and beyond-Standard Model particle physics, focusing on the theoretical unification of quark and lepton masses and mixings through discrete non-Abelian flavor symmetries such as $A_4$ and $S_3$. The lab investigates modular forms and modular symmetries to construct realistic flavor models, particularly in the context of neutrino mass generation, leptonic CP violation, and radiative seesaw mechanisms. Current research also explores dark matter candidates, lepton flavor violation, and collider phenomenology, especially in connection with the Large Hadron Collider and cosmological data such as WMAP/Planck results.
Figures are computed from collected data and may differ slightly.
We discuss the quark mass matrices in the $A_4$ modular symmetry, where the $A_4$ triplet of Higgs is introduced for each up-quark and down-quark sectors, respectively. The model has six real parameters and two complex parameters in addition to the modulus $\tau$. By inputting six quark masses and three CKM mixing angles, we can predict the CP violation phase $\delta$ and the Jarlskog invariant $J_{CP}$. The predicted ranges of $\delta$ and $J_{CP}$ are consistent with the observed values. The a
We propose a one-loop induced radiative seesaw model applying a modular ${S}_{3}$ flavor symmetry, which is known as the minimal non-Abelian discrete group. In this scenario, dark matter (DM) candidate is correlated with neutrinos and lepton flavor violations (LFVs). We show several predictions of mixings and phases satisfying LFVs, observed relic density, and neutrino oscillation data.
Abstract We study quark and lepton mass matrices in the $$A_4$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>A</mml:mi> <mml:mn>4</mml:mn> </mml:msub> </mml:math> modular symmetry towards the unification of the quark and lepton flavors. We adopt modular forms of weights 2 and 6 for quarks and charged leptons, while we use modular forms of weight 4 for the neutrino mass matrix which is generated by the Weinberg operator. We obtain the successful quark mass matrices
We propose a radiative seesaw model with an inert triplet scalar field in which Majorana neutrino masses are generated at the two-loop level. There are fermionic or bosonic dark matter candidates in the model. We find that each candidate can satisfy the WMAP data when its mass is taken to be around the half of the mass of the standard model like Higgs boson. We also discuss phenomenology of the inert triplet scalar bosons, especially focusing on the doubly-charged scalar bosons at Large Hadron C
In the modular invariant flavor model of ${\mathrm{A}}_{4}$, we study the hierarchical structure of lepton/quark flavors at nearby fixed points of $\ensuremath{\tau}=i$ and $\ensuremath{\tau}=\ensuremath{\omega}$ of the modulus, which are in the fundamental domain of $\mathrm{PSL}(2,\mathbb{Z})$. These fixed points correspond to the residual symmetries ${\mathbb{Z}}_{2}^{S}={I,S}$ and ${\mathbb{Z}}_{3}^{ST}={I,ST,(ST{)}^{2}}$ of ${\mathrm{A}}_{4}$, where $S$ and $T$ are generators of the ${A}_{4
We propose a radiative seesaw model based on a modular A4 symmetry, which has good predictability in the lepton sector. We execute a numerical analysis to search for parameters that satisfy the experimental constraints such as those from neutrino oscillation data and lepton flavor violations. Then, we present several predictions in our model that originate from the modular symmetry at a fixed point as well as fundamental region of τ.
We study the neutrino sector in a minimal $SU(3{)}_{L}\ifmmode\times\else\texttimes\fi{}U(1{)}_{X}$ model, in which its mass is generated at a one-loop level with the charged lepton mass, and hence, there exists a strong correlation between the charged-lepton mass and the neutrino mass. We identify the parameter region of this model to satisfy the current neutrino oscillation data as well as the constraints on lepton flavor violating processes. We also discuss a possibility to explain the muon a
We construct a radiative inverse seesaw model with local $B\ensuremath{-}L$ symmetry, and investigate the flavor structure of the lepton sector and the fermionic dark matter. Neutrino masses are radiatively generated through a kind of inverse seesaw framework. The Pontecorvo-Maki-Nakagawa-Sakata matrix is derived from each mixing matrix of the neutrino and charged lepton sector with a large Dirac $CP$ phase. We show that the annihilation processes via the interactions with Higgses, which are ind
We propose a two-loop induced Zee-Babu-type neutrino mass model at the TeV scale. Although there is no dark matter candidate in the original Zee-Babu model, our model can include the dark matter by introducing an unbroken discrete ${Z}_{2}$ symmetry. The discrepancy between the experimental value of the muon anomalous magnetic moment (muon $g\ensuremath{-}2$) and its prediction in the standard model can be explained by contributions from additional vectorlike charged leptons which are necessary
We propose a new mechanism where both Dirac masses for the charged leptons and Majorana masses for neutrinos are generated via quantum levels. The charged-lepton masses are given by the vacuum expectation values (VEVs) of the Higgs doublet field and that of a triplet field. On the other hand, neutrino masses are generated by two VEVs of triplet Higgs fields. As a result, the hierarchy between the masses for charged leptons and neutrinos can be explained by the triplet VEVs which have to be much
We propose a four-loop induced radiative neutrino mass model inspired by the diphoton excess at 750 GeV recently reported by ATLAS and CMS, in which a sizable diphoton excess is obtained via photon fusion introducing multi doubly-charged scalar bosons. Also we discuss the muon anomalous magnetic moment, and a dark matter candidate. The main process to explain the observed relic density relies on the final state of the new particle at 750 GeV. Finally we show the numerical results and obtain allo
We revisit our previous model proposed by Okada and Yagyu [Phys. Rev. D 89, 053008 (2014)], in which lepton masses, except the tauon mass, are generated at the one-loop level in TeV-scale physics. Although in the previous work, rather large Yukawa coupling constants, i.e., greater than about 3, are required to reproduce the muon mass, we do not need to introduce such large $\mathcal{O}(1)$ couplings. In our model, masses for neutrinos (charged leptons) are generated by higher-dimensional operato
We study quark and lepton mass matrices in the $A_4$ modular symmetry towards the unification of the quark and lepton flavors. We adopt modular forms of weights $2$ and $6$ for quarks and charged leptons, while we use modular forms of weight $4$ for the neutrino mass matrix which is generated by the Weinberg operator. We obtain the successful quark mass matrices, in which the down-type quark mass matrix is constructed by modular forms of weight $2$, but the up-type quark mass matrix is construct
We propose a radiative lepton model, in which the charged lepton masses are generated at one-loop level, and the neutrino masses are induced at two-loop level. On the other hand, tau mass is derived at tree level since it is too heavy to generate radiatively. Then we discuss muon anomalous magnetic moment together with the constraint of lepton flavor violation. A large muon magnetic moment is derived due to the vector like charged fermions which are newly added to the standard model. In addition
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