National Center for Theoretical science

Hsinchu, Taiwan

National Center for Theoretical science

Hsinchu, Taiwan
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Asaka T.,Niigata University | Ishida H.,National Center for Theoretical science
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2016

Heavy Majorana neutrinos are predicted in addition to ordinary active neutrinos in the models with the seesaw mechanism. We investigate the lepton number violation (LNV) in B decays induced by such a heavy neutrino N with GeV-scale mass. Especially, we consider the decay channel B+→μ+N→μ+μ+π− and derive the sensitivity limits on the mixing angle Θμ by the future search experiments at Belle II and in e+e− collisions at the Future Circular Collider (FCC-ee). © 2016 The Author(s)


Okada H.,National Center for Theoretical science
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2016

We propose a radiatively induced quark and lepton mass model in the first and second generation with extra U(1) gauge symmetry and vector-like fermions. Then we analyze the allowed regions which simultaneously satisfy the FCNCs for the quark sector, LFVs including μ–e conversion, the quark mass and mixing, and the lepton mass and mixing. Also we estimate the typical value for the (g−2)μ in our model. © 2016 The Author(s)


Okada H.,National Center for Theoretical science
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2016

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 allowed region of several physical values in our model. © 2016 The Authors.


Okada H.,National Center for Theoretical science
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2016

We propose a generalized Zee-Babu model with a global U(1) B-L symmetry, in which we classify the model in terms of the number of the hypercharge N/2 of the isospin doublet exotic charged fermions. Corresponding to each of the number of N, we need to introduce some multiply charged bosons in order to make the exotic fields decay into the standard model fields. We also discuss the muon anomalous magnetic moment and the diphoton excess depending on N, and we show what kind of models are in favor of these phenomenologies. © 2016 The Authors.


Okada H.,National Center for Theoretical science | Yagyu K.,University of Southampton
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2016

We discuss a possibility to explain the 750 GeV diphoton excess observed at the LHC in a three-loop neutrino mass model which has a similar structure to the model by Krauss, Nasri and Trodden. Tiny neutrino masses are naturally generated by the loop effect of new particles with their couplings and masses to be of order 0.1-1 and TeV, respectively. The lightest right-handed neutrino, which runs in the three-loop diagram, can be a dark matter candidate. In addition, the deviation in the measured value of the muon anomalous magnetic moment from its prediction in the standard model can be compensated by one-loop diagrams with exotic multi-charged leptons and scalar bosons. For the diphoton event, an additional isospin singlet real scalar field plays the role to explain the excess by taking its mass of 750 GeV, where it is produced from the gluon fusion production via the mixing with the standard model like Higgs boson. We find that the cross section of the diphoton process can be obtained to be a few fb level by taking the masses of new charged particles to be about 375 GeV and related coupling constants to be order 1. © 2016 The Authors.


Huang W.-C.,TU Dortmund | Tsai Y.-L.S.,University of Tokyo | Yuan T.-C.,Academia Sinica, Taiwan | Yuan T.-C.,National Center for Theoretical science
Nuclear Physics B | Year: 2016

In light of the recent 750 GeV diphoton anomaly observed at the LHC, we study the possibility of accommodating the deviation from the standard model prediction based on the recently proposed Gauged Two Higgs Doublet Model. The model embeds two Higgs doublets into a doublet of a non-abelian gauge group SU(2)H, while the standard model SU(2)L right-handed fermion singlets are paired up with new heavy fermions to form SU(2)H doublets, and SU(2)L left-handed fermion doublets are singlets under SU(2)H. An SU(2)H scalar doublet, which provides masses to the new heavy fermions as well as the SU(2)H gauge bosons, can be produced via gluon fusion and subsequently decays into two photons with the new fermions circulating the triangle loops to account for the deviation from the standard model prediction. © 2016 The Authors.


Chang W.-F.,National Tsing Hua University | Ng J.N.,TRIUMF Laboratory Particle and Nuclear Physics | Wu J.M.S.,National Center for Theoretical science
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2012

We study the implications the recent results from the LHC Higgs searches have on scalar new physics. We study the impact on both the Higgs production and decay from scalars with and without color, and in cases where decoupling does and does not happen. We investigate possible constraints on scalar parameters from the production rate in the diphoton channel, and also the two vector boson channels. Measurements from both channels can help disentangle new physics due to color from that due to charge, and thus reveal the nature of the new scalar states. © 2012 American Physical Society.


Tang Y.,National Center for Theoretical science
Journal of High Energy Physics | Year: 2012

With the latest LHC available results, we consider the generic constraints on massive graviton. Both dijet and dilepton resonance searches are used. The limits on parameter space can be applied to many models. As an illustration, we show the constraints for Randall-Sundrum (RS) model. Implications on massive graviton and the coupling strength are discussed. For k/M pl = 0.1, M G < 2.2 TeV region is excluded at 95% confidence level. We also present some interesting implications on the RS radion with respect to the 125 GeV excess at the LHC. For k/M pl = 0.1, Λ φ < 13.8TeV is excluded where Λ φ is the scale to charactarize the interaction strengh of radion. © 2012 SISSA.


Chen C.-S.,National Center for Theoretical science | Tang Y.,National Center for Theoretical science
Journal of High Energy Physics | Year: 2012

Motivated by the discovery hint of the Standard Model (SM) Higgs mass around 125GeV at the LHC, we study the vacuum stability and perturbativity bounds on Higgs scalar of the SM extensions including neutrinos and dark matter (DM). Guided by the SM gauge symmetry and the minimal changes in the SM Higgs potential we consider two extensions of neutrino sector (Type-I and Type-III seesaw mechanisms) and DM sector (a real scalar singlet (darkon) and minimal dark matter (MDM)) respectively. The darkon contributes positively to the ? function of the Higgs quartic coupling ? and can stabilize the SM vacuum up to high scale. Similar to the top quark in the SM we find the cause of instability is sensitive to the size of new Yukawa couplings between heavy neutrinos and Higgs boson, namely, the scale of seesaw mechanism. MDM and Type-III seesaw fermion triplet, two nontrivial representations of SU(2)L group, will bring the additional positive contributions to the gauge coupling g2 renormalization group (RG) evolution and would also help to stabilize the electroweak vacuum up to high scale. © 2012 SISSA.


Furuuchi K.,Manipal University India | Wu J.M.S.,National Center for Theoretical science
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2014

The interrelation between inflationary cosmology and new physics beyond the Standard Model (SM) is studied in a U(1)B-L extension of the SM embedded in a (4+1)-dimensional spacetime. In the scenario we study, the inflaton arises from the Wilson loop of the U(1)B-L gauge group winding an extra-dimensional cycle. Particular attention is paid to the coupling between the inflaton and SM particles that are confined on a brane localized in the extra dimension. We find that the inflaton decay channels are rather restricted in this scenario and the resulting reheating temperature is relatively low. © 2013 The Authors.

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