Research Interest

Research Brief The Standard Model (SM) for particle physics had been tested very precisely. Recently, July 2012, an observation of the Higgs boson, the last particle in the SM, was reported at the CERN LHC in Geneva. Taking a year, the particle is confirmed as "a" Higgs boson. However, the interactions of the Higgs boson have not been established yet. On the other hand, there are phenomena which must be explained by the new physics beyond the SM (BSM). To understand and to test the BSM phenomena, I am focusing on the Higgs physics.

Keywords Higgs boson, Extended Higgs Sector, Electroweak Symmetry Breaking, Collider (LHC, ILC) Phenomenology, Tau Lepton, Neutrino Mass, Flavor Physics, Dark Matter, Axion

Brief Introduction of My Works

Scalar multiplet and Landau pole [ Particle Physics Medal, Young Scientist Award in Theoretical Particle Physics (Japan): with Dr. Yuta Hamada and Mr. Kiyoharu Kawana (Kyoto Univ.) ]
Phys. Lett. B747 (2015) 238 hep-ph/1505.01721
The renormalization group running effects on the new scalar quartic coupling constants are evaluated. Even if the scalar quartic coupling constants are zeros at a certain scale, the coupling constants are induced by the one-loop effect of the weak gauge bosons. Once non-vanishing couplings are generated, the couplings rapidly increase by renormalization group effect of the quartic coupling constant itself. As a result, a lower cutoff scale is indicated due to the appearance of the Landau pole.

Unitarity and Finiteness of Oblique Corrections Phys. Rev. D91, 034030 (2015) hep-ph/1409.1709
It is known that unitarity of the weak boson scattering at high energy is violated if the Higgs coupling deviates from the SM predictions. Therefore, sum-rules of the Higgs couplings and of the extra Higgs coupling are obtained in order to guarantee the unitarity. Constraints on the extra Higgs bosons are studied using the observed Higgs boson data through these sum-rules. We also show a relation between the unitarity and finiteness of the oblique parameters if the model only contains neutral Higgs bosons. In this case, a stronger constraint on the extra Higgs bosons is obtained from the electroweak precision tests.

Fingerprinting Non-minimal Higgs sector Phys. Rev. D90, 075001 (2014) hep-ph/1406.3294
It has been shown that the discovered Higgs boson is close to the Higgs boson in the Standard Model (SM). On the other hand, additional Higgs bosons are oftern predicted in the new physics beyond the SM. Using the precisely measured valule of the Higgs boson coupling, the property of the extended Higgs sector can be probed by the Higgs coupling deviation perturns from the SM predictions. The direct search of the 2nd Higgs boson at the LHC has also discussed.

Higgs Septet Model Phys. Rev. D87, 053004 (2013) hep-ph/1301.6455
The SU(2) representaion of the Higgs boson is strongly constrained by the electroweak ρ paramter. In the Standard Model, a Higgs field is chosen as a doublet, which gives ρ=1 at leading order. The next minimal representaion, which predicts ρ=1, is a 7-plet (septet). However, there is a probrem (prediction of a massless particle). We have extended the model without such a problem and with a Dark Matter candidate. A typical prediction of the septet Higgs is enhanced Gauge-Gauge-Higgs coupling, which is a smoking gun at the LHC.

Lepton Number Violation at the LHC Phys. Lett. B718 (2013) 1436 hep-ph/1210.5622
A lepton number violation (LNV) has not been discovered, but it is possibe in new physics models. In usual, a LNV search use the macroscopic amount of materials in low energy experiments in order to enhance reaction rates. Collider beams cannot hundle such a number of materials, however, the process can be enhanced by focusing on the particle decay in the acroscopic time. We have shown a model for radiative neutrino mass via the scalar leptoquarks and diquarks, which provides an observable LNV signature at the LHC.

Discrimination of Doubly Charged Higgs Bosons at the LHC [ Particle Physics Medal, Young Scientist Award in Theoretical Particle Physics (Japan): with Dr. Hiroaki Sugiyama (Maskawa Inst.) and Dr. Hiroshi Yokoya (Univ. of Toyama) ]
Phys. Lett. B717 (2012) 229 hep-ph/1207.0179
The doubly charged Higgs boson is often introduced in models for neutrino mass generation and others. Discrimination of such particles is important to understand the mass generation mechanism for neutrinos. The doubly charged Higgs bosons interact with a pair of left- or right-handed leptons. On the other hand, the chirality of the (boosted) tau leptons can be distinguished by looking the kinematical distribution of its decay products. Therefore, the property of the parent doubly charged Higgs boson can be determined by extracting the decay through the tau leptons.