Looking around our Universe, everything is made of matter, not antimatter. Cosmological observations show that our Universe is baryon-asymmetric, which is known as the Baryon Asymmtery of the Universe (BAU). 

No one knows why only matter is left, and this is one of the mysteries in our Universe. 

 

It is called Baryogebesis to solve the BAU in terms of particle physics, and many scenarios have been created till this date. Among them, one attractive scenario is Electroweak Baryogenesis (EWBG), where the BAU can be produced during the electroweak phase transition. Since the energy scale of EWBG is O(100) GeV, it would be possible to verify EWBG by collider physics. Actually, the discovery of the Higgs boson on July 4th, 2012, excluded the Standard Model EWBG.

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Given that the Large Hadron Collider is running now, it is especially ripe for verfication of EWBG. Moreover, not only collider experiments but also precision measurements of Electric Dipole Moment (EDM) such as electron, neutron and proton can also have an important role in verification of EWBG. Because, sufficient CP violation is essential for BAU. 

 

My current research interest is the verifiability for the electroweak baryogenesis by collider experiments through the Higgs physics and EDMs.

 

 

 

 

 

CURRENT WORKS

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Phys. Lett. B762 (2016) 315-320

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Flavor-changing Higgs decay does not appear in the framework of the Standard Model, but there is a possibility that it occurs if new physics exists. Recently, the CMS Collaboration reported the excess in the Higgs decay to muon and tauon, and the central value of the branching ratio is 0.84%. Although it would be shown that the excess becomes less by the latest LHC data, it is still worth considering what kind of new physics might exist behind it. 

On the other hand, in electroweak baryogenesis, CP violation is necessary in a collision between bubble and particle, wherein flavor-changing process is essential for successful baryon asymmetry. Actually, the interaction lead to the flavor-changing Higgs decay at zero temperature.

In this Letter, focusing on not only the excess shown by the CMS but a longstanding anomaly in muon g-2, we examined parameter regions where these two anomalies and baryon asymmetry can successfully be explained in general two-Higgs doublet model. Our results turned out that the parameter region marginally exists, but can be probed by electron EDM in near future.

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Phys. Lett. B755 (2016) 491-497

 

It is discussed that the aspects of CP-violating effects on electroweak baryogensis in the extended Standard Model. Since colored particles are severely constrained by current collider experiments, it is natural to consider scenario where noncolored  particles are newly introduced.  The modle includes both a real singlet and two electroweak-interacting fermions. The former plays a role in achieving the first order electroweak phase transition, and the latter supply a CP phase that is directly related to the BAU.

Since the CP phase can also induce the electron EDM, it is possible to verify the model by it. Actually, since the other BAU-unrelated  CP phase is also present, the verifiability is not so obvious. However, it is found that the signal strength of the Higgs decay to two gammas and other EDMs such as neutron and proton help it.