입자물리학계는 2021년 3월과 4월에 아주 특별한 시기를 맞고 있다. 표준모형을 넘어서는 새로운 입자 물리학의 가능성을 제시하는 두 가지 측정이 발표되었던 것이다. 하나는 CERN의 LHCb 실험그룹에서 발표한 B입자의 붕괴 과정에서 나타난 Lepton Flavor Violation 증거이고, 다른 하나는 Fermilab의 g-2 실험그룹에서 발표한 뮤온의 anomalous magnetic moment 값이다. 두 실험 결과 모두 뮤온 입자와 관련되어 있으며, 표준모형의 예측치에서 3~4 시그마 벗어나 있다. 이에 국내 실험 그룹과 이론 그룹이 참여하여 이실험 결과의 의미를 토의하고, 이를 설명할 수 있는 새로운 물리이론에 대한 고찰 및 실험적 검증 방법을 탐색하고자 한다.
In this talk, I will discuss a few gauge extensions of the SM where one can accommodate the muon g-2 and/or B anomalies.
We propose an extension of the Standard Model (SM) for radiative neutrino mass by introducing a dark U(1) gauge symmetry. We show that the tiny neutrino mass and dark matter candidates are naturally accommodated. Motivated by the recent measurement of muon (g−2) indicating 4.2 deviation from the SM prediction, we examine how this deviation can be explained in this model.
The type-X 2HDM is known to explain the long-standing muon g-2 anomaly due to the presence of a light CP-odd Higgs boson which becomes leptophilic at large tanbeta. The model can be extended with an even lighter singlet boson contributing to the muon g-2. We discuss the current experimental limits on the model and the discovery potential of the extra (Higgs) bosons at lepton and proton colliders.
The recent Fermilab measurement of the muon anomalous magnetic moment yields about 4.2 sigma deviation from the SM prediction. In the Type-X two Higgs doublet model with the Higgs alignment, we study the consequence of imposing the observed muon g-2, along with the theoretical stabilities, electroweak oblique parameters, Higgs precision data, and direct searches at the LEP and LHC. We found that the constraints are very strong, restricting other new scalar boson masses below about 300 GeV. We also show that the observed electron anomalous magnetic moment is consistent with the model prediction and the associated production of a pseudoscalar boson and CP-even scalar boon at the LHC has a high potential to probe the whole surviving parameter space.
We entertain the option of scalar leptoquarks to explain the anomalies in the semi-leptonic decays of B-mesons and the discrepancies in the lepton (g−2)l's including the recent results at Fermilab E989. The RK(∗) and RD(∗) anomalies can be accommodated by the specific couplings for triplet and singlet leptoquarks, respectively, subject to the bounds from B→Kνν¯. We discuss the correlation between the leptonic signatures from leptoquarks such as μ→eγ and the electric dipole moment of electron and show that desirable neutrino masses can be generated dominantly by top-quark loops in the extension of the model with several doublet leptoquarks.
Recently reported anomalies in various B meson decays and also in the anomalous magnetic moment of muon (g − 2) motivate us to consider a particular extension of the standard model incorporating new interactions in lepton and quark sectors simultaneously. Our minimal choice would be leptoquark. In particular, we take vector leptoquark (U1) and comprehensively study all related observables.