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Minimal flavored U(1)′ for B -meson anomalies
Bian, Ligong,Choi, Soo-Min,Kang, Yoo-Jin,Lee, Hyun Min American Physical Society 2017 Physical Review D Vol.96 No.7
<P>We consider an anomaly free U(1)' model with favorable couplings to heavy flavors in the Standard Model ( SM), as motivated by B- meson anomalies at LHCb. Taking the U(1)' charge to be Q' = y(L mu - L tau) + x(B-3 - L-3), we can explain theB- meson anomalies without invoking extra charged fermions or flavor violation beyond the SM. We showthat there is a viable parameter space with a small x that is compatible with other meson decays, tau lepton, and neutrino experiments as well as theLHCdimuon searches. We briefly discuss the prospects of discovering the Z' gauge boson at the LHC in the proposed model.</P>
CP violation effects in the diphoton spectrum of heavy scalars
Bian, Ligong,Chen, Ning,Zhang, Yongchao American Physical Society 2017 Physical Review D Vol.96 No.9
<P>In a class of new physics models, an extended Higgs sector and new CP-violating sources are simultaneously present in order to explain the baryon asymmetry in the Universe. The aim of this work is to study the implications of beyond the Standard Model (SM) CP violation for the searches of heavy scalars at the LHC. In particular, we focus on the diphoton channel searches in the CP-violating two-Higgs-doublet model (CPV 2HDM). To have a sizable CPV in the scalar sector, the two heavy neutral scalars in 2HDM tend to be nearly degenerate. The theoretical constraints of unitarity, perturbativity and vacuum stability are considered, which requires that the heavy scalars M-H less than or similar to 1 TeV in a large region of the parameter space. The experimental limits are also taken into account, including the direct searches for heavy neutral scalars in the final state of the SM h, W and Z bosons; the differential (tt) over bar data; those from the charged scalar sector which is implied by the oblique T parameter; and the precise measurements of the electric dipole moments of electrons and mercury. The quantum interference effects between the resonances and the SM background are crucially important for the diphoton signals, and the CPV mixing of the quasidegenerate heavy scalars could enhance significantly the resonance peak. With an integrated luminosity of 3000 fb(-1) at the LHC, almost the whole parameter space of CPV 2HDM could be probed in the diphoton channel, and the CPV could also be directly detected via the diphoton spectrum.</P>
Future prospects of mass-degenerate Higgs bosons in the CP -conserving two-Higgs-doublet model
Bian, Ligong,Chen, Ning,Su, Wei,Wu, Yongcheng,Zhang, Yu American Physical Society 2018 Physical Review D Vol.97 No.11
<P>The scenario of two mass-degenerate Higgs bosons within the general two-Higgs-doublet model (2HDM) is revisited. We focus on the global picture when two CP-even Higgs bosons of h and H are nearly mass-degenerate. A global fit to the signal strength of the 125 GeV Higgs measured at the LHC is performed. Based on the best-fit result of the 2HDM mixing angles (alpha, beta), theoretical constraints, charged and CP-odd Higgs boson direct search constraints and the electroweak precision constraints are imposed to the 2HDM parameter space. We present the signal predictions of the (4b, 2b2 gamma) channels for the benchmark models at the LHC 14 TeV runs. We also study the direct Higgs boson pair productions at the LHC, and the Z-associated Higgs boson pair production search at the ILC 500 GeV runs, as well as the indirect probes at the CEPC 250 GeV run. We find that the massdegenerate Higgs boson scenario in the Type-II 2HDM can be fully probed by these future experimental searches.</P>
Flavor and CP-violating Higgs sector in two Higgs doublet models with U(1)'
Bian Ligong,Lee Hyun Min,Park Chan Beom 한국물리학회 2021 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.79 No.2
We investigate the role of a local U(1)' symmetry for the problem of CP violation in the effective theory for two Higgs doublet models and its microscopic counterparts. First, in the two Higgs doublet models with U(1)' , we show that the higherdimensional operators in the scalar potential violate the CP symmetry with an interplay with the mixing mass parameter, giving rise to small mixings between CP-even and CP-odd scalars. Motivated by the B-meson anomalies in recent years, we take the flavored U(1)' to be a benchmark model for specifying the flavor structure. Then, we calculate the electric dipole moment of the electron (eEDM) at two loops due to the CP-violating higher-dimensional operators and identify the correlation between the masses of heavy Higgs bosons and the cutoff scale from the bound on the eEDM. We also comment on the possibility of making an independent test of the CP violation in collider searches for heavy Higgs bosons. Finally, we show how the obtained eEDM results in the effective theory can be used to constrain microscopic models with an explicit CP violation in partially decoupled or dark sectors.