Studying Structure of Electroweak Corrections

Several different effects in electroweak quantum corrections are explored separately through the latest data on the weak-boson masses. The leading-log approximation, the improved-Born approximation and the non-decoupling top-quark effects are studied without depending on the recent CDF data of $m_t$, and the results are given in a form independent of the Higgs mass. On the other hand, the bosonic- and the non-decoupling Higgs effects are examined by fully taking account of those CDF data. It is emphasized that future precision measurements of $M_W$ and $m_t$ are considerably significant not only for further studies of the electroweak theory at higher confidence level but also for new physics searches beyond it.Comment: 18 page

Non-trivial Test of Electroweak Quantum Effects

Based on recent $W$-mass measurements, the electroweak theory is tested at non-trivial quantum correction level, i.e., beyond the Born approximation with $\alpha(M_Z)$ instead of $\alpha$. We can conclude that some non-Born type corrections must exist at more than 92 % confidence level, and the non-decoupling top-quark corrections are required at 97 % confidence level.Comment: 7 page

Studying possible CP-violating Higgs couplings through top-quark pair productions at muon colliders

We study possible anomalous CP-violating Higgs couplings to mu mu-bar and t t-bar fully model-independent way through top-quark pair productions at muon colliders. Assuming additional non-standard neutral Higgs bosons, whose couplings with top-quark and muon are expressed in the most general covariant form, we carry out analyses of effects which they are expected to produce via CP-violating asymmetries and also the optimal-observable (OO) procedure under longitudinal and transverse muon polarizations. We find the measurement of the asymmetry for longitudinal beam polarization could be useful to catch some signal of CP violation, and an OO analysis might also be useful if we could reduce the number of unknown parameters with a help of other experiments and if the size of the parameters is at least O(1) ~ O(10).Comment: Final version (to appear in JHEP

Top-quark pair productions and CP-violating Higgs interactions at muon colliders

We study CP-violation effects from possible non-standard Higgs interactions in beyond-the-standard-model physics through top-quark pair productions at μμ⁻ colliders. We calculate two CP-violating asymmetries for longitudinal and transverse beam polarizations, and study their dependence on √s and mH, the additional Higgs mass. Judging from their computed absolute values, we conclude that there are more chances to find non-standard effects in analyses using AL, the longitudinal asymmetry, than in those using AT, the transverse asymmetry

Decoupling of Anomalous Top-Quark-Decay Vertices in Angular Distribution of Secondary Particles

Angular distribution of a secondary particle from top-quark decays is studied in a simple and general manner, paying careful attention to how relevant the top-quark production mechanism is. The conditions that lead to the distribution free from any possible anomalous top-quark decay interactions are specified. It is discussed how important the approximations adopted in earlier papers are.Comment: 9 pages, Latex, Final version (to appear in Phys.Lett. B

Addendum to: Search for anomalous top-gluon couplings at LHC revisited

In our latest paper "Search for anomalous top-gluon couplings at LHC revisited" in Eur. Phys. J. C65 (2010), 127-135 (arXiv:0910.3049 [hep-ph]), we studied possible effects of nonstandard top-gluon couplings through the chromoelectric and chromomagnetic moments of the top quark using the total cross section of ppbar/pp --> ttbar X at Tevatron/LHC. There we pointed out that LHC data could give a stronger constraint on those two parameters, which would be hard to obtain from Tevatron data alone. We show here the first CMS measurement of this cross section actually makes it possible.Comment: 5 pages, 1 figure, LaTeX2e, Final version (to appear in Eur. Phys. C

Optimal-observable Analysis of Possible Non-standard Top-quark Couplings in pp -> t t-bar X -> l^+ X'

Possible non-standard top-quark interactions with the gluon and the W boson induced by SU(3) X SU(2) X U(1) gauge-invariant dimension-6 effective operators are studied for hadron-collider experiments. Current limits on top-gluon couplings are presented by using the latest experimental data of t t-bar productions at the Tevatron and the Large Hadron Collider (LHC). The optimal-observable procedure is applied to the charged-lepton distributions in p p -> t t-bar X -> l^+ X' (l = e or mu) at the LHC in order to estimate the expected statistical uncertainties in measurements of those non-standard top-gluon and top-W couplings that contribute to this process in the leading order.Comment: 16 pages, 1 figure, Discussion of stabilities in estimating statistical errors and related one reference added. Final version (to appear in Phys. Lett. B