51 research outputs found

    Studying Structure of Electroweak Corrections

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    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 mtm_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 MWM_W and mtm_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

    Decoupling theorem in top productions/decays revisited : To what extent can we understand it visually?

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    I revisit here the decoupling theorem in top-quark productions/decays, which states that the angular distribution of any final-particle produced in those processes does not depend on any possible nonstandard top-quark decay interactions at their leading order when certain conditions are satisfied. Toward a simple, intuitive and visual understanding of this theorem, I will study to what extent we could explain why such a theorem holds without relying on any specific/detailed calculations

    Non-trivial Test of Electroweak Quantum Effects

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    Based on recent WW-mass measurements, the electroweak theory is tested at non-trivial quantum correction level, i.e., beyond the Born approximation with α(MZ)\alpha(M_Z) instead of α\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

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    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

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    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

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

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    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

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

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    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
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