Possible anomalous top-quark couplings induced by SU(2) × U(1) gauge-invariant dimension-6 effective operators were studied in the process of tt productions and decays at polarized γγ colliders. Two CP -violating asymmetries, a linearpolarization asymmetry and a circular-polarization asymmetry, were computed including both non-standard ttγ and γγH couplings. An optimal-observable analysis for the process γγ → tt → ℓ ± · · · was performed in order to estimate the precision for determination of all relevant non-standard couplings, including the anomalous tbW coupling.

Through top-quark pair productions at LHC, we study possible effects of nonstandard top-gluon couplings yielded by SU(3)×SU(2)×U(1) invariant dimension-6 effective operators. We calculate the total cross section and also some distributions for pp → ttX as functions of two anomalous-coupling parameters, i.e., the chromoelectric and chromomagnetic moments of the top, which are constrained by the total cross section σ(pp → ttX) measured at Tevatron. We find that LHC might give us some chances to observe sizable effects induced by those new couplings. ♯1 Here (and hereafter) we do not show the color-component indices of u/v spinors, and also all the spin variables for simplicity.

Constraints on the nonstandard top-gluon couplings composed of the chromomagnetic-and chromoelectric-dipole moments of the top quark are updated by combining the latest data of top-pair productions from the Tevatron, 7-TeV LHC, and 8-TeV LHC. We find that adding the recent 8-TeV data to the analysis is effective to get a stronger constraint on the chromoelectric-dipole moment than the one from the Tevatron and 7-TeV LHC alone. We also discuss how those constraints on the nonstandard couplings could be further improved when the 14-TeV LHC results become available in the near future.

We study momentum distributions of the final-state charged lepton in p p=pp ! t t ! ' þ Xð' ¼ e or "Þ at hadron colliders, i.e., Tevatron and Large Hadron Collider (LHC), in order to explore possible newphysics effects in the top-quark sector. Assuming general model-independent t tg þ t tgg and tbW interactions beyond the standard model, we first derive analytical formulas for the corresponding parton-parton processes. We then compute the lepton angular, energy, and transverse-momentum distributions in p p=pp collisions to clarify how they are affected by those anomalous couplings.

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