Constraints on unparticle physics from the $gt\bar t$ anomalous coupling

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Abstract

We study the impact of unparticle physics to the chromomagnetic dipole moment (CMDM) of the top quark. We compute the effect induced by unparticle operators of scalar and vector nature coupled to fermions on the CMDM. We find that this dipole moment is sensitive to the scale dimensions $d_u$ of the unparticle and the new couplings of the respective effective operators. Using the bounds imposed on the CMDM by low-energy precision and Tevatron measurements we derive indirect limits on the unparticle parameter space. In particular, we find that the scalar-unparticle operator contribution fulfills both constraints for most of the unparticle parameter space, while the low-energy precision bound on the CMDM excludes a vector-unparticle contribution for low values of respective scale dimension $d_u$.

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Constraining Anomalous Top Quark Couplings at the Tevatron

Tom Rizzo, Alex Kagan, David Atwood (1994)

We explore the influence of an anomalous chromomagnetic moment, $\kappa$, onthe production characteristics of top quark pairs at the Tevatron. We find that for top quarks in the 170 GeV mass range, present searches are probing values of $\kappa$ of order ${1 \over 3}$. For $\kappa$'s in this range we find that significant enhancements in the both the $q \bar q,~gg \to t \bar t$ production cross sections are obtained. Once top has been verified and QCD uncertainties are under control, future high statistics measurements at the Tevatron will eventually be sensitive to values of $\kappa$ with magnitudes smaller than 0.10-0.15. We discuss a class of scalar technicolor models which may produce large values of $\kappa$ in conjunction with generation of $m_t$.

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Dimension-six CP-violating operators of the third-family quarks and their effects at colliders

, (2010)

We listed all possible dimension-six CP-violating $SU_c(3)\times SU_L(2)\times U_Y(1)$ invariant operators involving the third-family quarks, which can be generated by new physics at a higher energy scale. The expressions of these operators after electroweak symmetry breaking and the induced effective couplings $Wt\bar b$, $Xb\bar b$ and $Xt\bar t$ $(X=Z,\gamma,g,H)$ are also presented. We have evaluated sample contributions of these operators to CP-odd asymmetries of transverse polarization of top quark in single top production at the upgraded Tevatron, the similar effect in top-antitop pair production at the NLC, and the CP-odd observables of momentum correlations among the top quark decay products at the NLC. The energy and luminosity sensitivity in probing these CP-violating new physics has also been studied.

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Probing Anomalous Chromomagnetic Top Quark Couplings at the NLC

Thomas G. Rizzo (1994)

The Next Linear Collider(NLC) will provide a excellent tool for probing the detailed nature of the top quark. By extending the recent analysis of Dokshitzer, Khoze and Sterling, we perform a preliminary examination of the influence of an anomalous chromomagnetic moment for the top, $\kappa$, on the spectrum of gluon radiation associated with $t\bar t$ production. In particular, we analyze the sensitivity of future data to non-zero values of $\kappa$ and estimate the limits that can be placed on this parameter at the NLC with center of mass energies $\sqrt {s}=$ 500 and 1000 GeV.