Next-to-leading order QCD effect of $W'$ on top quark Forward-Backward Asymmetry

Physical review D: Particles and fields 10/2011; DOI: 10.1103/PhysRevD.85.034020
Source: arXiv

ABSTRACT We present the calculations of the complete next-to-leading order (NLO) QCD
corrections to the total cross section, invariant mass distribution and the
forward-backward asymmetry ($\rm A_{FB}$) of top quark pair production mediated
by $W'$ boson. Our results show that in the best fit point in the parameter
space allowed by data at the Tevatron, the NLO corrections change the new
physics contributions to the total cross section slightly, but increase the
$\rm A_{FB}$ in the large invariant mass region by about 9%. Moreover, we
evaluate the total cross section and charge asymmetry ($\rm{A}_{\rm{C}}$) of
top pair production at the LHC, and find that both total cross section and
$A_{\rm C}$ can be used to distinguish NP from SM with the integrated
luminosity increasing.

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    ABSTRACT: The excess of top quark forward-backward asymmetry ($A^t_{FB}$) reported by the Tevatron and the enhancement of the Higgs decay to diphoton observed by the LHC may point to a same origin of new physics. In this note we examined such anomalies in the two-Higgs-doublet model with a color-triplet scalar. We found that under current experimental constraints this model can simultaneously explain both anomalies at $1\sigma$ level. Also, we examined the Higgs decay $h\to Z\gamma$ and displayed its correlation with $h\to \gamma\gamma$. We found that unlike other models, this model predicts a special correlation between $h\to Z\gamma$ and $h\to \gamma\gamma$, i.e., the $Z\gamma$ rate is highly suppressed while the $\gamma\gamma$ rate is enhanced. This behavior may help to distinguish this model in the future high luminosity run of the LHC.
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    ABSTRACT: We study the renormalization group(RG) evolution of four-quark operators that contribute to the top pair production. In particular, we focus on the cases in which certain observables are first induced from the one-loop RG while being absent at tree-level. From the operator mixing pattern, we classify all such RG-induced phenomena and underlying models that can induce them. We then calculate the full one-loop QCD RG evolution as the leading estimator of the effects and address the question of which RG-induced phenomena have largest and observable effects. The answer is related to the color structure of QCD. The studied topics include the RG-induction of top asymmetries, polarizations and polarization mixings as well as issues arising at this order. The RG-induction of top asymmetries is further compared with the generation of asymmetries from QCD and QED at one-loop order. We finally discuss the validity of using the RG as the proxy of one-loop effects on the top pair production. As an aside, we clarify the often-studied relations between top pair observables.
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    ABSTRACT: We study the connection between the same sign top (SST) and the top quark forward-backward asymmetry $A^t_{FB}$. We find that a large class of new physics models that have been proposed to account for the $A^t_{FB}$ lead to SST quark production rate much larger than the observed rate at the LHC and consequently are severely constrained or ruled out. Our model independent, general, operator analysis shows that none of the tree-level flavor-changing operators are able to explain $A^t_{FB}$ and simultaneously remain consistent with the same-sign top-quark production constraints from the LHC data.
    Journal of High Energy Physics 01/2013; 2013(4). DOI:10.1007/JHEP04(2013)035 · 6.22 Impact Factor

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