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

**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:**In order to explain the Tevatron anomaly of the top quark forward-backward asymmetry $A_{FB}^t$ in the left-right twin Higgs model, we choose to give up the lightest neutral particle of $\hat{h}$ field as a stable dark matter candidate. Then a new Yukawa interaction for $\hat{h}$ is allowed, which can be free from the constraint of same-sign top pair production and contribute sizably to $A_{FB}^t$. Considering the constraints from the production rates of the top pair ($t\bar t$), the top decay rates and $t\bar{t}$ invariant mass distribution, we find that this model with such new Yukawa interaction can explain $A_{FB}^t$ measured at the Tevatron while satisfying the charge asymmetry $A_{C}^t$ measured at the LHC.Moreover, this model predicts a strongly correlation between $A_{C}^t$ at the LHC and $A_{FB}^t$ at the Tevatron, i.e., $A_{C}^t$ increases as $A_{FB}^t$ increases. ##### Probing topcolor-assisted technicolor from top charge asymmetry and triple-top production at the LHC

[Show abstract] [Hide abstract]**ABSTRACT:**In a topcolor-assisted technicolor model (TC2) with large FCNC top quark couplings, we study its correlated contributions to the top quark forward-backward asymmetry ($A_{FB}$) at the Tevatron, the top charge asymmetry ($A_{C}$) and the triple-top production at the LHC. Under current constraints on the top quark from the LHC and Tevatron(such as the total and differential production rates), we scan the parameter space of such a TC2 model. We find that in the allowed parameter space the TC2 model can explain the Tevatron measured $A_{FB}$ at $2\sigma$ level, but meanwhile significantly enhance $A_{C}$ at the LHC. Such enhanced $A_{C}$, albeit currently allowed by the LHC measurement at $2\sigma$ level, will serve as a test of TC2 with the improvement of measurement precision at the LHC. Then with all the constraints (including the requirement to explain $A_{FB}$ at $2\sigma$ level and satisfying the current LHC measurement of $A_{C}$ at $2\sigma$ level), we find that the TC2 model can induce sizable triple-top production at the 14 TeV LHC (the production rate can maximally reach 16 pb). Due to the low SM backgrounds, the triple-top production can also be a good probe for TC2 model, complementary to $A_{C}$.- [Show abstract] [Hide abstract]
**ABSTRACT:**The top quark forward-backward asymmetry measured at the Fermilab Tevatron collider deviates from the standard model prediction. A W^prime boson model is described, where the coupling W^prime-t-d is fixed by the tt_bar forward-backward asymmetry and total cross section at the Tevatron. We show that such a W^prime boson would be produced in association with a top quark at the CERN Large Hadron Collider (LHC), thus inducing additional tt_bar+j events. We use measurements of tt_bar+n-jet production from the LHC to constrain the allowed W^prime-t-d couplings as a function of W^prime boson mass. We find that this W^prime model is constrained at the 95% C.L. using 0.7 fb^{-1} of data from the LHC, and could be fully excluded with 5 fb^{-1} of data.

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