The forward-backward asymmetry of top quark production at the Tevatron in warped extra dimensional models

The CDF Collaboration, “Measurement of the Forward-Backward Asymmetry in t ​ t ¯ t\bar{t} Production in 3.2 f ​ b − 1 fb^{-1} of p ​ p ¯ p\bar{p} Collisions at s = 1.96 \sqrt{s}\!=\!1.96 TeV” (March 2009), CDF/ANAL/TOP/PUBLIC/9724; http://www-cdf.fnal.gov/physics/new/top/2009/tprop/Afb/

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There are also contributions to the q ​ q ¯ → t ​ t ¯ q\bar{q}\to t\bar{t} process from the photon and the Z Z boson. However, because of the small EW coupling compared to the QCD coupling and, since these diagrams do not interfere with the one with gluon exchange as a result of color conservation, the contributions are extremely small, <

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Here, we have added to the cross section value given in Ref. Mateo , σ ​ ( t ​ t ¯ ) th = 6.73 − 0.79 + 0.71 \sigma(t\bar{t})^{\rm th}=6.73^{+0.71}_{-0.79} pb, 0.3 0.3 pb to account for the shift generated when using the new NNLO set of parton distribution functions given in: A. Martin, W. Stirling, R. Thorne and G. Watt (MRST Collaboration), Phys. Lett. B652 (2007) 292. Note that these values are for a top quark mass m t = 175 m_{t}=175 GeV, which will be used as normalization; A FB t A_{\rm FB}^{t} does not significantly depend on m t m_{t}

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We have evaluated the contribution of the box diagrams involving squarks and gluinos in the minimal supersymmetric extension of the SM (MSSM) to A FB t A_{\rm FB}^{t} and found that, even for squark and gluino masses close to 100 GeV, the interference with the tree SM diagram with gluon exchange cannot exceed the level of 10 − 4 10^{-4}

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In RSb, the b R b_{R} and b L b_{L} multiplets are in ( 𝟏 , 𝟐 ) ({\bf 1},{\bf 2}) and ( 𝟐 , 𝟑 ) ({\bf 2},{\bf 3}) representations of the custodial SU ​ ( 2 ) L × SU ​ ( 2 ) R {\rm SU(2)_{L}\!\times\!SU(2)_{R}} symmetry. The t R t_{R} and t L t_{L} multiplets are embedded in ( 𝟏 , 𝟐 ) ({\bf 1},{\bf 2}) and ( 𝟐 , 𝟏 ) ({\bf 2},{\bf 1}) multiplets. The b L b_{L} and t L t_{L} multiplets mix together on the ultraviolet boundary resulting in the SM doublet Q L Q_{L} mainly composed by the t L t_{L} multiplet. The representations are universal in flavor

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Work in progress

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C. Bouchart and G. Moreau, Nucl. Phys. B810 (2009) 66

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