Top quark forward-backward asymmetry at the Tevatron: a comparative study in different new physics models

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The top quark forward-backward asymmetry AFBᵗ measured at the Tevatron is above the Standard Model prediction by more than 2-sigma deviation, which might be a harbinger for new physics. In this work we examine the contribution to AFBᵗ in two different new physics models: one is the minimal supersymmetric model without R-parity (RPV-MSSM) which contributes to AFBᵗ via sparticle-mediated t-channel process d dbar-> t tbar; the other is the third-generation enhanced left-right model (LR model) which contributes to AFBᵗ via Z'-mediated t-channel or s-channel processes. We find that in the parameter space allowed by the ttbar production rate and the ttbar invariant mass distribution at the Tevatron, the LR model can enhance AFBᵗ to within the 2-sigma region of the Tevatron data for the major part of the parameter space, and in optimal case AFBᵗ can reach 12% which is slightly below the 1-sigma lower bound. For the RPV-MSSM, only in a narrow part of the parameter space can the λ'' couplings enhance AFBᵗ to within the 2-sigma region while the λ' couplings just produce negative contributions to worsen the fit.