A minimal set of top anomalous couplings

Abstract We simplify the general form of the fermion–fermion–gauge boson interactions generated by dimension-six gauge-invariant effective operators by using the equations of motion to remove redundant operators. It is found that the most general vertex for off-shell fermions f i , f j and an off-shell boson V = W , Z , γ , g only involves γ μ and σ μ ν q ν terms, with q = p i − p j . Examples are given for the Wtb , Ztt , γtt and gtt interactions, whose general expression is greatly simplified with respect to previous results in the literature. The same arguments apply to top flavour-changing neutral interactions with the Z boson, the photon or the gluon, which can also be parameterised in full generality with only γ μ and σ μ ν q ν couplings. Explicit expressions are given for these vertices in terms of dimension-six gauge-invariant operators. We also discuss how effective operator coefficients might be determined from eventual measurements of anomalous couplings.

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