The top quark chromomagnetic dipole moment in the SM from the 4-body vertex function

Abstract

Abstract A new proposal to compute the anomalous chromomagnetic dipole moment of the top quark, μ ˆ t , in the Standard Model is presented. On the basis of the five-dimensional effective Lagrangian operator that characterizes the quantum-loop induced chromodipolar vertices gt t ¯ and ggt t ¯ , the μ ˆ t anomaly is derived via radiative correction at the 1-loop level from the non-Abelian 4-body vertex function ggt t ¯ . We evaluate μ ˆ t ( s ) as a function of the energy scale s = ±E 2, for E = [10, 1000] GeV, taking into account the running of the quark masses and alpha strong through the MS ¯ scheme. In particular, we find that at the typical energy scale E = m Z for high-energy physics, similarly to α s ( m Z 2 ) , α ( m Z 2 ) and s W ( m Z 2 ) , the spacelike evaluation yields μ ˆ t ( − m Z 2 ) = −0.025 + 0.00384i and the timelike μ ˆ t ( m Z 2 ) = −0.0318 − 0.0106i. This Re μ ˆ t ( − m Z 2 ) = −0.025 from ggt t ¯ is even closer to the experimental central value μ ˆ t Exp = −0.024, than that coming from the known 3-body vertex function gt t ¯ , −0.0224. Once again, the Im μ ˆ t ( − m Z 2 ) part is due to the contribution of virtual charged currents, just like in the gt t ¯ case. We can infer that the spacelike prediction is the favored one.