Revisiting the top quark chromomagnetic dipole moment in the SM

Abstract: We revisit the anomalous chromomagnetic dipole moment in the Standard Model and show that its triple gluon vertex contribution, with the on-shell gluon ($q<sup>2=0$), generates an infrared divergent pole. Consequently, the chromomagnetic dipole should not be perturbatively evaluated at $q<sup>2=0$. Focusing on this top quark anomaly, denoted as $\hat{\mu}<em>t(q<sup>2)$, we compute it with the off-shell gluon with a large momentum transfer, just as the $\alpha_s(m_Z<sup>2)$ convention scale, for both spacelike $q<sup>2=-m_Z<sup>2$ and timelike $q<sup>2=m_Z<sup>2$ cases. We found that $\hat{\mu}_t(-m_Z<sup>2)$ $=$ $-0.0224$ $-0.000925i$ and $\hat{\mu}_t(m_Z<sup>2)$ $=$ $-0.0133$ $-0.0267i$. Our $\mathrm{Re}\thinspace\hat{\mu}_t(-m_Z<sup>2)$ matches well with the current experimental value $$\hat{\mu}_t^{\mathrm{Exp}=-0.024}</em>{-0.009}<sup>{+0.013}(\mathrm{stat})_{-0.011}<sup>{+0.016}(\mathrm{syst})$$, and the $\mathrm{Im}\thinspace\hat{\mu}_t(-m_Z<sup>2)$ part is induced by flavour changing charged currents.