Revisiting the top quark chromomagnetic dipole moment in the SM

• Published in: arXiv.org 2021-01
• Main Authors: Aranda, J I, Cisneros-Pérez, T, Montaño, J, Quezadas-Vivian, B, Ramírez-Zavaleta, F, Tututi, E S
• Format: Article
• Language: English
• Subjects: Dipole moments; Flavor (particle physics); Gluons; Momentum transfer; Quarks; Standard model (particle physics)
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.2009.05195

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