Revisiting the top quark chromomagnetic dipole moment in the SM

J. I. Aranda; T. Cisneros-Pérez; J. Montaño; B. Quezadas-Vivian; F. Ramírez-Zavaleta; E. S. Tututi

doi:10.1140/epjp/s13360-021-01102-x

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2024 Impact factor 2.9

EPJ PLUS - Condensed Matter and Complex Systems

Eur. Phys. J. Plus (2021) 136: 164
https://doi.org/10.1140/epjp/s13360-021-01102-x

Regular Article

Revisiting the top quark chromomagnetic dipole moment in the SM

J. I. Aranda¹, T. Cisneros-Pérez¹, J. Montaño¹^,2, B. Quezadas-Vivian¹, F. Ramírez-Zavaleta¹^e and E. S. Tututi¹

¹ Facultad de Ciencias Físico Matemáticas, Universidad Michoacana de San Nicolás de Hidalgo, Av. Francisco J. Mújica s/n, 58060, Morelia, Michoacán, México
² Cátedras Conacyt, Av. Insurgentes Sur 1582, Col. Crédito Constructor, Alc. Benito Juárez, 03940, Ciudad de México, México

^e feramirez@umich.mx

Received: 10 September 2020
Accepted: 9 January 2021
Published online: 2 February 2021

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 ( $q^{2} = 0$ ${q^{2}}=0$ ), generates an infrared divergent pole. Consequently, the chromomagnetic dipole should not be perturbatively evaluated at $q^{2} = 0$ ${q^{2}}=0$ . Focusing on this top quark anomaly, denoted as ${\hat{μ}}_{t} (q^{2})$ $\hat{\mu }_t({q^{2}})$ , we compute it with the off-shell gluon with a large momentum transfer, just as the $α_{s} (m_{Z}^{2})$ $\alpha _s({m_{Z}^{2}})$ convention scale, for both spacelike $q^{2} = - m_{Z}^{2}$ ${q^{2}}=-{m_{Z}^{2}}$ and timelike $q^{2} = m_{Z}^{2}$ ${q^{2}}={m_{Z}^{2}}$ cases. We found that ${\hat{μ}}_{t} (- m_{Z}^{2}) = - 0.0224 - 0.000925 i$ $\hat{\mu }_t(-{m_{Z}^{2}})= -0.0224-0.000925i$ and ${\hat{μ}}_{t} (m_{Z}^{2}) = - 0.0133 - 0.0267 i$ $\hat{\mu }_t({m_{Z}^{2}}) = -0.0133-0.0267i$ . Our $Re {\hat{μ}}_{t} (- m_{Z}^{2})$ $\mathrm {Re} \hat{\mu }_t(-{m_{Z}^{2}})$ matches well with the current experimental value ${\hat{μ}}_{t}^{Exp} = - 0 . 024_{- 0.009}^{+ 0.013} {(stat)}_{- 0.011}^{+ 0.016} (syst)$ $\hat{\mu }_t^{\mathrm {Exp}}=-0.024_{-0.009}^{+0.013}(\mathrm {stat})_{-0.011}^{+0.016}(\mathrm {syst})$ , and the $Im {\hat{μ}}_{t} (- m_{Z}^{2})$ $\mathrm {Im} \hat{\mu }_t(-{m_{Z}^{2}})$ part is induced by flavour changing charged currents.