Longitudinal quark polarization in \(e^+e^- \to t\overline{t}\) and chromoelectric and chromomagnetic dipole couplings of the top quark

  • S.D. Rindani
  • M.M. Tung
Theoretical physics


The effect of anomalous chromomagnetic (\(\mu\)) and chromoelectric couplings (d) of the gluon to the top quark is considered in \(e^+e^- \to t\overline{t}\), with unpolarized and longitudinally polarized electron beams. The total cross section, as well as t and \(\overline{t}\) polarizations, are calculated to order \(\alpha_s\) in the presence of the anomalous couplings. One of the two linear combinations of t and \(\overline{t}\) polarizations is CP even, while the other is CP odd. The limits that could be obtained at a typical future linear collider with an integrated luminosity of 50 fb\(^{-1}\) and a total c.m. energy of 500 GeV on the most sensitive CP-even combination of anomalous couplings, are estimated as \(-3 < {\rm Re}(\mu) < 2\), for \({\rm Im}(\mu)=0=d\), and \(\sqrt{{\rm Im}(\mu)^2 + \vert d \vert ^2} < 2.25\), for \({\rm Re}(\mu)=0\). There is an improvement by roughly a factor of 2 at 1000 GeV. On the other hand, from the CP-odd combination, we derive the possible complementary bounds as \(-3.6 < {\rm Im} (\mu^* d) < 3.6\), for \({\rm Im} (d) = 0\), and \(-10 < {\rm Im} (d) < 10\), for \({\rm Im} (\mu^* d) = 0\), for a c.m. energy of 500 GeV. The corresponding limit for 1000 GeV is almost an order of magnitude better for \({\rm Im} (\mu^* d)\), though somewhat worse for \({\rm Im} (d)\). Results for the c.m. energies 500 GeV and 1000 GeV, if combined, would yield independent limits on the two CP-violating parameters of \(-0.8 < {\rm Im} (\mu^* d) < 0.8\) and \(-11 <{\rm Im} (d) < 11\).


Linear Combination Electron Beam Total Cross Section Dipole Coupling Linear Collider 
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Copyright information

© Springer-Verlag Berlin Heidelberg 1999

Authors and Affiliations

  • S.D. Rindani
    • 1
  • M.M. Tung
    • 2
  1. 1.Theory Group, Physical Research Laboratory, Navrangpura, Ahmedabad 380 009, India IN
  2. 2.Institute for Theoretical Physics, State University of New York, Stony Brook, NY 11794-3840, USA US

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