Transverse beam polarization and limits on leptoquark couplings in e+e-   --> t tbar
  It is shown that if electron and positron beams at a linear collider are transversely polarized, azimuthal asymmetries of the final-state top quark in e+e- --> t tbar can be used to probe a combination of couplings of left and right chiralities in a scalar leptoquark model. The CP-conserving azimuthal asymmetry would be a sensitive test of the chirality violating couplings. A linear collider operating at sqrt{s}=500 GeV and having transverse polarizations of 80% and 60% respectively for the e- and e+ beams, can put a limit of the order of 0.025 on the product of the left and right chirality leptoquark couplings (in units of the electromagnetic coupling constant), with a leptoquark mass of 1 TeV and for an integrated luminosity of 500 inverse fb. The CP-violating azimuthal asymmetry, which would provide a direct test of CP-violating phases in leptoquark couplings, can be constrained to the same level of accuracy. However, this limit is uninteresting in view of the much better indirect limit from the electric dipole moment of the electron. 
Saurabh D. Rindani