Single top production at the next generation linear e+e- colliders

Present limits on the top mass from LEP1 and Tevatron point to a top quark that is considerably heavier than the W vector boson in the standard model; e+e- colliders with √s≅300 GeV (the c.m. energy foreseen at the first phase of the next linear e+e- collider) could be well below the energy threshold for real top-pair production. We argue that, if this is the case, single top production through the process e+e-→t anti bW-( anti tbW+), where t anti b( anti tb) are produced mainly by means of a virtual W, becomes the dominant top production mechanism. Total cross sections and kinematical distributions are evaluated and numerical results are given in ranges of mt and √s where single top production can be of relevance. The relative importance of virtual-W and virtual-t contributions to the process is discussed. (orig.)