Kek–th–759 Msuhep–010401

We consider the single production of charged Higgs bosons H of the twoHiggs-doublet model in eγ collisions through the production subprocess eγ → νH. As the production rate is governed by the size of the loop-induced HWγ coupling, the cross section can only be substantial for smaller values of tanβ, tanβ . 1, where the top-bottom loop contribution is enhanced. In this case, however, the natural width of the charged Higgs boson becomes large so that the Standard Model continuum background becomes important. We study the background subprocess eγ → νt̄b including the interference with the signal, and find that in the region of charged Higgs mass that can be interesting, the signal is difficult to detect. Multi-doublet Higgs sectors arise naturally in several extensions of the StandardModel (SM) including the Minimal Supersymmetric Standard Model (MSSM), and these give rise to the charged Higgs boson H. Its discovery at present and future collider experiments has been the subject of much debate, but it remains that the large mass region is elusive. Here we study the single production channel, eγ → νH, (1) in the eγ option of future linear colliders. The process involves the HWγ vertex [2] which is forbidden at tree level because of gauge invariance, and is therefore loop-induced. The main motivation for considering this process is as a discovery mode. Although the physics potential of the eγ option is limited compared to the ee and γγ options, it is possible that earlier experiments See ref. [1] and the references therein for a review of the current status.