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Probing Chirality of Top-Higgs FCNC Couplings at Linear Colliders

We study the nature of the flavor changing neutral couplings of the top quark with the Higgs boson and the up/charm quark in the tt¯ production at linear colliders. There are previous bounds on such tqH couplings at both, linear and hadronic colliders, with the assumption that it couples equally to the left and the right handed fermions. In this paper we examine the chirality of the tqH coupling and construct different observables which will be sensitive to it. It was found that in particular the off-diagonal basis can be useful to distinguish among the chiral tqH couplings. The sensitivity of the unpolarized ILC in probing the couplings at the 3σ level at s√ = 500 GeV and L = 500 fb−1 is also studied, resulting in predicted BR(t → qH) < 1.19 ×10−3. This limit is further improved to BR(t → qH) < 8.84 ×10−4 with the inclusion of initial beam polarization of left handed electrons and right handed positrons.

top quark ; flavor changing neutral couplings ; Higgs

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