Higgs mediated flavor violating top quark decays t → uiH, uiγ, uiγγ, and the process γγ → tc in effective theories

The rare top quark couplings tu(i)gamma and tu(i)gamma gamma (u(i) = u, c) induced at the one-loop level by a flavor violating tu(i)H vertex are studied within the context of an effective Yukawa sector that incorporates SUL(2) x U-Y(1)-invariant operators of up to dimension six. Data on the recently observed D-0 - (D) over bar (0) mixing are employed to constrain the tu(i)H vertex, which is then used to predict the t -> u(i)H, t -> u(i)gamma, and t -> u(i)gamma gamma decays, as well as the gamma gamma -> (t) over baru(i) + t (u) over bar (i) reaction in the context of the ILC. It is found that the t -> cH and t -> c gamma gamma decays can reach sizable branching ratios as high as 5 x 10(-3) and 10(-4), respectively. As for the t -> c gamma decay, it can have a branching ratio of 5 x 10(-8) that is about 6 orders of magnitude larger than the standard model prediction, which, however, is still very small to be detected. As for tc production, it is found that, due to the presence of a resonant effect in the convoluted cross section sigma(e(+)e(-) -> gamma gamma -> t (c) over bar + (t) over barc), about (0.5-2.7) x 10(3) tc events may be produced at the ILC for a value of the Higgs mass near to the top mass.