Higgs mediated flavor violating top quark decays t --> u_i H, u_i gamma, u_i gamma gamma, and the process gamma gamma --> t c in effective theories

Abstract

The rare top quark couplings $t{u}_i\gamma$ and $t{u}_i\gamma \gamma$ ($u_i=u,c$) induced at the one-loop level by a flavor violating $t{u}_{i}H$ vertex are studied within the context of an effective Yukawa sector that incorporates $S{U}_L(2)\times U_Y(1)$-invariant operators of up to dimension six. Data on the recently observed $D^0-\overline{D^0}$ mixing are employed to constrain the $t{u}_{i}H$ vertex, which is then used to predict the $t\to u_{i}H$, $t\to u_i\gamma$, and $t\to u_i\gamma \gamma$ decays, as well as the $\gamma \gamma \to \bar{t}{u}_i+t{\bar{u}}_i$ reaction in the context of the ILC. It is found that the $t\to cH$ and $t\to c\gamma \gamma$ decays can reach sizable branching ratios as high as $5\times 10^{-3}$ and $10^{-4}$, respectively. As for the $t\to c\gamma$ decay, it can have a branching ratio of $5\times 10^{-8}$ 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 $\sigma (e^{+}{e}^{-}\to \gamma \gamma \to t\bar{c}+\bar{t}c)$, about $(0.5-2.7)\times 10^3$ $tc$ events may be produced at the ILC for a value of the Higgs mass near to the top mass.

Comments: 5 pages and 3 figures