Top Quark Flavor Changing Decay t→ cH^0 in Little Higgs Model

We study theoretically the quantum effects of the littlest Higgs model (LH) mediated by flavor changing one-loop Feynman diagrams on the rare decay process t → cH0. The comparison of the decay width in the LH model with that in the standard model (SM) is made. We find that the decay branch ratio of t → cH0 in the LH model is at most of the order ～ 10-12, which is two order larger than in the SM. The numerical results show that the difference between the branch ratios in the LH model and the SM is generally sensitive to the LH model parameters, such as symmetry breaking scale f, Higgs boson mass mH0, and x = v'4f /v2 in our chosen parameter space, but relatively insensitive to the value choice of the cosine of the mixing angle c and the ratio λ1/λ2.

The Production of Pseudo Goldstone Boson in Top Quark Rare Decay

We calculate the flavor changing decay in the framework of the topcolor assisted multiscale technicolor model. We find that (a) the branching ratio of is insensitive to and , while it increases quickly as increases; (b) for reasonable ranges of the parameters, the maximum of the branching ratio in this model may reach , seven orders larger compared to the one calculated in the standard model. This might provide an opportunity to detect the rare decay of the top quark in experiments.

Investigations on the charmless decays of Y(4260)

Apart from the charmful decay channels of Y（4260）, the charmless decay channels of Y（4260） also provide us a good platform to study the nature and the decay mechanism of Y（4260）. In this paper, we propose to probe the structure of Y（4260） through the charmless decays Y（4260）→VP via intermediate D1D＋c.c. meson loops, where V and P stand for light vector and pseudoscalar mesons, respectively. Under the molecule ansatz of Y（4260）, the predicted total branching ratio BRVP for all Y（4260） → VP processes are about（0.34＋0.32-0.23）% to（0.75＋0.72-0.52）% with the cutoff parameter α=2–3. Numerical results show that the intermediate D1D＋c.c. meson loops may be a possible transition mechanism in the Y（4260） → VP decays. These predicted branching ratios are the same order to that of Y（4260）→Z＋c（3900）π-, which may be an evidence of D1 D molecule and can be examined by the forthcoming BESdata in the near future.

b→ssd decay in Randall-Sundrum models

The extremely small branching ratio of the b → ssd decay in the Standard Model makes it a suitable channel to explore new-physics signals.We study this ？S = 2 process in Randall-Sundrum models,including the custodially protected and the bulk-Higgs Randall-Sundrum models.Exploring the experimentally favored parameter spaces of these models suggests a possible enhancement of the decay rate,compared to the Standard Model result,by at most two orders of magnitude.

Why static bound-state calculations of tetraquarks should be met with scepticism

Recent experimental signals have led to a revival of tetraquarks,the hypothetical q~2q~2 hadronic states proposed by Jaffe in 1976 to explain the light scalar mesons.Mesonic structures with exotic quantum numbers have indeed been observed recently,though a controversy persists as to whether these are true resonances and not merely kinematical threshold enhancements,or otherwise states not of a true q~2q~2 nature.Moreover,puzzling non-exotic mesons are also often claimed to have a tetraquark configuration.However,the corresponding model calculations are practically always carried out in pure and static bound-state approaches,ignoring completely the coupling to asymptotic two-meson states and unitarity,especially the dynamical effects thereof.In this short paper we argue that these static predictions of real tetraquark masses are highly unreliable and provide little evidence of the very existence of such states.

D*D1(2420)and D D'*(2600)interactions and the charged charmonium-like state Z(4430)

The D＊ D1（2420） and DD ＇＊（2600） interactions are studied in a one-boson-exchange model. Isovector bound state solutions with spin parity J^P= 1^＋are found from the D＊ D1（2420） interaction, which may be related to the observed charged charmonium-like state Z（4430）. There is no bound state solution found from the DD ＇＊（2600）interaction.