Search

We study the long-distance contribution to ${B}_{s}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$ decay, which is generated by the two-photon intermediate state via the ${B}_{s}\ensuremath{\rightarrow}{\ensuremath{\gamma}}^{*}{\ensuremath{\gamma}}^{*}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$ transition. It is found that the dispersive two-photon amplitude can interfere with the dominant short-distance amplitude, which gives rise to new theoretical uncertainty in the branching ratio of ${B}_{s}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$. Our analysis shows that, by taking into account present experimental constraints, this uncertainty could be up to the same order of magnitude as some theoretical uncertainties of $\mathcal{B}({B}_{s}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}})$ given in the past literature. Future precise studies of the double radiative ${B}_{s}\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\gamma}$ decay, both experimentally and theoretically, may help to reduce the uncertainty. This novel effect has never been examined in ${B}_{s}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$ decay.

Rare weak decays of ${\ensuremath{\eta}}^{\ensuremath{'}}\ensuremath{\rightarrow}K\ensuremath{\pi}$ have been investigated in the framework of the $U(3)$ chiral perturbation theory at the leading order. Our study shows that the branching ratio $\mathcal{B}({\ensuremath{\eta}}^{\ensuremath{'}}\ensuremath{\rightarrow}K\ensuremath{\pi})$ is of the order of ${10}^{\ensuremath{-}11}$, which is far below the present experimental upper bound given by the BESIII Collaboration. By further analysis of ${\ensuremath{\eta}}^{\ensuremath{'}}\ensuremath{\rightarrow}{K}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ and ${\ensuremath{\eta}}^{\ensuremath{'}}\ensuremath{\rightarrow}{K}^{0}{\ensuremath{\pi}}^{0}$, the ratio of isospin amplitudes is found, $|{A}_{1/2}/{A}_{3/2}|\ensuremath{\simeq}35$, which supports that the $\mathrm{\ensuremath{\Delta}}I=1/2$ transition enhancement, namely, the $\mathrm{\ensuremath{\Delta}}I=1/2$ rule, could be functional in ${\ensuremath{\eta}}^{\ensuremath{'}}$ weak decays.

Motivated by the experimental study of $J/\psi\to\gamma ~+$ invisible decay by the CLEO Collaboration, we analyze the process $J/\psi\to \gamma \nu\bar{\nu}$, as the standard model background for this invisible decay, at the lowest order. Our investigation shows that Br($J/\psi\to \gamma \nu\bar{\nu}$) is far below the present experimental upper limit on the branching ratio of $J/\psi\to\gamma ~+$ invisible, which indicates that some interesting room for new physics in this channel might be expected. We also present a similar analysis of the $\eta_c\to \gamma \nu\bar{\nu}$ decay.

Using the Higgs boson mass ${m}_{h}=125\text{ }\text{ }\mathrm{GeV}$, the radiative Higgs decays $h\ensuremath{\rightarrow}\ensuremath{\gamma}{\ensuremath{\nu}}_{l}{\overline{\ensuremath{\nu}}}_{l}$ with ${\ensuremath{\nu}}_{l}={\ensuremath{\nu}}_{e}$, ${\ensuremath{\nu}}_{\ensuremath{\mu}}$, and ${\ensuremath{\nu}}_{\ensuremath{\tau}}$ are analyzed in the standard model. Our calculation shows that the inclusive width of these processes, i.e., the sum of $\mathrm{\ensuremath{\Gamma}}(h\ensuremath{\rightarrow}\ensuremath{\gamma}{\ensuremath{\nu}}_{l}{\overline{\ensuremath{\nu}}}_{l})$ for ${\ensuremath{\nu}}_{l}={\ensuremath{\nu}}_{e}$, ${\ensuremath{\nu}}_{\ensuremath{\mu}}$, ${\ensuremath{\nu}}_{\ensuremath{\tau}}$, is 1.41 keV, which is about 15% of $\mathrm{\ensuremath{\Gamma}}(h\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\gamma})$. Therefore, the observation of these channels in future precise experiments may provide some useful information on the Higgs physics in both the standard model and its possible extensions.

To one-loop order and $O({\ensuremath{\alpha}}_{\mathrm{EM}}),$ the electromagnetic mass splittings of \ensuremath{\pi}, ${a}_{1},$ $K,$ ${K}_{1}(1400),$ and ${K}^{*}(892)$ are calculated in the framework of $\mathrm{U}{(3)}_{L}\ifmmode\times\else\texttimes\fi{}\mathrm{U}{(3)}_{R}$ chiral field theory. The logarithmic divergences emerging in the Feynman integrations of the mesonic loops are factorized by using an intrinsic parameter $g$ of this theory. No other additional parameters or counterterms are introduced to absorb the mesonic loop divergences. When ${f}_{\ensuremath{\pi}},$ ${m}_{\ensuremath{\rho}},$ and ${m}_{a}$ are taken as inputs, the parameter $g$ will be determined and all the physical results are finite and fixed. Dashen's theorem is satisfied in the chiral SU(3) limit of this theory and a rather large violation of the theorem is revealed at the order of ${m}_{s}$ or ${m}_{K}^{2}.$ Mass ratios of light quarks have been determined. A relation for electromagnetic corrections to masses of axial-vector mesons is obtained. It could be regarded as a generalization of Dashen's theorem. Comparing with data, it is found that the nonelectromagnetic mass difference of ${K}^{*}$ is in agreement with the estimation of Schechter, Subbaraman, and Weigel.

Based on experimental data by the Belle Collaboration, we present a phenomenological analysis of the angular distributions in ${\ensuremath{\tau}}^{\ensuremath{-}}\ensuremath{\rightarrow}{K}_{S}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\nu}}_{\ensuremath{\tau}}$ decay. Our study shows that the angular analysis could lead to some interesting observables, and the future experimental investigation of these observables might be very helpful in revealing the nature of the scalar components of the decay. New physics contributions from the two-Higgs-doublet model to this decay have also been examined.

We study possible scalar type interactions in tau^- -->pi^- pi^0 nu_tau decay. One finds that an angular distribution asymmetry, A(s), can be induced from the interference between the scalar part and vector part amplitudes in this decay. Our analysis shows that, in the two-Higgs-doublet model of type II with large tan beta, the charged Higgs contribution could make A(s) up to 10^{-3} without conflict with present experimental constraints. Thus in the future precise experiments in tau-charm factories, this angular distribution asymmetry may be an interesting observable either to be helpful in searching for the signal of the charged Higgs boson or to impose the significant bound on it.

The CP-violating charge asymmetry in decays K+- --> \pi+- \gamma\gamma, which is induced by the electromagnetic penguin operators, has been studied both in thestandard model and in its extensions. Because of a large enhancement of the Wilson coefficients of the electromagnetic penguin operators in the supersymmetric extensions of the standard model, a significant upper bound on this charge asymmetry could be expected, and thus high precision measurements of this interesting CP-violating quantity might explore new physics effects beyond the standard model.

We revisit the calculation of the long-distance contribution to the muon-polarization asymmetry LR ,w hich arises, inK + ! ++ , from the two-photon intermediate state. The parity-violating amplitude of this process, induced by the local anomalous K + transition, is analysed; unfortunately, one cannot expect to predict its contribution to the asymmetry by using chiral perturbation theory alone. Here we evaluate this amplitude and its contribution to LR by employing a phenomenological model called the FMV model, in which the utility of the vector and axial-vector resonances exchange is important to soften the ultraviolet behaviour of the transition. We nd that the long-distance contribution is of the same order of magnitude as the standard model short-distance contribution.

In the framework of $\mathrm{U}(3{)}_{L}\ifmmode\times\else\texttimes\fi{}\mathrm{U}(3{)}_{R}$ chiral theory of mesons, $\ensuremath{\pi}K$ elastic scattering is studied. The s-wave and p-wave scattering lengths ${(a}_{0}^{3/2}, {a}_{0}^{1/2}, {a}_{1}^{3/2},$ and ${a}_{1}^{1/2})$ and phase shifts $({\ensuremath{\delta}}_{0}^{3/2}, {\ensuremath{\delta}}_{0}^{1/2}, {\ensuremath{\delta}}_{1}^{3/2},$ and ${\ensuremath{\delta}}_{1}^{1/2}),$ the total elastic scattering cross section ${\ensuremath{\sigma}}_{\mathrm{tot}}({\ensuremath{\pi}}^{+}{K}^{+})$ and ${\ensuremath{\sigma}}_{\mathrm{tot}}({\ensuremath{\pi}}^{\ensuremath{-}}{K}^{+}),$ and the p-wave cross section ${\ensuremath{\sigma}}_{p}({\ensuremath{\pi}}^{\ensuremath{-}}{K}^{+})$ are calculated. Theoretical results are in agreement with the experimental data. There is no new parameter in this study.