arXiv subjects
Publications and source records attributed to C. Q. Geng.
We study the T violating effects in the baryonic decays of $Λ_b\toΛl^+l^- (l=e ,μ)$ with polarized $Λ$. We show that the transverse $Λ$ polarizations in these baryonic decays could be as large as 50% in CP violating theories beyond the standard model such as the SUSY models, which can be tested in various future hadron colliders.
We explored various cases for the branching ratios (BRs) of $B_s\to K^+K^-$, $B_s\to K^0\bar{K}^0$ and $B_d\to π^+ π^-$ decays. We study the possibility of determining $γ$ by using the following the measurements: (a) BRs of $B_s\to K^+K^-$, and $B_s\to K^0\bar{K}^0$; (b) the ratio of direct CP asymmetries in $B_d\to π^+ π^-$ and $B_s\to K^+K^-$; (c) the mix-induced CP asymmetry in $B_d\to π^+ π^-$; and (d) the angle of $β$.
We study the tensor form factors for $P \to P$ and $P \to V$ transitions in the light-front quark model with $P$ and $V$ being pseudoscalar and vector mesons, respectively. We explore the behaviors of these form factors in the entire physical range of $0\leq p^2\leq (M_i - M_f)^2$. At the maximum recoil of $p^2=0$, we compare our results of the form factors in $B\to π,K,ρ,K^*$ with various other calculations in the literature.
We present a systematic analysis for the rare baryonic exclusive decays of $Λ_b\toΛl^+ l^- (l=e,μ,τ)$. We study the differential decay rates and the di-lepton forward-backward, lepton polarization and various CP asymmetries with a new simple set of form factors inspired by the heavy quark effective theory. We show that most of the observables are insensitive to the non-perturbative QCD effects. To illustrate the effect of new physics, we discuss our results in an explicit supersymmetric extension of the standard model, which contains new CP violating phases and therefore induces sizable CP violating asymmetries.
We study the contribution of a generic charged Higgs $(H^+)$ to the muon anomalous magnetic moment $a_μ$ with the SUSY soft breaking parameters. We find out that the deviation between the experimental data and the predicted SM value on $a_μ$ can be explained by the two-loop charged Higgs diagrams even with $m_{H^+}\sim 400 GeV$.
We study the dilepton forward-backward and the longitudinal, normal and transverse lepton polarization asymmetries in the heavy baryon decays of $Λ_b\toΛl^+l^-$. We show that the asymmetries have a less dependence on the non-perturbative QCD effects. In the standard model, we find that the integrated forward-backward asymmetries (FBAs) and three components of the polarizations in the QCD sum rule approach (pole model) are $-0.13\ (-0.12)$ and $(58.3,-9.4,-0.07)%$ ($(58.3,-12.6,-0.07)%$) for $Λ_b\toΛμ^+μ^-$ and $-0.04 (-0.03)$ and $(10.9,-10.0,-0.39)%$ ($(10.9,-0.2,-0.34)%$) for $Λ_b\toΛτ^+τ^-$, respectively.
We investigate the rare baryonic exclusive decays of $Λ_b\to Λl^+ l^- (l=e,μ,τ)$ with polarized $Λ$. Under the approximation of the heavy quark effective theory (HQET), in the standard model we derive the differential decay rates and various polarization asymmetries by including lepton mass effects. We find that with the long-distance effects the decay branching ratios are $5.3\times 10^{-5}$ for $Λ_b\to Λl^+ l^-\ (l=e,μ)$ and $1.1\times 10^{-5}$ for $Λ_b\to Λτ^+τ^-$. The effects of new physics in the decay rates are also discussed. The integrated longitudinal $Λ$ polarizations are -0.31 and -0.12, while that of the normal ones 0.02 and 0.01, for di-muon and tau modes, respectively. The CP-odd transverse polarization of $Λ$ is zero in the standard model but it is expected to be sizable in some theories with new physics.
We first review the three known chiral anomalies in four dimensions and then use the anomaly free conditions to study the uniqueness of quark and lepton representations and charge quantizations in the standard model. We also extend our results to theory with an arbitrary number of color. Finally, we discuss the family problem.
We study the radiative leptonic $D$ meson decays of $D^+_{(s)}\to ł^+ν_łγ$ ($ł=e,μ,τ$), $D^0\to ν\barνγ$ and $D^0\to ł^+ł^-γ$ ($l=e,μ$) within the light front quark model. In the standard model, we find that the decay branching ratios of $D^+_{(s)}\to e^+ν_eγ$, $D^+_{(s)}\toμ^+ν_μγ$ and $D^+_{(s)}\toτ^+ν_τγ$ are $6.9\times 10^{-6}$ ($7.7\times 10^{-5}$), $2.5\times 10^{-5}$ ($2.6\times 10^{-4}$), and $6.0\times 10^{-6}$ ($3.2\times 10^{-4}$), and that of $D^0\toł^+ł^-γ$ ($ł=e,μ$) and $D^0\toν\barνγ$ are $6.3\times 10^{-11}$ and $2.7\times 10^{-16}$, respectively.
We investigate the decay of $Λ_b\toΛν\barν$ with the polarized baryons of $Λ_b$ and $Λ$. With the most general hadronic form factors, we first study the decay branching ratio and then derive the longitudinal, normal and transverse polarizations of $Λ$ in terms of the spin unit vectors of $Λ_b$ and $Λ$ and the momentum of $Λ$. A polarization of $Λ_b$ is also discussed.
We present a general analysis on charmless B-meson decays $B\to ππ$ and $πK$. It is noticed that the final state interactions and inelastic rescattering effects must be significant in order to understand the consistency of the current data. By using general isospin decompositions, the isospin amplitudes and the corresponding strong phases could be extracted from a global $χ^2$ fit of the experimental data. We emphasize that in general there are two, rather than one, relative strong phases in the decomposition. In the assumption of two equalstrong phases as considered in the literature, the current data, especially the ones concerning $B\to π^0 K^{0(\pm)}$decays, will imply a large isospin amplitude $|a^c_{3/2}| > 40 $, which is larger by a factor of five than the one from the naive factorization estimation. When two different strong phases are considered, all the isospin amplitudes can become, within the $1σ$-level, comparable with the theoretical values. We also show that the difference between the two strong phases cannot be too large and will be restricted by the most recent upper bound of $B\to π^0π^0$ decay. In any case, the strong phases are found to be large and the branching ratio of $B\to π^0π^0$ is likely to be enhanced by an order of magnitude in comparison with the one obtained from the naive factorization approach. Direct CP violations in all decay modes are also calculated and found to be close to the sensitivity of the present experiments.
We study the decays of $B_{s,d} \to l^+ l^- γ(l=e, μ,τ)$ within the light-front model. We calculate the tensor type form factors and use these form factors to evaluate the decay branching ratios. We find that, in the standard model, the branching ratios of $B_{s(d)} \to ł^+ ł^- γ$ ($ł=e, μ,τ$) are $7.1\times 10^{-9}$ ($1.5\times 10^{-10}$), $8.3\times 10^{-9}$ ($1.8\times 10^{-10}$), $1.6\times 10^{-8}$ ($6.2\times 10^{-10}$), respectively.
We study the CP conserving and violating contributions to the decay of $\knng$ in the standard model. In our analysis, we use the form factors for $K\toγ$ transitions calculated directly in the entire physical range of momentum transfer within the light front model. We find that the branching ratios for the CP conserving and violating parts are about $1.0\times 10^{-13}$ and $1.5\times 10^{-15}$, respectively.
We study the lepton polarization asymmetries in the radiative leptonic B decays of $B^+\to l^+ν_{l}γ$ and $B^+_{c}\to l^+ν_{l}γ$. We concentrate on the transverse component of the $τ$ lepton asymmetries in the tau decay modes due to CP violation in theories beyond the standard model to search T violating effect.
Within the light front framework, we calculate the form factors for $B\toγ$ transitions directly in the entire physical range of momentum transfer. Using these form factors, we study the radiative decays of $B\to lν_lγ$ and $B_{s(d)}\toν\barνγ$. We show that the decay rates of $B\to lν_lγ(l=e,μ)$ and $B\toν\barνγ$ are larger than that of the corresponding purely leptonic modes. Explicitly, in the standard model, we find that the branching ratios of $B\to μν_μγ$ and $B_s\toν\barνγ$ are $3.7\times 10^{-6}$ and $5.0\times 10^{-8}$, in contrast with $3\times 10^{-7}$ and 0 for $B\toμν_μ$ and $B\toν\barν$, respectively.
We study the T violating transverse muon polarization in the decay of $K^+\to μ^+νγ$ due to CP violation in theories beyond the standard model. We find that the polarization asymmetry could be large in some CP violation models and it may be detectable at the ongoing KEK experiment of E246 as well as the proposed BNL experiment.
We investigate the longitudinal lepton polarization asymmetry in the exclusive processes $B\to K l^+l^-$ and $B\to K^* l^+l^-$. We include both short and long-distance contributions to the asymmetry in our discussions. We find that average values of the polarization asymmetries of the muon and tau for $B\to K^{(*)}μ^+μ^-$ and $B\to K^{(*)}τ^+τ^-$ are $-0.8\ (-0.7)$ and $-0.2\ (-0.5)$, respectively.
We calculate long distance contributions to $K\toπν\barν\,,\ ππν\barν$, and $πππν\barν$ modes within the framework of chiral perturbation theory. We find that these contributions to decay rates of $K\to πν\barν$ and $K\to ππν\barν$ in the chiral logarithmic approximation are at least seven orders of magnitude suppressed relative to those from the short distance parts. The long distance effects in this class of decays are therefore negligible.