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Chao-Qiang Geng

Publications and source records attributed to Chao-Qiang Geng.

At least 181 records · Page 10Linked to original sources
arXiv2008

Flavors and Phases in Unparticle Physics

Inspired by the recent Georgi's unparticle proposal, we study the flavor structures of the standard model (SM) particles when they couple to unparticles. At a very high energy scale, we introduce $\BZ$ charges for the SM particles, which are universal for each generation and allow $\BZ$ fields to distinguish flavor generations. At the $Λ_{\UP}$ scale, $\BZ$ operators and charges are matched onto unparticle operators and charges, respectively. In this scenario, we find that tree flavor changing neutral currents (FCNCs) can be induced by the rediagonalizations of the SM fermions. As an illustration, we employ the Fritzsch ansatz to the SM fermion mass matrices and we find that the FCNC effects could be simplified to be associated with the mass ratios denoted by $\sqrt{m_{i}m_{j}/m^2_{3}}$, where $m_3$ is the mass of the heaviest particle in each type of fermion generations and $i, j$ are the flavor indices. In addition, we show that there is no new CP violating phase beside the unique one in the CKM matrix. We use $\bar B_{q}\to \ell^{+} \ell^{-}$ as examples to display the new FCNC effects. In particular, we demonstrate that the direct CP asymmetries in the decays can be $O(10%)$ due to the peculiar CP conserving phase in the unparticle propagator.

hep-ph↗
arXiv2008

Same-sign single dilepton productions at the LHC

We examine the same-sign single dilepton productions of $\ell_i^{\pm}\ell_j^{\pm} (\ell_{i,j}=e,μ)$ in high-energy proton-proton collisions at the Large Hadron Collider (LHC) in models with doubly charged Higgs scalars as well as heavy Majorana neutrinos. We demonstrate that these spectacular productions can be detected at the LHC for a class model in which the doubly charged Higgs scalars couple only to the right-handed charged leptons. The ranges of the possible doubly charged Higgs masses and mixings to observe the processes at the LHC are discussed.

hep-ph↗
arXiv2007

Analysis of $K^+ \to e^+ ν_{e}γ$ in light-front quark model and chiral perturbation theory of order $p^6$

Within the frameworks of the light-front quark model (LFQM) and chiral perturbation theory (ChPT) of $O(p^6)$, we reevaluate the form factors of the $K^+ \to γ$ transition. We use these form factors to study the decay of $K^+ \to e^+ ν_{e}γ$, which is dominated by the structure dependent contribution. We show the differential decay branching ratio as a function of $x=2E_γ/m_K$, where $E_γ$ ($m_K$) is the photon energy (kaon mass). Explicitly, we find that, in the standard model with the cut of $x=0.01$ (0.1), the decay branching ratio of $K^+ \to e^+ ν_{e}γ$ is $1.54 (1.44)\times 10^{-5}$ and $1.57 (1.47)\times 10^{-5}$ in the LFQM and ChPT, respectively.

hep-ph↗
arXiv2007

Unparticle physics on direct CP violation

The effects of the peculiar CP conserving phases in unparticle propagators are explored. We find that the phases have a great impact on CP-violation. We adopt the decays $B_{d}\to π^{+} π^{-}$ and $B_{d}\to \ell^{-}\ell^{+}$ as the illustrators to demonstrate the influences of these phases on the direct CP asymmetries. In particular, we emphasize that unparticle physics is the only model suggested to date that could give the direct CP asymmetries in $B_d\to \ell^{-} \ell^{+}$ as large as 15%. We also point out that the unparticle phases could be probed in $B\to K^* \ell^{+} \ell^{-}$ decays by using T-odd correlations.

hep-ph↗
arXiv2007

D-\bar D mixing and rare D decays in the Littlest Higgs model with non-unitarity matrix

We study the $D-\bar D$ mixing and rare D decays in the Littlest Higgs model. As the new weak singlet quark with the electric charge of 2/3 is introduced to cancel the quadratic divergence induced by the top-quark, the standard unitary $3\times 3$ Cabibbo-Kobayashi-Maskawa matrix is extended to a non-unitary $4\times 3$ matrix in the quark charged currents and Z-mediated flavor changing neutral currents are generated at tree level. In this model, we show that the $D-\bar D$ mixing parameter can be as large as the current experimental value and the decay branching ratio (BR) of $D\to X_u \ga$ is small but its direct CP asymmetry could be $O(10%)$. In addition, we find that the BRs of $D\to X_u \ell^{+} \ell^{-}$, $D\to X_uν\bar ν$ and $D\to μ^{+} μ^{-}$ could be enhanced to be $O(10^{-9})$, $O(10^{-8})$ and $O(10^{-9})$, respectively.

hep-ph↗
arXiv2007

Unparticle phase effects

Unparticles proposed by Georgi carry CP conserving phases in their propagators. We demonstrate that these peculiar phases have an important impact on CP violation. Without including the strong QCD phases, we study the unparticle phase effects on the direct CP asymmetries in the exclusive decays of $\bar B_d\to π^{+} π^{-}$ and $B\to πK$, in which the flavor changing neutral currents are forbidden at tree level but induced by one-loop diagrams. Interesting and consistent results comparing to the data are obtained. In addition, we find that unparticles will significantly enhance the differential branching ratio of $b\to s \ell^{+} \ell^{-}$ at the small invariant mass of $\ell^{+} \ell^{-}$. The forward-backward asymmetries for $b\to s \ell^{+} \ell^{-}$ due to unparticles are also explored.

hep-ph↗
arXiv2007

Study of $B \to K_0^* (1430)\ell\bar{\ell} $ Decays

We examine the exclusive rare decays of $B \to K_{0}^*(1430)\ell\bar{\ell} $ with $K_{0}^*(1430)$ being the p-wave scalar meson and $\ell=ν,e,μ,τ$ in the standard model. The form factors for the $B\to K_{0}^{*}$ transition matrix elements are evaluated in the light front quark model. For the decays of $B \to K_{0}^*\ell\bar{\ell}$, the branching ratios are found to be $(11.6,1.63,1.62,0.029)\times 10^{-7}$ with $\ell=(ν,e,μ,τ)$ and the integrated longitudinal lepton polarization asymmetries $(-0.97,-0.95,-0.03)$ with $\ell=(e,μ,τ)$, respectively.

hep-ph↗
arXiv2007

$B\to η^{(\prime)} (\ell^{-} \barν_{\ell}, \ell^{+} \ell^{-}, K, K^*)$ decays in the quark-flavor mixing scheme

In the quark-flavor mixing scheme, $η$ and $η'$ are linear combinations of flavor states $η_{q}=(u\bar{u}+d\bar{d})/\sqrt{2}$ and $η_{s}=s\bar{s}$ with the masses of $m_{qq}$ and $m_{ss}$, respectively. Phenomenologically, $m_{ss}$ is strictly fixed to be around 0.69, which is close to $\sqrt{2m^{2}_{K}-m^{2}_π}$ by the approximate flavor symmetry, while $m_{qq}$ is found to be $0.18\pm 0.08$ GeV. For a large allowed value of $m_{qq}$, we show that the BRs for $B\to η^{(\prime)} X$ decays with $X=(\ell^{-} \barν_{\ell}, \ell^{+} \ell^{-})$ are enhanced. We also illustrate that $BR(B\toηX)> BR(B\to η^{\prime} X)$ in the mechanism without the flavor-singlet contribution. Moreover, we demonstrate that the decay branching ratios (BRs) for $B\to η^{(\prime)}K^{[*]}$ are consistent with the data. In particular, the puzzle of the large $BR(B\to η^{\prime} K)$ can be solved. In addition, we find that the CP asymmetry for $B^{\pm}\to ηK^{\pm}$ can be as large as -30%, which agrees well with the data. However, we cannot accommodate the CP asymmetries of $B\to ηK^*$ in our analysis, which could indicate the existence of some new CP violating sources.

hep-ph↗
arXiv2007

Expectations on $B\to (K^*_{0}(1430),K^*_{2}(1430))ϕ$ decays

As the annihilation contributions play important roles in solving the puzzle of the small longitudinal polarizations in $B\to K^* ϕ$ decays, we examine the similar effects in the decays of $B\to K^*_{0,2}(1430) ϕ$. For the calculations on the annihilated contributions, we adopt that the form factors in $B\to K^{(*)} ϕ$ decays are parameters determined by the observed branching ratios (BRs), polarization fractions (PFs) and relative angles in experiments and we connect the parameters between $B\to K^*_{0(2)} ϕ$ and $B\to K^{(*)}ϕ$ by the ansatz of correlating $\la K^*_n(1430) ϕ| (V-A)_μ|0\ra$ to $\la K^{(*)} ϕ| (V-A)_μ|0\ra$. We find that the BR of $B_d\to K^{*0}_{0}(1430) ϕ$ is $(3.69 \pm 0.47)\times 10^{-6}$. By using the transition form factors of $B\to K^*_2(1430)$ in the light-front quark model (LFQM) and the 2nd version of Isgur-Scora-Grinstein-Wise (ISGW2), we show that BR of $B_d\to K^{*0}_{2}(1430)ϕ$ is a broad allowed value and $(1.70\pm0.80)\times 10^{-6}$, respectively. In terms of the recent BABAR's observations on BRs and PFs in $B_d\to K^{*0}_{2}(1430)ϕ$, the results in the LFQM are found to be more favorable. In addition, due to the annihilation contributions to $B\to K^*_2ϕ$ and $B\to K^*ϕ$ being opposite in sign, we demonstrate that the longitudinal polarization of $B_d\to K^{*0}_2(1430) ϕ$ is always O(1) with or without including the annihilation contributions.

hep-ph↗
arXiv2007

Implications of the HyperCP Data on $B$ and $τ$ decays

If the HyperCP three events for the decay of $Σ^+\to pμ^+μ^-$ are explained by a new pseudoscalar (axial-vector) boson $X_{P(A)}$ with a mass of 214.3 MeV, we study the constraints on the couplings between $X_{P(A)}$ and fermions from the experimental data in $K$ and $B$ processes. Some implications of the new particle on flavor changing $B$ and $τ$ decays are given. Explicitly, we show that the decay branching ratios of $B_{s}\toϕX_{P(A)}\to ϕμ^{+}μ^{-}$, $B_{d}\to K_{0}^{*}(1430){P(A)}\to K_{0}^{*}(1430)μ^{+}μ^{-}$ and $τ\toμX_{P(A)}\toμμ^{+}μ^{-}$ can be as large as $2.7 (2.8)\times 10^{-6}$, $7.4 (7.5)\times 10^{-7}$ and $1.7 (0.14)\times 10^{-7}$, respectively.

hep-ph↗
arXiv2007

$η^{(\prime)}$ productions in semileptonic B decays

Inspired by the new measurements on $B^{-}\to η^{(\prime)}\ell \barν_{\ell}$ from the BaBar Collaboration, we examine the constraint on the flavor-singlet mechanism, proposed to understand the large branching ratios for $B\to η^{\prime} K$ decays. Based on the mechanism, we study the decays of $\bar B_{d,s}\to η^{(\prime)} \ell^{+} \ell^{-}$ and find that they are sensitive to the flavor-singlet effects. In particular, we show that the decay branching ratios of $\bar B_{d,s}\to η^{\prime} \ell^{+} \ell^{-}$ can be as large as $O(10^{-8})$ and $O(10^{-6})$, respectively.

hep-ph↗
arXiv2006

Charged Higgs on $B^{-} \to τ\barν_τ$ and $\bar B\to P(V) \ell \barν_{\ell}$

We study the charged Higgs effects on the decays of $B^{-} \to τ\barν_τ$ and $\bar B\to P(V) \ell \barν_{\ell}$ with $P=π^{+},D^{+}$ and $V=ρ^{+},D^{*+}$. We concentrate on the minimal supersymmetric standard model with nonholomorphic terms at a large $\tanβ$. To extract new physics contributions, we define several physical quantities related to the decay rate and angular distributions to reduce uncertainties from the QCD as well as the CKM elements. With the constraints from the recent measurement on the decay branching ratio of $B^{-} \to τ\barν_τ$, we find that the charged Higgs effects could be large and measurable.

hep-ph↗
arXiv2006

Lepton flavor violation in $τ$ decays

We study the lepton flavor violation (LFV) in tau decays in the framework of the supersymmetric seesaw mechanism with nonholomorphic terms for the lepton sector at a large $\tanβ$. In particular, we analyze two new decay modes $τ\to \ell f_0(980)$ and $τ\to \ell K^{+} K^{-}$ arising from the scalar boson exchanges contrast to $τ\to \ellη^{(\prime)}$ from the pseudoscalar ones. We find that the decay branching ratios of the two new modes could be not only as large as the current upper limits of $O(10^{-7})$, but also larger than those of $τ\to \ell η^{(\prime)}$. Experimental searches for the two modes are important for the LFV induced by the scalar-mediated mechanism. In addition, we show that the decay branching ratios of $τ\to \ell μ^{+} μ^{-}$ are related to those of $τ\to \ell η$ and $τ\to \ell f_0(980)$.

hep-ph↗
arXiv2006

Probe the effects of split SUSY in rare B decays

We study the decays of $B\to K^{(*)} \ell^{+} \ell^{-}$ in split supersymmetry with R-parity violation. We find that the decay branching ratio of $B\to Kτ^+τ^-$ in the new physics model due to the scalar interactions can be $1.8\times 10^{-6}$ which is about one order of magnitude larger that in the standard model, whereas those of $B\to K\ell^+\ell^-$ ($\ell=e$ and $μ$) and the $K^*$ modes are insensitive to the new physics. On the other hand, the forward-backward asymmetries of $B\to K τ^{+} τ^{-}$ and $Kμ^{+}μ^{-}$, vanishing in the standard model, can be over 10 and 1%, respectively. In addition, we show that the new interactions will significantly change the forward-backward asymmetry in $B\to K^* τ^{+} τ^{-}$.

hep-ph↗
arXiv2005

Factorization and polarization in two charmed-meson B decays

We provide a comprehensive test of factorization in the heavy-heavy $B$ decays motivated by the recent experimental data from BELLE and BABAR collaborations. The penguin effects are not negligible in the B decays with two pseudoscalar mesons. The direct CP asymmetries are found to be a few percent. We give estimates on the weak annihilation contributions by analogy to the observed annihilation-dominated processes. The $N_c$ insensitivity of branching ratios indicates that the soft final state interactions are not dominant. We also study the polarizations in $B\to D^*D_{(s)}^*$ decays. The power law shows that the transverse perpendicular polarization fraction is small. The effects of the heavy quark symmetry breaking caused by the perturbative QCD and power corrections on the transverse polarization are also investigated.

hep-ph↗
arXiv2005

Productions of $K^*_0(1430)$ and $K_{1}$ in B decays

We study the productions of p-wave mesons $K^*_{0}(1430)$, $K_{1}(1270)$ and $K_{1}(1400)$ in B decays. By the generalized factorization approach, we find that the branching ratios of $B\to K^*_{0}(1430) ϕ$ are similar to those of $B\to K ϕ$ while the branching ratios of $B\to K_{1}(1270) ϕ$ and $B\to K_{1}(1400) ϕ$ are $O(10^{-5})$ and $O(10^{-6})$, respectively. In terms of the observation of $B\to K_{1}(1270) γ$ by BELLE, we can remove the sign ambiguity in the mixing angle for physical states $K_1(1270)$ and $K_{1}(1400)$. In addition, we analyze annihilation contributions in the decays $B\to K_1 ϕ$ and we conclude that they could be neglected.

hep-ph↗