5,158 research outputs found

    Direct CP violation in two-body hadronic charmed meson decays

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    Motivated by the recent observation of CP violation in the charm sector by LHCb, we study direct CP asymmetries in the standard model (SM) for the singly Cabibbo-suppressed two-body hadronic decays of charmed mesons using the topological-diagram approach. In this approach, the magnitude and the phase of topological weak annihilation amplitudes which arise mainly from final-state rescattering can be extracted from the data. Consequently, direct CP asymmetry adir(tree)a_{dir}^{\rm (tree)} at tree level can be reliably estimated. In general, it lies in the range 104<adir(tree)<10310^{-4}<a_{dir}^{\rm (tree)}<10^{-3}. Short-distance QCD penguins and penguin annihilation are calculated using QCD factorization. Their effects are generally small, especially for DVPD\to VP modes. Since weak penguin annihilation receives long-distance contributions from the color-allowed tree amplitude followed by final-state rescattering, it is expected to give the dominant contribution to the direct CP violation in the decays D0K+KD^0\to K^+K^- and D0π+πD^0\to \pi^+\pi^- in which adir(tree)a_{dir}^{\rm (tree)} is absent. The maximal ΔaCPdir\Delta a_{CP}^{\rm dir}, the direct CP asymmetry difference between the above-mentioned two modes, allowed in the SM is around -0.25%, more than 2σ2\sigma away from the current world average of (0.645±0.180)-(0.645\pm 0.180)%.Comment: 19 pages, 2 figures; typos correcte

    Analysis of Two-Body Decays of Charmed Baryons Using the Quark-Diagram Scheme

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    We give a general formulation of the quark-diagram scheme for the nonleptonic weak decays of baryons. We apply it to all the decays of the antitriplet and sextet charmed baryons and express their decay amplitudes in terms of the quark-diagram amplitudes. We have also given parametrizations for the effects of final-state interactions. For SU(3) violation effects, we only parametrize those in the horizontal WW-loop quark diagrams whose contributions are solely due to SU(3)-violation effects. In the absence of all these effects, there are many relations among various decay modes. Some of the relations are valid even in the presence of final-state interactions when each decay amplitude in the relation contains only a single phase shift. All these relations provide useful frameworks to compare with future experiments and to find out the effects of final-state interactions and SU(3) symmetry violations.Comment: 28 pages, 20 Tables in landscape form, 4 figures. Main changes are: (i) some errors in the Tables and in the relations between the quark-diagram amplitudes of this paper and those of Ref.[10] are corrected, (ii) improvements are made in the presentation so that comparisons with previous works and what have been done to include SU(3) breaking and final-state interactions are more clearly stated; to appear in the Physical Review

    Exclusive Hadronic D Decays to eta' and eta

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    Hadronic decay modes D0(Kˉ0,Kˉ0)η,ηD^0\to(\bar K^0, \bar K^{*0})\eta,\eta' and (D+,Ds+)(π+,ρ+)η,η(D^+,D_s^+)\to(\pi^+,\rho^+)\eta,\eta' are studied in the generalized factorization approach. Form factors for (D,Ds+)(η,η)(D,D_s^+)\to(\eta,\eta') transitions are carefully evaluated by taking into account the wave function normalization of the eta and eta'. The predicted branching ratios are generally in agreement with experiment except for D0Kˉ0η,D+π+ηD^0\to\bar K^0\eta', D^+\to\pi^+\eta and Ds+ρ+ηD_s^+\to\rho^+\eta'; the calculated decay rates for the first two decay modes are too small by an order of magnitude. We show that the weak decays D0Kπ+D^0\to K^-\pi^+ and D+K+Kˉ0D^+\to K^+\bar K^0 followed by resonance-induced final-state interactions (FSI), which are amenable technically, are able to enhance the branching ratios of D0Kˉ0ηD^0\to\bar K^0\eta' and D+π+ηD^+\to\pi^+\eta dramatically without affecting the agreement between theory and experiment for D0Kˉ0ηD^0\to\bar K^0\eta and D+π+ηD^+\to\pi^+\eta'. We argue that it is difficult to understand the observed large decay rates of Ds+ρ+ηD_s^+\to \rho^+\eta' and ρ+η\rho^+\eta simultaneously; FSI, W-annihilation and the production of excess eta' from gluons are not helpful in this regard. The large discrepancy between the factorization hypothesis and experiment for the ratio of Ds+ρ+ηD_s^+\to\rho^+ \eta' and Ds+ηe+νD_s^+\to\eta' e^+\nu remains as an enigma.Comment: 15 pages, 1 figure, to appear in Phys. Rev. D. Form factors for D to eta and eta' transitions are slightly change

    Factorial Moments in a Generalized Lattice Gas Model

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    We construct a simple multicomponent lattice gas model in one dimension in which each site can either be empty or occupied by at most one particle of any one of DD species. Particles interact with a nearest neighbor interaction which depends on the species involved. This model is capable of reproducing the relations between factorial moments observed in high--energy scattering experiments for moderate values of DD. The factorial moments of the negative binomial distribution can be obtained exactly in the limit as DD becomes large, and two suitable prescriptions involving randomly drawn nearest neighbor interactions are given. These results indicate the need for considerable care in any attempt to extract information regarding possible critical phenomena from empirical factorial moments.Comment: 15 pages + 1 figure (appended as postscript file), REVTEX 3.0, NORDITA preprint 93/4

    Flavor SU(3) symmetry and QCD factorization in BPPB \to PP and PVPV decays

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    Using flavor SU(3) symmetry, we perform a model-independent analysis of charmless Bˉu,d(Bˉs)PP, PV\bar B_{u,d} (\bar B_s) \to PP, ~PV decays. All the relevant topological diagrams, including the presumably subleading diagrams, such as the QCD- and EW-penguin exchange diagrams and flavor-singlet weak annihilation ones, are introduced. Indeed, the QCD-penguin exchange diagram turns out to be important in understanding the data for penguin-dominated decay modes. In this work we make efforts to bridge the (model-independent but less quantitative) topological diagram or flavor SU(3) approach and the (quantitative but somewhat model-dependent) QCD factorization (QCDF) approach in these decays, by explicitly showing how to translate each flavor SU(3) amplitude into the corresponding terms in the QCDF framework. After estimating each flavor SU(3) amplitude numerically using QCDF, we discuss various physical consequences, including SU(3) breaking effects and some useful SU(3) relations among decay amplitudes of BˉsPV\bar B_s \to PV and BˉdPV\bar B_d \to PV.Comment: 47 pages, 3 figures, 28 table

    Quantum Convolutional Error Correcting Codes

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    I report two general methods to construct quantum convolutional codes for NN-state quantum systems. Using these general methods, I construct a quantum convolutional code of rate 1/4, which can correct one quantum error for every eight consecutive quantum registers.Comment: Minor revisions and clarifications. To appear in Phys. Rev.

    Increased brain activation in motor cortex after acupuncture treatment for motor recovery in chronic stroke patients

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    Acupuncture has historically been recommended as adjunctive treatment to patients with stroke, but its effectiveness has yet to be proven. This case series aims to report the results of using functional magnetic resonance imaging (fMRI), together with motor function evaluations, to assess the effect of acupuncture on stable patients after stroke. Eleven chronic stroke patients underwent fMRI and motor function evaluations of their impaired upper limb before and after an 8-week period of acupuncture on two acupoints (Hegu LI-4 and Quchi LI-11), without undergoing simultaneous rehabilitation. Improvements in motor functions of the impaired upper limb were found after acupuncture treatment. Changes in cortical activities were closely related to the finding of improved motor functions. A larger and stronger activation was found in the sensorimotor area of the lesioned hemisphere after receiving the acupuncture intervention. Conjunction analysis demonstrated common regions that were activated during either motor task or acupuncture stimulation. Acupuncture may improve functions of the impaired upper limb in chronic stroke patients via modulating peri-infarct regions that are responsible for plasticity of the motor cortex

    Cabibbo-allowed nonleptonic weak decays of charmed baryons

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    Cabibbo-allowed nonleptonic weak decays of charmed baryons \lamc,~\xin,~\xip and Ωc0\Omega_c^0 into an octet baryon and a pseudoscalar meson are analyzed. The nonfactorizable contributions are evaluated under pole approximation, and it turns out that the ss-wave amplitudes are dominated by the low-lying \halfm resonances, while pp-wave ones governed by the ground-state \halfp poles. The MIT bag model is employed to calculate the coupling constants, form factors and baryon matrix elements. Our conclusions are: (i) ss waves are no longer dominated by commutator terms; the current-algebra method is certainly not applicable to parity-violating amplitudes, (ii) nonfactorizable WW exchange effects are generally important; they can be comparable to and somtimes even dominate over factorizable contributions, depending on the decay modes under consideration, (iii) large-NcN_c approximation for factorizable amplitudes also works in the heavy baryon sector and it accounts for the color nonsuppression of \lamc\ri p\bar{K}^0 relative to \lamc\ri\Lambda\pi^+, (iv) a measurement of the decay rate and the sign of the α\alpha asymmetry parameter of certain proposed decay modes will help discern various models; especially the sign of α\alpha in \lamc\ri\Sigma\pi decays can be used to unambiguously differentiate recent theoretical schemes from current algebra, and (v) pp waves are the dominant contributions to the decays \lamc\ri\Xi^0 K^+ and \xin\ri\Sigma^+ K^-, but they are subject to a large cancellation; this renders present theoretical predictions on these two channels unreliable.Comment: PHYZZX, 31 pages, 3 tables, IP-ASTP-10-93, ITP-SB-93-2

    Prediction of GABARAP interaction with the GABA type A receptor.

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    We have performed docking simulations on GABARAP interacting with the GABA type A receptor using SwarmDock. We have also used a novel method to study hydration sites on the surface of these two proteins; this method identifies regions around proteins where desolvation is relatively easy, and these are possible locations where proteins can bind each other. There is a high degree of consistency between the predictions of these two methods. Moreover, we have also identified binding sites on GABARAP for other proteins, and listed possible binding sites for as yet unknown proteins on both GABARAP and the GABA type A receptor intracellular domain

    Nonleptonic Two-Body Decays of D Mesons in Broken SU(3)

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    Decays of the D mesons to two pseudoscalars, to two vectors, and to pseudoscalar plus vector are discussed in the context of broken flavor SU(3). A few assumptions are used to reduce the number of parameters. Amplitudes are fit to the available data, and predictions of branching ratios for unmeasured modes are made.Comment: LaTeX, 24 page
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