5,158 research outputs found

### Direct CP violation in two-body hadronic charmed meson decays

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
$a_{dir}^{\rm (tree)}$ at tree level can be reliably estimated. In general, it
lies in the range $10^{-4}<a_{dir}^{\rm (tree)}<10^{-3}$. Short-distance QCD
penguins and penguin annihilation are calculated using QCD factorization. Their
effects are generally small, especially for $D\to VP$ 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 $D^0\to K^+K^-$
and $D^0\to \pi^+\pi^-$ in which $a_{dir}^{\rm (tree)}$ is absent. The maximal
$\Delta a_{CP}^{\rm dir}$, the direct CP asymmetry difference between the
above-mentioned two modes, allowed in the SM is around -0.25%, more than
$2\sigma$ away from the current world average of $-(0.645\pm 0.180)%$.Comment: 19 pages, 2 figures; typos correcte

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

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 $W$-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

Hadronic decay modes $D^0\to(\bar K^0, \bar K^{*0})\eta,\eta'$ and
$(D^+,D_s^+)\to(\pi^+,\rho^+)\eta,\eta'$ are studied in the generalized
factorization approach. Form factors for $(D,D_s^+)\to(\eta,\eta')$ 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 $D^0\to\bar K^0\eta', D^+\to\pi^+\eta$ and
$D_s^+\to\rho^+\eta'$; the calculated decay rates for the first two decay modes
are too small by an order of magnitude. We show that the weak decays $D^0\to
K^-\pi^+$ and $D^+\to K^+\bar K^0$ followed by resonance-induced final-state
interactions (FSI), which are amenable technically, are able to enhance the
branching ratios of $D^0\to\bar K^0\eta'$ and $D^+\to\pi^+\eta$ dramatically
without affecting the agreement between theory and experiment for $D^0\to\bar
K^0\eta$ and $D^+\to\pi^+\eta'$. We argue that it is difficult to understand
the observed large decay rates of $D_s^+\to \rho^+\eta'$ and $\rho^+\eta$
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 $D_s^+\to\rho^+ \eta'$
and $D_s^+\to\eta' e^+\nu$ 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

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 $D$ 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 $D$. The factorial moments of the negative
binomial distribution can be obtained exactly in the limit as $D$ 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 $B \to PP$ and $PV$ decays

Using flavor SU(3) symmetry, we perform a model-independent analysis of
charmless $\bar B_{u,d} (\bar B_s) \to PP, ~PV$ 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 $\bar B_s \to PV$ and $\bar B_d \to PV$.Comment: 47 pages, 3 figures, 28 table

### Quantum Convolutional Error Correcting Codes

I report two general methods to construct quantum convolutional codes for
$N$-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

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

Cabibbo-allowed nonleptonic weak decays of charmed baryons
\lamc,~\xin,~\xip and $\Omega_c^0$ into an octet baryon and a pseudoscalar
meson are analyzed. The nonfactorizable contributions are evaluated under pole
approximation, and it turns out that the $s$-wave amplitudes are dominated by
the low-lying \halfm resonances, while $p$-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) $s$ waves are no longer dominated by commutator terms; the
current-algebra method is certainly not applicable to parity-violating
amplitudes, (ii) nonfactorizable $W$ 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-$N_c$ 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 $\alpha$ asymmetry parameter of certain proposed decay
modes will help discern various models; especially the sign of $\alpha$ in
\lamc\ri\Sigma\pi decays can be used to unambiguously differentiate recent
theoretical schemes from current algebra, and (v) $p$ 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.

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)

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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