640 research outputs found
Vector Meson Propagator and Baryon Current Conservation
If baryons couple only with -mesons, one found the baryon spectral
function may be negative. We show this unacceptable result is caused by the
-terms in the -meson propagator. Their contribution may
not vanish in approximate calculations which violate the baryon current
conserves. A rule is suggested, by which the calculated baryon spectral
function is well behaved.Comment: 9 pages (LaTeX file), 3 figures (PostScript file
Coupled Dyson-Schwinger Equations and Effects of Self-Consistency
Using the model as an effective tool, the effects of
self-consistency are studied in some detail. A coupled set of Dyson-Schwinger
equations for the renormalized baryon and meson propagators in the model is solved self-consistently according to the dressed
Hartree-Fock scheme, where the hadron propagators in both the baryon and meson
self-energies are required to also satisfy this coupled set of equations. It is
found that the self-consistency affects the baryon spectral function
noticeably, if only the interaction with mesons is considered.
However, there is a cancellation between the effects due to the and
mesons and the additional contribution of mesons makes the
above effect insignificant. In both the and cases the
effects of self-consistency on meson spectral function are perceptible, but
they can nevertheless be taken account of without a self-consistent
calculation. Our study indicates that to include the meson propagators in the
self-consistency requirement is unnecessary and one can stop at an early step
of an iteration procedure to obtain a good approximation to the fully
self-consistent results of all the hadron propagators in the model, if an
appropriate initial input is chosen. Vertex corrections and their effects on
ghost poles are also studied.Comment: 20 pages (include 5 tables), 17 figures (PostScript file
A Comparative Study of within QCD Sum Rules with Two Typical Correlators up to Next-to-Leading Order
The B-decay constant is an important component for studying -meson
decays, which can be studied through QCD sum rules. We make a detailed
discussion on from two sum rules, i.e. sum rules I and II, which are
derived from the conventional correlator and the correlator with chiral
currents respectively. It is found that these two sum rules are consistent with
each other. However, the sum rules II has less uncertainty sources than that of
sum rules I, and then it can be more accurate if we know the dimension-four
gluon condensate well. It is found that decreases with the increment of
, and to compare with the Belle experimental data on , both sum rules
prefer smaller pole -quark mass, GeV. By varying all the
input parameters in their reasonable region and adding all the uncertainties
together in quadrature, we obtain MeV for sum rules I and
MeV for sum rules II.Comment: 11 pages, 4 figures, 2 tables. To match the printed version. To be
published in Communications in Theoretical Physic
Identifying topological edge states in 2D optical lattices using light scattering
We recently proposed in a Letter [Physical Review Letters 108 255303] a novel
scheme to detect topological edge states in an optical lattice, based on a
generalization of Bragg spectroscopy. The scope of the present article is to
provide a more detailed and pedagogical description of the system - the
Hofstadter optical lattice - and probing method. We first show the existence of
topological edge states, in an ultra-cold gas trapped in a 2D optical lattice
and subjected to a synthetic magnetic field. The remarkable robustness of the
edge states is verified for a variety of external confining potentials. Then,
we describe a specific laser probe, made from two lasers in Laguerre-Gaussian
modes, which captures unambiguous signatures of these edge states. In
particular, the resulting Bragg spectra provide the dispersion relation of the
edge states, establishing their chiral nature. In order to make the Bragg
signal experimentally detectable, we introduce a "shelving method", which
simultaneously transfers angular momentum and changes the internal atomic
state. This scheme allows to directly visualize the selected edge states on a
dark background, offering an instructive view on topological insulating phases,
not accessible in solid-state experiments.Comment: 17 pages, 10 figures. Revised and extended version, to appear in EJP
Special Topic for the special issue on "Novel Quantum Phases and Mesoscopic
Physics in Quantum Gases". Extended version of arXiv:1203.124
Top-quark couplings to TeV resonances at future lepton colliders
We study the processes and at future lepton colliders as probes of the couplings of the top quark to
resonances at the TeV scale. We consider the cases in which the dominant low
energy feature of a strongly interacting electroweak symmetry breaking sector
is either a scalar or a vector resonance with mass near 1 TeV. We find that
future lepton colliders with high energy and high luminosity have great
potential to sensitively probe these physics scenarios. In particular, at a 1.5
TeV linear collider with an integrated luminosity of 200 fb, we expect
about 120 events for either a scalar or a vector to decay to . Their leading partial decay widths, which characterize the coupling
strengths, can be statistically determined to about 10% level.Comment: 33 pages, 9 ps figures, 1 tabl
Search for lepton-flavor-violating decays at Belle
We have searched for neutrinoless lepton decays into and ,
where stands for an electron or muon, and for a vector meson
(, , , or ), using 543 fb
of data collected with the Belle detector at the KEKB asymmetric-energy
collider. No excess of signal events over the expected background has
been observed, and we set upper limits on the branching fractions in the range
at the 90% confidence level. These upper limits
include the first results for the mode as well as new limits that
are significantly more restrictive than our previous results for the , , and modes.Comment: 7 pages, 16 figure
Measurement of the ratio B(D0->pi+pi-pi0)/B(D0->K-pi+pi0) and the time-integrated CP asymmetry in D0->pi+pi-pi0
We report a high-statistics measurement of the relative branching fraction
B(D0->pi+pi-pi0)/B(D0->K-pi+pi0) using a 532 fb^{-1} data sample collected with
the Belle detector at the KEKB asymmetric-energy e+e- collider. The measured
value of the relative branching fraction is B(D0->pi+pi-pi0)/B(D0->K-pi+pi0) =
(10.12 +/- 0.04(stat) +/- 0.18(syst))x10^{-2} which has an accuracy comparable
to the world average. We also present a measurement of the time-integrated CP
asymmetry in D0->pi+pi-pi0 decay. The result, A_{CP} = (0.43 +/- 1.30)%, shows
no significant CP violation.Comment: 15 pages, 11 figures, submitted to Physics Letters
X(3872) and Other Possible Heavy Molecular States
We perform a systematic study of the possible molecular states composed of a
pair of heavy mesons such as , , in
the framework of the meson exchange model. The exchanged mesons include the
pseudoscalar, scalar and vector mesons. Through our investigation, we find that
(1) the structure X(3764) is not a molecular state; (2) There exists strong
attraction in the range fm for the system with .
If future experiments confirm as a loosely bound molecular state,
its quantum number is probably . Its partner state may
be searched for in the channel; (3) The vector meson exchange
provides strong attraction in the channel together with the
pion exchange. A bound state solution exists with a reasonable cutoff parameter
GeV. X(3872) may be accommodated as a molecular state
dynamically although drawing a very definite conclusion needs further
investigation; (4) The molecular state exists.Comment: 21 pages, 17 tables, 11 figures. Typos correcte
Shrinking a large dataset to identify variables associated with increased risk of Plasmodium falciparum infection in Western Kenya
Large datasets are often not amenable to analysis using traditional single-step approaches. Here, our general objective was to apply imputation techniques, principal component analysis (PCA), elastic net and generalized linear models to a large dataset in a systematic approach to extract the most meaningful predictors for a health outcome. We extracted predictors for Plasmodium falciparum infection, from a large covariate dataset while facing limited numbers of observations, using data from the People, Animals, and their Zoonoses (PAZ) project to demonstrate these techniques: data collected from 415 homesteads in western Kenya, contained over 1500 variables that describe the health, environment, and social factors of the humans, livestock, and the homesteads in which they reside. The wide, sparse dataset was simplified to 42 predictors of P. falciparum malaria infection and wealth rankings were produced for all homesteads. The 42 predictors make biological sense and are supported by previous studies. This systematic data-mining approach we used would make many large datasets more manageable and informative for decision-making processes and health policy prioritization
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