14,087 research outputs found
Kaon and pion parton distribution amplitudes to twist-three
We compute all kaon and pion parton distribution amplitudes (PDAs) to
twist-three and find that only the pseudotensor PDA can reasonably be
approximated by its conformal limit expression. At terrestrially accessible
energy scales, the twist-two and pseudoscalar twist-three PDAs differ
significantly from those functions commonly associated with their forms in
QCD's conformal limit. In all amplitudes studied, SU(3) flavour-symmetry
breaking is typically a 13% effect. This scale is determined by nonperturbative
dynamics; namely, the current-quark-mass dependence of dynamical chiral
symmetry breaking. The heavier-quark is favoured by this distortion, for
example, support is shifted to the s-quark in the negative kaon. It appears,
therefore, that at energy scales accessible with existing and foreseeable
facilities, one may obtain reliable expectations for experimental outcomes by
using these "strongly dressed" PDAs in formulae for hard exclusive processes.
Following this procedure, any discrepancies between experiment and theory will
be significantly smaller than those produced by using the conformal-limit PDAs.
Moreover, the magnitude of any disagreement will either be a better estimate of
higher-order, higher-twist effects or provide more realistic constraints on the
Standard Model.Comment: 14 pages, 4 figures, 2 tables. arXiv admin note: text overlap with
arXiv:1406.335
Flavour symmetry breaking in the kaon parton distribution amplitude
We compute the kaon's valence-quark (twist-two parton) distribution amplitude
(PDA) by projecting its Poincare'-covariant Bethe-Salpeter wave-function onto
the light-front. At a scale \zeta=2GeV, the PDA is a broad, concave and
asymmetric function, whose peak is shifted 12-16% away from its position in
QCD's conformal limit. These features are a clear expression of
SU(3)-flavour-symmetry breaking. They show that the heavier quark in the kaon
carries more of the bound-state's momentum than the lighter quark and also that
emergent phenomena in QCD modulate the magnitude of flavour-symmetry breaking:
it is markedly smaller than one might expect based on the difference between
light-quark current masses. Our results add to a body of evidence which
indicates that at any energy scale accessible with existing or foreseeable
facilities, a reliable guide to the interpretation of experiment requires the
use of such nonperturbatively broadened PDAs in leading-order, leading-twist
formulae for hard exclusive processes instead of the asymptotic PDA associated
with QCD's conformal limit. We illustrate this via the ratio of kaon and pion
electromagnetic form factors: using our nonperturbative PDAs in the appropriate
formulae, at spacelike-, which compares
satisfactorily with the value of inferred in annihilation
at .Comment: 7 pages, 2 figures, 3 table
Robust Preparation of GHZ and W States of Three Distant Atoms
Schemes to generate Greenberger-Horne-Zeilinger(GHZ) and W states of three
distant atoms are proposed in this paper. The schemes use the effects of
quantum statistics of indistinguishable photons emitted by the atoms inside
optical cavities. The advantages of the schemes are their robustness against
detection inefficiency and asynchronous emission of the photons. Moreover, in
Lamb-Dicke limit, the schemes do not require simultaneous click of the
detectors, this makes the schemes more realizable in experiments.Comment: 5 pages, 1 fiure. Phys. Rev. A 75, 044301 (2007
Geometric Photon-Drag Effect and Nonlinear Shift Current in Centrosymmetric Crystals
The nonlinear shift current, also known as the bulk photovoltaic current generated by linearly polarized light, has long been known to be absent in crystals with inversion symmetry. Here we argue that a nonzero shift current in centrosymmetric crystals can be activated by a photon-drag effect. Photon-drag shift current proceeds from a "shift current dipole" (a geometric quantity characterizing interband transitions) and manifests a purely transverse response in centrosymmetric crystals. This transverse nature proceeds directly from the shift-vector's pseudovector nature under mirror operation and underscores its intrinsic geometric origin. Photon-drag shift current can be greatly enhanced by coupling to polaritons and provides a new and sensitive tool to interrogate the subtle interband coherences of materials with inversion symmetry previously thought to be inaccessible via photocurrent probes
Decays of the Meson to a -Wave Charmonium State or
The semileptonic decays,
, and the two-body
nonleptonic decays, , (here and
denote and respectively, and
indicates a meson) were computed. All of the form factors appearing in the
relevant weak-current matrix elements with as its initial state and a
-wave charmonium state as its final state for the decays were precisely
formulated in terms of two independent overlapping-integrations of the
wave-functions of and the -wave charmonium and with proper kinematics
factors being `accompanied'. We found that the decays are quite sizable, so
they may be accessible in Run-II at Tevatron and in the foreseen future at LHC,
particularly, when BTeV and LHCB, the special detectors for B-physics, are
borne in mind. In addition, we also pointed out that the decays may potentially be used as a fresh window to look for the
charmonium state, and the cascade decays,
() with one of the radiative decays
being followed accordingly, may affect
the observations of meson through the decays () substantially.Comment: 24 pages, 3 figures, the replacement for improving the presentation
and adding reference
The Narrow Pentaquark As The First Non-planar Hadron With the Diamond Structure And Negative Parity
Using the picture of the flux tube model, we propose that the
pentaquark as the first candidate of the three-dimensional non-planar hadron
with the extremely stable diamond structure. The up and down quarks lie at the
corners of the diamond while the anti-strange quark sits in the center. Various
un-excited color flux tubes between the five quarks bind them into a stable and
narrow color-singlet. Such a configuration allows the lowest state having the
negative parity naturally. The decay of the pentaquark into the
nucleon and kaon requires the breakup of the non-planar diamond configuration
into two conventional planar hadrons, which involves some kind of structural
phase transition as in the condensed matter physics. Hence the width of the
pentaquark should be narrow despite that it lies above the kaon
nucleon threshold. We suggest that future lattice QCD calculation adopt
non-planar interpolating currents to explore the underlying structure of the
pentaquark
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