2,948,609 research outputs found
The purity of and challenged
It is suggested that the resonance may contain a sizeable
( in terms of the probability weight factor) four-quark component with
the up- and down- quarks and antiquarks in addition to the pair,
which component in itself has a substantial part with the isospin I=1.
Furthermore such four-quark part of the wave function should also affect the
properties of the charmonium resonance through the
mixing previously considered in the literature. It is argued that an admixture
of extra light quark pairs can explain a possible discrepancy between the
theoretical expectations and the recent data on the non- decay
width of the and the ratio of the yield of charged and neutral
meson pairs in its decays, as well as on the extra rate of the direct
decay into light hadrons and the rate of the decay . It
is further argued that the suggested four-quark component of the wave function
of the should give rise to a measurable rate of the decays
and .Comment: 13 page
Heavy quark spin symmetry breaking in near-threshold quarkonium-like resonances
A mixing of near-threshold quarkonium-like resonances with heavy
meson-antimeson pairs results in an enhancement of heavy quark spin symmetry
breaking, since the meson pairs are not eigenstates of the heavy quark spin.
The decomposition of -wave states of meson pairs in terms of the
heavy-quark-pair spin states is considered in the channel with ,
which is directly produced in annihilation. Specific processes are
suggested for experimental study of the effects of the mixing with heavy meson
pairs and of the internal spin structure of bottomonium and charmonium
resonances.Comment: 15 page
Semiclassical Calculation of Photon-Stimulated Schwinger Pair Creation
We consider the electron-positron pair creation by a photon in an external
constant electric field. The presented treatment is based on a purely
quasiclassical calculation of the imaginary part of the on-shell photon
polarization operator. By using this approach we find the pair production rate
for photons with polarization parallel as well as orthogonal to the external
electric field in the leading order in the parameter , which has
been recently found by other methods. For the orthogonal polarization we also
find a new contribution to the rate, which is leading in the ratio of the
photon energy to the electron mass . We also reproduce by a purely
geometrical calculation the exponential factor in the probability of the
stimulated pair creation at arbitrary energy of the photon.Comment: 16 pages, 4 figure
Non-factorizable terms, heavy quark masses, and semileptonic decays of D and B mesons
The non-factorizable terms in the operator product expansion have been
recognized as one of theoretical obstacles for precision determination of the
mixing parameter from semileptonic B decays. It is pointed out here
that the recent CLEO data on the parameters of the heavy quark expansion
and , combined with a theoretical bound on
strongly favor the existence of a sizeable contribution of
non-factorizable terms in semileptonic decays of mesons. Thus these terms
are likely to solve the long-standing problem of the deficit of semileptonic
decay rate of the mesons, and with better data their magnitude can be
determined and used in studies of the parameter .Comment: 7 pages, 1 figur
The Orbifold-String Theories of Permutation-Type: III. Lorentzian and Euclidean Space-Times in a Large Example
To illustrate the general results of the previous paper, we discuss here a
large concrete example of the orbifold-string theories of permutation-type. For
each of the many subexamples, we focus on evaluation of the \emph{target
space-time dimension} , the \emph{target space-time
signature} and the \emph{target space-time symmetry} of each cycle in each
twisted sector . We find in particular a gratifying \emph{space-time
symmetry enhancement} which naturally matches the space-time symmetry of each
cycle to its space-time dimension. Although the orbifolds of
-permutation-type are naturally Lorentzian, we find that the target
space-times associated to larger permutation groups can be Lorentzian,
Euclidean and even null (\hat{D}_{j}(\sigma)=0), with varying space-time
dimensions, signature and symmetry in a single orbifold.Comment: 36 page
On domain shapes and processes in supersymmetric theories
A supersymmetric theory with several scalar superfields generically has
several domain wall type classical configurations which interpolate between
various supersymmetric vacua of the scalar fields. Depending on the couplings,
some of these configurations develop instability and decay into multiple domain
walls, others can form intersections in space. These phenomena are considered
here in a simplest, yet non-trivial, model with two scalar superfields.Comment: 10 pages, LaTeX, 5 figures in LaTe
Comment on "Summing One-Loop Graphs at Multi-Particle Threshold"
The propagator of a virtual -field with emission of on-mass-shell
particles all being exactly at rest is calculated at the tree-level in theory by directly solving recursion equations for the sum of Feynman
graphs. It is shown that the generating function for these propagators is
equivalent to a Fourier transform of the recently found Green's function within
the background-field technique for summing graphs at threshold suggested by
Lowell Brown. Also the derivation of the result that the tree-level
on-mass-shell scattering amplitudes of the processes are exactly
vanishing at threshold for is thus given in the more conventional
Feynman diagram technique.Comment: 7 pages, LaTeX, TPI-MINN-92/46-
Bound States of the Heavy Flavor Vector Mesons and Y(4008) and
The and systems are studied dynamically
in the one boson exchange model, where , , , and
exchanges are taken into account. Ten allowed states with low spin
parity are considered. We suggest that the , , and
molecules should exist, and the
bound states with the same quantum numbers very likely exist as well. However,
the CP exotic (, ) and
states may not be bound by the one boson exchange potential. We find that the
I=0 configuration is more deeply bound than the I=1 configuration, hence
may not be a molecule. Although Y(4008) is
close to the threshold, the interpretation of Y(4008) as a
molecule is not favored by its huge width.
and states can be produced copiously in
annihilation, detailed scanning of the annihilation
data near the and threshold is an
important check to our predictions.Comment: 17 pages,6 figur
Presymplectic representation of bi-Hamiltonian chain
Liouville integrable systems, which have bi-Hamiltonian representation of the
Gel'fand-Zakharevich type, are considered. Bi-presymplectic representation of
one-Casimir bi-Hamiltonian chains and weakly bi-presymplectic representation of
multi-Casimir bi-Hamiltonian chains are constructed. The reduction procedure
for Poisson and presymplectic structures is presented.Comment: 17 pages, to appear in J. Phys. A: Math. Ge
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