1,052,818 research outputs found
Double charmonium production in exclusive bottomonia decays
This paper is devoted to the leading twist exclusive bottomonia decays with
double charmonium in the final state. Using models of the twist-2 charmonia
distribution amplitudes the widths of these decays are calculated within light
cone formalism. In addition, the processes under consideration are studied
within nonrelativistic QCD. In our analysis we have found that the production
of some of the -wave charmonia mesons with is allowed already
at the leading twist approximation. This means that the selection rules which
predict the suppression of such decays are violated. The mechanism which lies
behind this violation is discussed.Comment: Minor changes, some references adde
Light Cone Sum Rules for gamma* N -> Delta Transition Form Factors
A theoretical framework is suggested for the calculation of gamma* N -> Delta
transition form factors using the light-cone sum rule approach. Leading-order
sum rules are derived and compared with the existing experimental data. We find
that the transition form factors in a several GeV region are dominated by the
``soft'' contributions that can be thought of as overlap integrals of the
valence components of the hadron wave functions. The ``minus'' components of
the quark fields contribute significantly to the result, which can be
reinterpreted as large contributions of the quark orbital angular momentumComment: 38 pages, 10 figures; some typos fixed and references added, to
appear in Phys. Rev.
Comment on "Polarizability of the pion: No conflict between dispersion theory and chiral perturbation theory"
The statement of the authors of the article Phys. Rev. C 77, 065211 (2008)
that spurious singularities occur in the dispersion relation approach, where
imaginary parts of the amplitudes of the process \gamma\gamma->\pi\pi are
saturated by the contributions of meson resonances by using Breit-Wigner
expressions, is analyzed. It is shown that there are no any additional
singularities in this approach and the disagreement between the predictions of
the dispersion relations and the chiral perturbation theory for
(\alpha_1-\beta_1)_\pi^{\pm} remains.Comment: 3 pages, final version appeared in Phys. Rev.
Effect of angular momentum distribution on gravitational loss-cone instability in stellar clusters around massive BH
Small perturbations in spherical and thin disk stellar clusters surrounding
massive a black hole are studied. Due to the black hole, stars with
sufficiently low angular momentum escape from the system through the loss cone.
We show that stability properties of spherical clusters crucially depend on
whether the distribution of stars is monotonic or non-monotonic in angular
momentum. It turns out that only non-monotonic distributions can be unstable.
At the same time the instability in disk clusters is possible for both types of
distributions.Comment: 14 pages, 7 figures, submitted to MNRA
Partial widths for the decays eta(1295) -> gamma gamma and eta(1440) -> gamma gamma
We discuss gamma gamma partial widths of pseudoscalar/isoscalar mesons eta(M)
in the mass region M = 1000-1500 MeV. The transition amplitudes eta(1295) ->
gamma gamma and eta(1440) -> gamma gamma are studied within an assumption that
the decaying mesons are the members of the first radial excitation nonet 2^1S_0
q\bar q. The calculations show that partial widths being of the order of 0.1
keV are dominantly due to the n\bar n meson component while the contribution of
the s\bar s component is small.Comment: 3 pages, LaTeX, 4 EPS figures, epsfig.st
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