3,477 research outputs found
Three-body dynamics for the X(3872)
We investigate the role played by the three-body dynamics on
the near-threshold resonance X(3872) charmonium state, which is assumed to be
formed by nonperturbative dynamics. It is demonstrated that, as
compared to the naive static-pions approximation, the imaginary parts that
originate from the inclusion of dynamical pions reduce substantially the width
from the intermediate state. In particular, for a resonance
peaked at 0.5 MeV below the threshold, this contribution to
the width is reduced by about a factor of 2, and the effect of the pion
dynamics on the width grows as long as the resonance is shifted towards the
threshold. Although the physical width of the is
dominated by inelastic channels, our finding should still be of importance for
the line shapes in the channel below threshold.
For example, in the scattering length approximation, the imaginary part of the
scattering length includes effects of all the pion dynamics and does not only
stem from the width. Meanwhile, we find that another important quantity
for the phenomenology, the residue at the pole, is weakly sensitive to
dynamical pions. In particular, we find that the binding energy dependence of
this quantity from the full calculation is close to that found from a model
with pointlike interactions only, consistent with earlier claims.
Coupled-channel effects (inclusion of the charged channel) turn
out to have a moderate impact on the results.Comment: 34 pages, 6 figures, version to appear in Phys.Rev.
A remark on collisions of domain walls in a supersymmetric model
The process of collision of two parallel domain walls in a supersymmetric
model is studied both in effective Lagrangian approximation and by numerical
solving of the exact classical field problem. For small initial velocities we
find that the walls interaction looks like elastic reflection with some delay.
It is also shown that in such approximation internal parameter of the wall may
be considered as a time-dependent dynamical variable.Comment: 6 pages, LaTeX, 3 figures (eps), fig. 2 correcte
On the Extraction of Cross Sections for pi0 and eta Photoproduction off Neutrons from Deuteron Data
We discuss the procedure of extracting the photoproduction cross section for
neutral pseudoscalar mesons off neutrons from deuteron data. The main statement
is that the final-state interaction (FSI) corrections for the proton and
neutron target are in general not equal, but for pi0 production there are
special cases were they have to be identical and there are large regions in the
parameter space of incident photon energy and pion polar angle, \theta^*, where
they happen to be quite similar. The corrections for both target nucleons are
practically identical for production in the energy range of the
Delta(1232)3/2+ resonance due to the specific isospin structure of this
excitation. Also above the -isobar range large differences between
proton and neutron correction factors are only predicted for extreme forward
angles ( < 20 deg), but the results are similar for larger angles.
Numerical results for the gp-->pi0p and gn-->pi0n correction factors are
discussed. Also the model description for the available data on the
differential gd-->pi0pn cross sections are given.Comment: 16 pages, 5 figures; v2 fixed several minor typo
Level rearrangement in exotic atoms and quantum dots
A presentation and a generalisation are given of the phenomenon of level
rearrangement, which occurs when an attractive long-range potential is
supplemented by a short-range attractive potential of increasing strength. This
problem has been discovered in condensate-matter physics and has also been
studied in the physics of exotic atoms. A similar phenomenon occurs in a
situation inspired by quantum dots, where a short-range interaction is added to
an harmonic confinement.Comment: 12 pages, 11 figures, RevTeX
KKbar molecules with momentum-dependent interactions
It is shown that the momentum-dependent kaon-antikaon interactions generated
via vector meson exchange from the standard SU_V(3) x SU_A(3) interaction
Lagrangian lead to a non-local potential in coordinate space that can be
incorporated without approximation into a non-relativistic version of the
Bethe-Salpeter wave equation containing a radial-dependent effective kaon mass
appearing in a fully symmetrized kinetic energy operator, in addition to a
local potential. Estimates of the mass and decay widths of f_0(980) and
a_0(980), considered as KKbar molecules of isospin 0 and 1, as well as for
K^+K^- atomic bound states (kaonium) are presented, and compared with previous
studies of a similar nature. It is argued that without a better knowledge of
hadronic form factors it is not possible to distinguish between the molecular
versus elementary particle models for the structure of the light scalar mesons.Comment: 14 pages, 2 tables, 5 figures. Added subsection on s-channel
exchange, additional remarks on the possible effect of gluon exchange, and 1
additional figur
Reconciling the X(3872) with the near-threshold enhancement in the D^0\bar{D}^{*0} final state
We investigate the enhancement in the D^0\bar{D}^0\pi^0 final state with the
mass M=3875.2\pm 0.7^{+0.3}_{-1.6}\pm 0.8 MeV found recently by the Belle
Collaboration in the B\to K D^0\bar{D}^0\pi^0 decay and test the possibility
that this is yet another manifestation of the well-established resonance
X(3872). We perform a combined Flatte analysis of the data for the
D^0\bar{D}^0\pi^0 mode, and for the \pi^+\pi^- J/\psi mode of the X(3872). Only
if the X(3872) is a virtual state in the D^0\bar{D}^{*0} channel, the data on
the new enhancement comply with those on the X(3872). In our fits, the mass
distribution in the D^0\bar{D}^{*0} mode exhibits a peak at 2-3 MeV above the
D^0\bar{D}^{*0} threshold, with a distinctive non-Breit-Wigner shape.Comment: RevTeX4, 17 pages, some references updated and corrected, version
published in Phys. Rev.
Angular asymmetries in the reactions pp \to d\pi^+\eta and pn \to d\pi^0\eta and a_0-f_0 mixing
The reactions pp\to d\pi^+\eta and pn\to d\pi^0\eta are of special interest
for investigating the a_0(980) (J^P=0^+) resonance in the process NN \to da_0
\to d\pi\eta. We study some aspects of those reactions within a general
formalism and also in a concrete phenomenological model. In particular, it is
shown that the presence of nonresonant (i.e. without excitation of the a_0
resonance) contributions to these reactions yields nonvanishing values for
specific polarization observables, i.e. to effects like those generated by
a_0-f_0 mixing. An experimental determination of these observables for the
reaction pp\to d\pi^+\eta would provide concrete information on the magnitude
of those nonresonant contributions to \pi\eta production. We discuss also the
possibility of extracting information about a_0-f_0 mixing from the reaction pn
\to d\pi^0\eta with polarized proton beam.Comment: 14 pages, 3 figure
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