3,411 research outputs found
Q-complements on log surfaces
In this paper the log surfaces without \QQ-complement are classified. In
particular, they are non-rational always. This result takes off the restriction
in the theory of complements and allows one to apply it in the most wide class
of log surfaces.Comment: Latex2e, 3 page
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.
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.
Insights on scalar mesons from their radiative decays
We estimate the rates for radiative transitions of the lightest scalar mesons
f_0(980) and a_0(980) to the vector mesons rho and omega. We argue that
measurements of the radiative decays of those scalar mesons can provide
important new information on their structure.Comment: 20 pages, 5 figures; appendix added, to be 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
Residual stress management in welding: measurement, fatigue analysis and improvement treatments
Residual stress (RS) management is a concept according to which three major stages, i.e. RS determination, RS fatigue analysis
and RS beneficial redistribution are considered and evaluated, either experimentally or theoretically to achieve the optimum
performance of welded structures. All three stages as well as a number of new engineering tools such as ultrasonic computerized
complex for residual stress measurement, UltraMARS, software for analysis of the effect of residual stresses on the fatigue life of
welded elements, ReSIsT, and new technology and, based on it, compact system for beneficial redistribution of residual stresses
by ultrasonic impact treatment, UltraPeen, will be discussed. Examples of industrial applications of the developed engineering
tools for residual stress analysis and fatigue life improvement of welded elements and structures will be given
The Laser Ion Source Trap (LIST) coupled to a gas cell catcher
The proof of principle of the Laser Ion Source Trap (LIST) coupled to a gas
cell catcher system has been demonstrated at the Leuven Isotope Separator
On-Line (LISOL). The experiments were carried out by using the modified gas
cell-based laser ion source and the SextuPole Ion Guide (SPIG). Element
selective resonance laser ionization of neutral atoms was taking place inside
the cold jet expanding out of the gas cell catcher. The laser path was oriented
in longitudinal as well as transverse geometries with respect to the atoms
flow. The enhancement of beam purity and the feasibility for in-source laser
spectroscopy were investigated in off-line and on-line conditions.Comment: 11 pages, 13 figure
Two-photon decays of hadronic molecules
In many calculations of the two--photon decay of hadronic molecules, the
decay matrix element is estimated using the wave function at the origin
prescription, in analogy to the two-photon decay of parapositronium. We
question the applicability of this procedure to the two-photon decay of
hadronic molecules for it introduces an uncontrolled model dependence into the
calculation. As an alternative approach, we propose an explicit evaluation of
the hadron loop. For shallow bound states, this can be done as an expansion in
powers of the range of the molecule binding force. In the leading order one
gets the well-known point-like limit answer. We estimate, in a self-consistent
and gauge invariant way, the leading range corrections for the two-photon decay
width of weakly bound hadronic molecules emerging from kaon loops. We find them
to be small. The role of possible short-ranged operators and of the width of
the scalars remains to be investigated.Comment: LaTeX2e, 26 pages, new figure and additional appendix added, version
to appear in Phys.Rev.
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