22 research outputs found
Meson exchange model for pseudoscalar meson-meson scattering
A dynamical model for pseudoscalar-pseudoscalar meson scattering based on meson exchange, suitable for use in a variety of low- and intermediate-energy mesonic interactions, has been constructed and applied to ππ and kπ scattering with good quantitative results. The model includes both s- and t-channel exchange, and is found to require pseudoscalar-pseudoscalar coupling to a scalar octet to fit the high energy s-wave phases in the I = 0 ππ channel and in the channel. Coupling of the ππ and KK̄ channels is found to play a crucial role in explaining the S∗(975) resonanc
Role of correlated two-pion exchange in scattering
A dynamical model for S-- and P--wave correlated (and )
exchange between a kaon and a nucleon is presented, starting from corresponding
amplitudes in the pseudophysical region, which
have been constructed from nucleon, --isobar and hyperon (,
) exchange Born terms and a realistic meson exchange model of the and amplitude. The
contribution in the s--channel is then obtained by performing a dispersion
relation over the unitarity cut. In the --channel, considerable
ambiguities exist, depending on how the dispersion integral is performed. Our
model, supplemented by short range interaction terms, is able to describe
empirical data below pion production threshold in a satisfactory way.Comment: 24 pages, REVTEX, figures available from the author
The twin paradox and Mach's principle
The problem of absolute motion in the context of the twin paradox is
discussed. It is shown that the various versions of the clock paradox feature
some aspects which Mach might have been appreciated. However, the ultimate
cause of the behavior of the clocks must be attributed to the autonomous status
of spacetime, thereby proving the relational program advocated by Mach as
impracticable.Comment: Latex2e, 11 pages, 6 figures, 33 references, no tables. Accepted for
publication in The European Physical Journal PLUS (EPJ PLUS
Friedel Oscillations in Relativistic Nuclear Matter
We calculate the low-momentum N-N effective potential obtained in the OBE
approximation, inside a nuclear plasma at finite temperature, as described by
the relativistic - model. We analyze the screening effects
on the attractive part of the potential in the intermediate range as density or
temperature increase. In the long range the potential shows Friedel-like
oscillations instead of the usual exponential damping. These oscillations arise
from the sharp edge of the Fermi surface and should be encountered in any
realistic model of nuclear matter.Comment: 11 pages in preprint format, typeset using REVTEX, 3 included figures
in tar, compressed, uuencoded forma
Unitarity and the Bethe-Salpeter Equation
We investigate the relation between different three-dimensional reductions of
the Bethe-Salpeter equation and the analytic structure of the resultant
amplitudes in the energy plane. This correlation is studied for both the
interaction Lagrangian and the system with -, -,
and -channel pole diagrams as driving terms. We observe that the equal-time
equation, which includes some of the three-body unitarity cuts, gives the best
agreement with the Bethe-Salpeter result. This is followed by other 3-D
approximations that have less of the analytic structure.Comment: 17 pages, 8 figures; RevTeX. Version accepted for publication in
Phys. Rev.
Composite vertices that lead to soft form factors
The momentum-space cut-off parameter of hadronic vertex functions
is studied in this paper. We use a composite model where we can measure the
contributions of intermediate particle propagations to . We show that
in many cases a composite vertex function has a much smaller cut-off than its
constituent vertices, particularly when light constituents such as pions are
present in the intermediate state. This suggests that composite
meson-baryon-baryon vertex functions are rather soft, i.e., they have \Lambda
considerably less than 1 GeV. We discuss the origin of this softening of form
factors as well as the implications of our findings on the modeling of nuclear
reactions.Comment: REVTex, 19 pages, 5 figs(to be provided on request
pi-NN Coupling Constants from NN Elastic Data between 210 and 800 Mev
High partial waves for and elastic scattering are examined
critically from 210 to 800 MeV. Non-OPE contributions are compared with
predictions from theory. There are some discrepancies, but sufficient agreement
that values of the coupling constants for exchange
and for charged exchange can be derived. Results are and , where the first error is statistical and the
second is an estimate of the likely systematic error, arising mostly from
uncertainties in the normalisation of total cross sections and
.Comment: 21 pages of LaTeX, UI-NTH-940
Role of baryonic resonances in the dilepton emission in nucleon-nucleon collisions
Within an effective Lagrangian model, we present calculations for cross
sections of the dilepton production in proton-proton and proton-neutron
collisions at laboratory kinetic energies in 1-5 GeV range. Production
amplitudes include contributions from the nucleon-nucleon bremsstrahlung as
well as from the mechanism of excitation, propagation, and radiative decay of
Delta(1232) and N*(1520) intermediate baryonic resonances. It is found that the
delta isobar terms dominate the cross sections in the entire considered beam
energy range. Our calculations are able to explain the data of the DLS
collaboration on the dilepton production in proton-proton collisions for beam
energies below 1.3 GeV. However, for incident energies higher than this the
inclusion of contributions from other dilepton sources like Dalitz decay of pi0
and eta mesons, and direct decay of rho and omega mesons is necessary to
describe the data.Comment: 22 pages, 7 figures, more details of the calculations added, version
to appear in Phys. Rev
Vector meson production and nucleon resonance analysis in a coupled-channel approach for energies m_N < sqrt(s) < 2 GeV I: pion-induced results and hadronic parameters
We present a nucleon resonance analysis by simultaneously considering all
pion- and photon-induced experimental data on the final states gamma N, pi N, 2
pi N, eta N, K Lambda, K Sigma, and omega N for energies from the nucleon mass
up to sqrt(s) = 2 GeV. In this analysis we find strong evidence for the
resonances P_{31}(1750), P_{13}(1900), P_{33}(1920), and D_{13}(1950). The
omega N production mechanism is dominated by large P_{11}(1710) and
P_{13}(1900) contributions. In this first part, we present the results of the
pion-induced reactions and the extracted resonance and background properties
with emphasis on the difference between global and purely hadronic fits.Comment: 54 pages, 26 figures, discussion extended, typos corrected,
references updated, to appear in Phys. Rev.
-meson production in proton-proton collisions
The production of -mesons in proton-proton collisions is investigated
within a relativistic meson-exchange model of hadronic interactions. The
experimental prerequisites for extracting the coupling strength from
this reaction are discussed. In the absence of a sufficient set of data, which
would enable an accurate determination of the coupling strength, we
perform a combined analysis, based on some reasonable assumptions, of the
existing data for both - and -meson production. We find that the
recent data from the DISTO collaboration on the angular distribution of the
meson indicate that the coupling constant is small. The
analysis yields values for that are compatible with the OZI rule.Comment: 21 pages, 3 figures, submitted to Phys.Rev.