621 research outputs found
ESC NN-Potentials in Momentum Space. I. PS-PS Exchange Potentials
A momentum space representation is derived for the Nijmegen
Extended-Soft-Core (ESC) interactions. The partial wave projection of this
representation is carried through, in principle for Two-Meson-Exchange (TME) in
general. Explicit results for the momentum space partial wave NN-potentials
from PS-PS-Exchange are given.Comment: 23 pages, 2 PostScript figures, revtex
ESC NN-Potentials in Momentum Space. II. Meson-Pair Exchange Potentials
The partial wave projection of the Nijmegen soft-core potential model for
Meson-Pair-Exchange (MPE) for NN-scattering in momentum space is presented.
Here, nucleon-nucleon momentum space MPE-potentials are NN-interactions where
either one or both nucleons contains a meson-pair vertex. Dynamically, the
meson-pair vertices can be viewed as describing in an effective way (part of)
the effects of heavy-meson exchange and meson-nucleon resonances. From the
point of view of ``duality,'' these two kinds of contribution are roughly
equivalent. Part of the MPE-vertices can be found in the chiral-invariant
phenomenological Lagrangians that have a basis in spontaneous broken chiral
symmetry. It is shown that the MPE-interactions are a very important component
of the nuclear force, which indeed enables a very succesful description of the
low and medium energy NN-data. Here we present a precise fit to the NN-data
with the extended-soft-core (ESC) model containing OBE-, PS-PS-, and
MPE-potentials. An excellent description of the NN-data for
MeV is presented and discussed. Phase shifts are given and a is reached.Comment: 27 pages, 5 PostScript figures, revtex
Neutron-star radii based on realistic nuclear interactions
The existence of neutron stars with requires the strong stiffness
of the equation of state (EoS) of neutron-star matter. We introduce a
multi-pomeron exchange potential (MPP) working universally among 3- and
4-baryons to stiffen the EoS. Its strength is restricted by analyzing the
nucleus-nucleus scattering with the G-matrix folding model. The EoSs are
derived using the Brueckner-Hartree-Fock (BHF) and the cluster variational
method (CVM) with the nuclear interactions ESC and AV18. The mass-radius
relations are derived by solving the Tolmann-Oppenheimer-Volkoff (TOV)
equation, where the maximum masses over are obtained on the basis of
the terrestrial data. Neutron-star radii at a typical mass are
predicted to be km. The uncertainty of calculated radii is
mainly from the ratio of 3- and 4-pomeron coupling constants, which cannot be
fixed by any terrestrial experiment. Though values of are not
influenced by hyperon-mixing effects, finely-observed values for them indicate
degrees of EoS softening by hyperon mixing in the region of
. If is less than about 12.4 km, the
softening of EoS by hyperon mixing has to be weak. Useful information can be
expected by the space mission NICER offering precise measurements for
neutron-star radii within .Comment: 8 pages, 7 figure
Strangeness -2 two-baryon systems
We derive strangeness -2 baryon-baryon interactions from a chiral constituent
quark model including the full set of scalar mesons. The model has been tuned
in the strangeness 0 and -1 two-baryon systems, providing parameter free
predictions for the strangeness -2 case. We calculate elastic and inelastic
and cross sections which are consistent with the
existing experimental data. We also calculate the two-body scattering lengths
for the different spin-isospin channels.Comment: 12 pages, 4 figures. Accepted for publication in Phys. Lett.
Soft-core meson-baryon interactions. II. and scattering
The potential includes the t-channel exchanges of the scalar-mesons
and f_0, vector-meson , tensor-mesons f_2 and f_2' and the
Pomeron as well as the s- and u-channel exchanges of the nucleon N and the
resonances , Roper and S_{11}. These resonances are not generated
dynamically. We consider them as, at least partially, genuine three-quark
states and we treat them in the same way as the nucleon. The latter two
resonances were needed to find the proper behavior of the phase shifts at
higher energies in the corresponding partial waves. The soft-core -model
gives an excellent fit to the empirical S- and P-wave phase shifts up
to T_{lab}=600 MeV. Also the scattering lengths have been reproduced well and
the soft-pion theorems for low-energy scattering are satisfied. The
soft-core model for the interaction is an SU_f(3)-extension of the
soft-core -model. The potential includes the t-channel exchanges
of the scalar-mesons a_0, and f_0, vector-mesons , and
, tensor-mesons a_2, f_2 and f_2' and the Pomeron as well as u-channel
exchanges of the hyperons and . The fit to the empirical S-, P- and D-wave phase shifts up to T_{lab}=600 MeV is reasonable and
certainly reflects the present state of the art. Since the various
phase shift analyses are not very consistent, also scattering observables are
compared with the soft-core -model. A good agreement for the total and
differential cross sections as well as the polarizations is found.Comment: 24 pages, 20 PostScript figures, revtex4, submitted to Phys. Rev.
Soft two-meson-exchange nucleon-nucleon potentials. I. Planar and crossed-box diagrams
Pion-meson-exchange nucleon-nucleon potentials are derived for two nucleons
in the intermediate states. The mesons we include are (i) pseudoscalar mesons:
; (ii) vector mesons: ; (iii) scalar
mesons: ; and (iv) the
contribution from the Pomeron. Strong dynamical pair suppression is assumed,
and at the nucleon-nucleon-meson vertices Gaussian form factors are
incorporated into the relativistic two-body framework using a dispersion
representation for the pion- and meson-exchange amplitudes. The Fourier
transformations are performed using factorization techniques for the energy
denominators. The potentials are first calculated in the adiabatic
approximation to all planar and crossed three-dimensional momentum-space
-meson diagrams. Next, we calculate the corrections.Comment: 28 pages RevTeX, 8 postscript figures; revised version as to appear
in Phys. Rev.
Soft-core meson-baryon interactions. I. One-hadron-exchange potentials
The Nijmegen soft-core model for the pseudoscalar-meson baryon interaction is
derived, analogous to the Nijmegen NN and YN models. The interaction
Hamiltonians are defined and the resulting amplitudes for one-meson-exchange
and one-baryon-exchange in momentum space are given for the general mass case.
The partial wave projection is carried through and explicit expressions for the
momentum space partial wave meson-baryon potentials are presented.Comment: 25 pages, 2 PostScript figures, revtex4, submitted to Phys. Rev.
Soft two-meson-exchange nucleon-nucleon potentials. II. One-pair and two-pair diagrams
Two-meson-exchange nucleon-nucleon potentials are derived where either one or
both nucleons contains a pair vertex. Physically, the meson-pair vertices are
meant to describe in an effective way (part of) the effects of heavy-meson
exchange and meson-nucleon resonances. {}From the point of view of ``duality,''
these two kinds of contribution are roughly equivalent. The various
possibilities for meson pairs coupling to the nucleon are inspired by the
chiral-invariant phenomenological Lagrangians that have appeared in the
literature. The coupling constants are fixed using the linear model.
We show that the inclusion of these two-meson exchanges gives a significant
improvement over a potential model including only the standard one-boson
exchanges.Comment: 21 pages RevTeX, 7 postscript figures; revised version as to appear
in Phys. Rev.
Soft-core hyperon-nucleon potentials
A new Nijmegen soft-core OBE potential model is presented for the low-energy
YN interactions. Besides the results for the fit to the scattering data, which
largely defines the model, we also present some applications to hypernuclear
systems using the G-matrix method. An important innovation with respect to the
original soft-core potential is the assignment of the cut-off masses for the
baryon-baryon-meson (BBM) vertices in accordance with broken SU(3), which
serves to connect the NN and the YN channels. As a novel feature, we allow for
medium strong breaking of the coupling constants, using the model with
a Gell-Mann--Okubo hypercharge breaking for the BBM coupling. We present six
hyperon-nucleon potentials which describe the available YN cross section data
equally well, but which exhibit some differences on a more detailed level. The
differences are constructed such that the models encompass a range of
scattering lengths in the and channels. For the
scalar-meson mixing angle we obtained values to 40 degrees, which
points to almost ideal mixing angles for the scalar states. The
G-matrix results indicate that the remarkably different spin-spin terms of the
six potentials appear specifically in the energy spectra of
hypernuclei.Comment: 37 pages, 4 figure
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