3,623 research outputs found

### 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 $T_{Lab} \leq 350$
MeV is presented and discussed. Phase shifts are given and a $\chi^2_{p.d.p.} =
1.15$ is reached.Comment: 27 pages, 5 PostScript figures, revtex

### 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

### Heavy flavour mass corrections to the longitudinal and transverse cross sections in e^+e^- - collisions

The sentence, 7th line below Eq. (28), starting with "Further we exclude all
interference terms ...." is wrong and has been corrected. Eq. (33) :
f_k^{l,(i)} -> h_k^{l,(i)} i=0,1 Second line below Eq. (33) m_bar(m)=m is
replaced by m_bar(\mu_0)=\mu_0 with \mu_0=4.10 GeV and \mu_0=166.1 GeV for
bottom and top respectively. The numbers in the third column of tables 1 and 2
are a little bit changed.Comment: 8 pages Latex, all compressed by uufile

### Soft-core baryon-baryon potentials for the complete baryon octet

SU(3) symmetry relations on the recently constructed hyperon-nucleon
potentials are used to develop potential models for all possible baryon-baryon
interaction channels. The main focus is on the interaction channels with total
strangeness S=-2, -3, and -4, for which no experimental data exist yet. The
potential models for these channels are based on SU(3) extensions of potential
models for the S=0 and S=-1 sectors, which are fitted to experimental data.
Although the SU(3) symmetry is not taken to be exact, the S=0 and S=-1 sectors
still provide the necessary constraints to fix all free parameters. The
potentials for the S=-2, -3, and -4 sectors, therefore, do not contain any
additional free parameters, which makes them the first models of this kind.
Various properties of the potentials are illustrated by giving results for
scattering lengths, bound states, and total cross sections.Comment: 22 pages RevTex, 6 postscript figure

### Fully double-logarithm-resummed cross sections

We calculate the complete double logarithmic contribution to cross sections
for semi-inclusive hadron production in the modified minimal-subtraction scheme
by applying dimensional regularization to the double logarithm approximation.
The full double logarithmic contribution to the coefficient functions for
inclusive hadron production in electron-positron annihilation is obtained in
this scheme for the first time. Our result agrees with all fixed order results
in the literature, which extend to next-next-to-leading order.Comment: To appear in Nuclear Physics

### Couples’ decisions on having a first child

We investigate the decision-making process of having a first child, using theories on individualisation, lifestyle choices and negotiating partnerships as a starting point. We compare couples who had their first child at a relatively young age with those who had their first child at an older than average age, using data from semi-structured interviews with 33 couples, selected from the Netherlands Kinship Panel Study (NKPS). Although expecting more explicit decision-making among older parents, our qualitative analyses show that decision-making preceding both early and postponed first childbirth is often implicit. Disagreement between partners does not necessarily lead to discussion. Factors that result in the postponement of childbearing, such as higher education, do not always play a conscious role in people’s decision-making processes.couple decision-making, early parenthood, first birth, Netherlands, postponement of family formation, qualitative analysis

### Pion-Nucleon Scattering in Kadyshevsky Formalism: II Baryon Exchange Sector

In this paper, which is the second part in a series of two, we construct tree
level baryon exchange and resonance amplitudes for $\pi N$ / $MB$-scattering in
the framework of the Kadyshevsky formalism. We use this formalism to formally
implement absolute pair suppression, where we make use of the method of
Takahashi and Umezawa. The resulting amplitudes are Lorentz invariant and
causal. We continue studying the frame dependence of the Kadyshevsky integral
equation using the method of Gross and Jackiw. The invariant amplitudes,
including those for meson exchange, are linked to the phase-shifts using the
partial wave basis.Comment: 49 page

### The geometry of whips

In this paper we study geometric aspects of the space of arcs parametrized by
unit speed in the $L^2$ metric. Physically this corresponds to the motion of a
whip, and it also arises in studying shape recognition. The geodesic equation
is the nonlinear, nonlocal wave equation $\eta_{tt} = \partial_s(\sigma
\eta_s)$, with $\lvert \eta_s\rvert\equiv 1$ and $\sigma$ given by
$\sigma_{ss}- \lvert \eta_{ss}\rvert^2 \sigma = -\lvert \eta_{st}\rvert^2$,
with boundary conditions $\sigma(t,1)=\sigma(t,-1)=0$ and $\eta(t,0)=0$. We
prove that the space of arcs is a submanifold of the space of all curves, that
the orthogonal projection exists but is not smooth, and as a consequence we get
a Riemannian exponential map that it continuous and even differentiable but not
$C^1$. This is related to the fact that the curvature is positive but unbounded
above, so that there are conjugate points at arbitrarily short times along any
geodesic.
We also compare this metric to an $L^2$ metric introduced by Michor and
Mumford for shape recognition on the homogeneous space $\text{Imm}(I,
\mathbb{R}^2)/\mathcal{D}(I)$ of immersed curves modulo reparametrizations; we
show it has some similar properties (such as nonnegative but unbounded
curvature and a nonsmooth exponential map), but that the $L^2$ metric on the
arc space yields a genuine Riemannian distance.Comment: 24 page

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