1,952 research outputs found
Meson PVV Interactions are determined by Quark Loops
We show that all abnormal parity three-body meson interactions can be
adequately described by quark loops, evaluated at zero external momentum, with
couplings determined by symmetry. We focus primarily on radiative
meson decays which involve one pseudoscalar. The agreement with experiment for
non-rare decays is surprisingly good and requires very few parameters, namely
the coupling constants and and some mixing angles.
This agreement extends to some three-body decays that are dominated by pion
pairs in a P-wave state.Comment: 21 pages, Revtex, one figur
Momentum and Coordinate Space Three-nucleon Potentials
In this paper we give explicit formulae in momentum and coordinate space for
the three-nucleon potentials due to and meson exchange, derived
from off-mass-shell meson-nucleon scattering amplitudes which are constrained
by the symmetries of QCD and by the experimental data. Those potentials have
already been applied to nuclear matter calculations. Here we display additional
terms which appear to be the most important for nuclear structure. The
potentials are decomposed in a way that separates the contributions of
different physical mechanisms involved in the meson-nucleon amplitudes. The
same type of decomposition is presented for the TM force: the
, the chiral symmetry breaking and the nucleon pair terms are isolated.Comment: LATEX, 33 pages, 3 figures (available as postscript files upon
request
Triton calculations with and exchange three-nucleon forces
The Faddeev equations are solved in momentum space for the trinucleon bound
state with the new Tucson-Melbourne and exchange three-nucleon
potentials. The three-nucleon potentials are combined with a variety of
realistic two-nucleon potentials. The dependence of the triton binding energy
on the cut-off parameter in the three-nucleon potentials is studied
and found to be reduced compared to the case with pure exchange. The
exchange parts of the three-nucleon potential yield an overall repulsive
effect. When the recommended parameters are employed, the calculated triton
binding energy turns out to be very close to its experimental value.
Expectation values of various components of the three-nucleon potential are
given to illustrate their significance for binding.Comment: 17 pages Revtex 3.0, 4 figures. Accepted for publication in Phys.
Rev.
Does The 3N-Force Have A Hard Core?
The meson-nucleon dynamics that generates the hard core of the RuhrPot
two-nucleon interaction is shown to vanish in the irreducible 3N force. This
result indicates a small 3N force dominated by conventional light
meson-exchange dynamics and holds for an arbitrary meson-theoretic Lagrangian.
The resulting RuhrPot 3N force is defined in the appendix. A completely
different result is expected when the Tamm-Dancoff/Bloch-Horowitz procedure is
used to define the NN and 3N potentials. In that approach, (e.g. full Bonn
potential) both the NN {\it and} 3N potentials contain non-vanishing
contributions from the coherent sum of meson-recoil dynamics and the
possibility of a large hard core requiring explicit calculation cannot be ruled
out.Comment: 16 pages REVTeX + 3 ps fig
Quadratic momentum dependence in the nucleon-nucleon interaction
We investigate different choices for the quadratic momentum dependence
required in nucleon-nucleon potentials to fit phase shifts in high
partial-waves. In the Argonne v18 potential L**2 and (L.S)**2 operators are
used to represent this dependence. The v18 potential is simple to use in
many-body calculations since it has no quadratic momentum-dependent terms in
S-waves. However, p**2 rather than L**2 dependence occurs naturally in
meson-exchange models of nuclear forces. We construct an alternate version of
the Argonne potential, designated Argonne v18pq, in which the L**2 and (L.S)**2
operators are replaced by p**2 and Qij operators, respectively. The quadratic
momentum-dependent terms are smaller in the v18pq than in the v18 interaction.
Results for the ground state binding energies of 3H, 3He, and 4He, obtained
with the variational Monte Carlo method, are presented for both the models with
and without three-nucleon interactions. We find that the nuclear wave functions
obtained with the v18pq are slightly larger than those with v18 at
interparticle distances < 1 fm. The two models provide essentially the same
binding in the light nuclei, although the v18pq gains less attraction when a
fixed three-nucleon potential is added.Comment: v.2 important corrections in tables and minor revisions in text;
reference for web-posted subroutine adde
Evolution of Nuclear Spectra with Nuclear Forces
We first define a series of NN interaction models ranging from very simple to
fully realistic. We then present Green's function Monte Carlo calculations of
light nuclei to show how nuclear spectra evolve as the nuclear forces are made
increasingly sophisticated. We find that the absence of stable five- and
eight-body nuclei depends crucially on the spin, isospin, and tensor components
of the nuclear force.Comment: 5 pages, 2 figures, submitted to Phys. Rev. Let
Benchmark calculations for polarization observables in 3N scattering
High precision benchmark calculations for phase-shifts and mixing parameters
as well as observables in elastic neutron-deuteron scattering below the
deuteron breakup threshold are presented using a realistic nucleon-nucleon
potential. Two totally different methods, one using a variational principle in
configuration space and the other solving the Faddeev equations in momentum
space are used and compared to each other. The agreement achieved in
phase-shifts and mixing parameters as well as in the polarization observables
is excellent. The extreme sensitivity of the vector analyzing power Ay to small
changes of the phase shifts and mixing parameters is pointed out.Comment: 22 pages, 5 postscript figure
Charge-Asymmetry of the Nucleon-Nucleon Interaction
Based upon the Bonn meson-exchange model for the nucleon-nucleon ()
interaction, we study systematically the charge-symmetry-breaking (CSB) of the
interaction due to nucleon mass splitting. Particular attention is payed
to CSB generated by the -exchange contribution to the interaction,
diagrams, and other multi-meson-exchanges. We calculate the CSB
differences in the effective range parameters as well as phase shift
differences in , and higher partial waves up to 300 MeV lab. energy. We
find a total CSB difference in the singlet scattering length of 1.6 fm which
explains the empirical value accurately. The corresponding CSB phase-shift
differences are appreciable at low energy in the state. In the other
partial waves, the CSB splitting of the phase shifts is small and increases
with energy, with typical values in the order of 0.1 deg at 300 MeV in and
waves.Comment: 11 pages, RevTex, 14 figure
Analyzing power in nucleon-deuteron scattering and three-nucleon forces
Three-nucleon forces have been considered to be one possibility to resolve
the well known discrepancy between experimental values and theoretical
calculations of the nucleon analyzing power in low energy nucleon-deuteron
scattering. In this paper, we investigate possible effects of two-pion exchange
three-nucleon forces on the analyzing power and the differential cross section.
We found that the reason for different effects on the analyzing power by
different three-nucleon forces found in previous calculations is related to the
existence of the contact term. Effects of some variations of two-pion exchange
three-nucleon forces are investigated. Also, an expression for the measure of
the nucleon analyzing power with quartet P-wave phase shifts is presented.Comment: 11 pages including 2 eps figures, use epsfig.sty, to appear in Phys.
Rev.
Experiences of the âNearest Relativeâ provisions in the compulsory detention of people under the Mental Health Act: rapid systematic review
This is the final version. Available from NIHR Journals Library via the DOI in this record.Background
Service users detained for assessment and/or treatment under the Mental Health Act 1983 are allocated a âNearest Relativeâ. The Nearest Relative has access to confidential information about the service user, and can make decisions about their care and treatment. Tensions exist regarding the identification, displacement and powers of the Nearest Relative.
Objectives
To examine the experiences of service users, carers and relevant professionals of the Nearest Relative provisions of the Mental Health Act 1983, and the equivalent Named Person provisions in Scotland. Five research objectives were defined, understanding the experiences of and issues associated with i) identification of the Nearest Relative, ii) displacement of the Nearest Relative, iii) confidentiality and information sharing iv) access to support from carers and v) making decisions about treatment or care.
Data sources
Seven bibliographic databases: MEDLINE (via Ovid), MEDLINE In-Process & Other Non-Indexed Citations (via Ovid), PsycINFO (via Ovid), Social Policy and Practice (via Ovid), HMIC (via Ovid), CINAHL (via EBSCO) and ASSIA (via ProQuest). Citation searching, author contact and grey literature searches were conducted.
Review methods
A rapid systematic review was conducted in six weeks. Evidence published after 1998 was sought from the UK, pertaining to the experiences of those involved in compulsory detention under the Mental Health Act 1983 (or UK variants), including service users, carers, family members, Nearest Relatives, Named Persons, mental health professionals, policy makers and lawyers. Study selection, data extraction and critical appraisal were completed independently by two reviewers. We sought data about experiences obtained through qualitative means or surveys. Included studies containing several paragraphs of participant quotes and/or author interpretations were entered into a framework synthesis; the rest were summarised
descriptively. The framework synthesis was based upon the five research objectives and refined using the findings of key studies from England and Scotland and inductive thematic analysis.
Findings
Twenty studies were included with 12 prioritised for framework synthesis. Four themes emerged i) issues regarding the identification of the Nearest Relative/Named Person, ii) confidentiality and information sharing, iii) enabling use of the Nearest Relative/Named Person role and iv) importance of maintaining relationships. The involvement of service users in choosing their representative and the role of services in supporting the Nearest Relative/Named Person was identified as important.
Limitations
There is little recent evidence to inform this important and complex discussion. The review was rigorously conducted despite the short timescale; however a more in-depth, iterative thematic analysis of all the included studies may have provided additional insights into the mechanisms underpinning the issues.
Conclusions
The Nearest Relative provisions of the Mental Health Act 1983 are complex and of significant importance to individuals detained under the Act and their carers. This rapid review provides specific examples of issues that individuals may experience. More research is needed to aid understanding of this complex topic.
Future work
Primary research specifically focussed on the perceived and actual use and impact of the Nearest Relative provisions in England and Scotland.This report was commissioned by the Department of Health and Social Care via the NIHR HS&DR programme as a review project within NIHR HS&DR programme project number 16/47/22
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