203 research outputs found
Analysis of the instantaneous Bethe-Salpeter equation for -bound-states
We investigate the structure of the instantaneous Bethe-Salpeter equation for
-bound states in the general case of unequal quark masses and
develop a numerical scheme for the calculation of mass spectra and
Bethe-Salpeter amplitudes. In order to appreciate the merits of the various
competing models beyond the reproduction of the mass spectra we present
explicit formulas to calculate electroweak decays. The results for an explicit
quark model will be compared to experimental data in a subsequent paperComment: 11 pages, RevTeX, TK-93-1
Vector and Axial Form Factors Applied to Neutrino Quasielastic Scattering
We calculate the quasielastic cross sections for neutrino scattering on
nucleons using up to date fits to the nucleon elastic electromagnetic form
factors GEp, GEn, GMp, GMn, and weak form factors. We show the extraction of Fa
for neutrino experiments. We show how well \minerva, a new approved experiment
at FNAL, can measure Fa. We show the that Fa has a different contribution to
the anti-neutrino cross section, and how the anti-neutrino data can be used to
check Fa extracted from neutrino scattering.Comment: Presented by Howard Budd at NuInt04, Mar. 2004, Laboratori Nazionali
del Gran Sasso - INFN - Assergi, Ital
(In-)Consistencies in the relativistic description of excited states in the Bethe-Salpeter equation
The Bethe-Salpeter equation provides the most widely used technique to
extract bound states and resonances in a relativistic Quantum Field Theory.
Nevertheless a thorough discussion how to identify its solutions with physical
states is still missing. The occurrence of complex eigenvalues of the
homogeneous Bethe-Salpeter equation complicates this issue further. Using a
perturbative expansion in the mass difference of the constituents we
demonstrate for scalar fields bound by a scalar exchange that the underlying
mechanism which results in complex eigenvalues is the crossing of a normal (or
abnormal) with an abnormal state. Based on an investigation of the
renormalization of one-particle properties we argue that these crossings happen
beyond the applicability region of the ladder Bethe-Salpeter equation. The
implications for a fermion-antifermion bound state in QED are discussed, and a
consistent interpretation of the bound state spectrum of QED is proposed.Comment: 39 pages, 14 figures, LaTeX2e, uses amssymb, minor changes,
references added, to appear in Annals Phy
Inconsistencies of Massive Charged Gravitating Higher Spins
We examine the causality and degrees of freedom (DoF) problems encountered by
charged, gravitating, massive higher spin fields. For spin s=3/2, making the
metric dynamical yields improved causality bounds. These involve only the mass,
the product eM_P of the charge and Planck mass and the cosmological constant
\Lambda. The bounds are themselves related to a gauge invariance of the
timelike component of the field equation at the onset of acausality. While
propagation is causal in arbitrary E/M backgrounds, the allowed mass ranges of
parameters are of Planck order. Generically, interacting spins s>3/2 are
subject to DoF violations as well as to acausality; the former must be overcome
before analysis of the latter can even begin. Here we review both difficulties
for charged s=2 and show that while a g-factor of 1/2 solves the DoF problem,
acausality persists for any g. Separately we establish that no s=2 theory --DoF
preserving or otherwise -- can be tree unitary.Comment: 25 pages, late
On the instantaneous Bethe-Salpeter equation
We present a systematic algebraic and numerical investigation of the
instantaneous Bethe-Salpeter equation. Emphasis is placed on confining
interaction kernels of the Lorentz scalar, time component vector, and full
vector types. We explore stability of the solutions and Regge behavior for each
of these interactions, and conclude that only time component vector confinement
leads to normal Regge structure and stable solutions.Comment: Latex (uses epsf macro), 26 pages of text, 12 postscript figures
included
Massive Spin 3/2 Electrodynamics
We study the general non-minimally coupled charged massive spin 3/2 model
both for its low energy phenomenological properties and for its unitarity,
causality and degrees of freedom behaviour. When the model is viewed as an
effective theory, its parameters (after ensuring the correct excitation count)
are related to physical characteristics, such as the magnetic moment g factor,
by means of low energy theorems. We also provide the corresponding higher spin
generalisation. Separately, we consider both low and high energy unitarity, as
well as the causality aspects of our models. None (including truncated N=2
supergravity) is free of the minimal model's acausality.Comment: 23 pages, 1 figure, LaTeX and axodraw.sty, novel Majorana-type term
included; results unaltere
Whole home exercise intervention for depression in older care home residents (the OPERA study) : a process evaluation
Background:
The ‘Older People’s Exercise intervention in Residential and nursing Accommodation’ (OPERA) cluster randomised trial evaluated the impact of training for care home staff together with twice-weekly, physiotherapist-led exercise classes on depressive symptoms in care home residents, but found no effect. We report a process evaluation exploring potential explanations for the lack of effect.
Methods:
The OPERA trial included over 1,000 residents in 78 care homes in the UK. We used a mixed methods approach including quantitative data collected from all homes. In eight case study homes, we carried out repeated periods of observation and interviews with residents, care staff and managers. At the end of the intervention, we held focus groups with OPERA research staff. We reported our first findings before the trial outcome was known.
Results:
Homes showed large variations in activity at baseline and throughout the trial. Overall attendance rate at the group exercise sessions was low (50%). We considered two issues that might explain the negative outcome: whether the intervention changed the culture of the homes, and whether the residents engaged with the intervention. We found low levels of staff training, few home champions for the intervention and a culture that prioritised protecting residents from harm over encouraging activity. The trial team delivered 3,191 exercise groups but only 36% of participants attended at least 1 group per week and depressed residents attended significantly fewer groups than those who were not depressed. Residents were very frail and therefore most groups only included seated exercises.
Conclusions:
The intervention did not change the culture of the homes and, in the case study homes, activity levels did not change outside the exercise groups. Residents did not engage in the exercise groups at a sufficient level, and this was particularly true for those with depressive symptoms at baseline. The physical and mental frailty of care home residents may make it impossible to deliver a sufficiently intense exercise intervention to impact on depressive symptoms
The angular distribution of the reaction
The reaction is very important for low-energy
( MeV) antineutrino experiments. In this paper we calculate
the positron angular distribution, which at low energies is slightly backward.
We show that weak magnetism and recoil corrections have a large effect on the
angular distribution, making it isotropic at about 15 MeV and slightly forward
at higher energies. We also show that the behavior of the cross section and the
angular distribution can be well-understood analytically for MeV by calculating to , where is the nucleon mass. The
correct angular distribution is useful for separating events from other reactions and detector backgrounds, as well as for
possible localization of the source (e.g., a supernova) direction. We comment
on how similar corrections appear for the lepton angular distributions in the
deuteron breakup reactions and . Finally, in the reaction , the
angular distribution of the outgoing neutrons is strongly forward-peaked,
leading to a measurable separation in positron and neutron detection points,
also potentially useful for rejecting backgrounds or locating the source
direction.Comment: 10 pages, including 5 figure
On the broken gauge, conformal and discrete symmetries in particle physics
Relationships between gauge, conformal and discrete symmetries in particle
physics are analysed. We study also the effect of the electroweak mixing on the
cancellation of SU(2) anomalous actions. It is shown that the relation
theta_{W} = 2(theta_{12}+theta_{23}+theta_{13}) between the Weinberg angle and
the Cabibbo-Kobayashi-Maskawa angles should be satisfied and this effect is
completely defined by the mixing of Dirac fermions. We compare two mechanisms
of the spontaneous breaking of gauge symmetry, discuss the renormalizability of
theories, and argue for the existence of the Majorana fermions necessary to
remove the SU(2) anomalous action. The fate of the majoron and the
spontaneously broken lepton number is discussed. We also show the compatibility
of the boson and fermion mixings with Dyson-Schwinger equations.Comment: 27 pages, LaTeX style; v2: published version, two figures adde
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