174 research outputs found
The analytic structure of heavy quark propagators
The renormalised quark Dyson-Schwinger equation is studied in the limit of
the renormalised current heavy quark mass m_R --> infinity. We are particularly
interested in the analytic pole structure of the heavy quark propagator in the
complex momentum plane. Approximations in which the quark-gluon vertex is
modelled by either the bare vertex or the Ball-Chiu Ansatz, and the Landau
gauge gluon propagator takes either a gaussian form or a gaussian form with an
ultraviolet asymptotic tail are used.Comment: 21 pages Latex and 5 postscript figures. The original version of this
paper has been considerably extended to include a formalism dealing with the
renormalised heavy quark Dyson-Schwinger equation and uses a more realistic
Ansatz for the gluon propagator
Analytic Structure of the Quark Propagator in a Model with an infrared vanishing Gluon Propagator
The Dyson-Schwinger equation for the quark self energy is solved in rainbow
approximation using an infrared (IR) vanishing gluon propagator that introduces
an IR mass scale . There exists a dependent critical coupling indicating
the spontaneous breakdown of chiral symmetry. If one chooses realistic QCD
coupling constants the strength and the scale of spontaneous chiral symmetry
breaking decouple from the IR scale for small while for large no
dynamical chiral symmetry breaking occurs. At timelike momenta the quark
propagator possesses a pole, at least for a large range of the parameter .
Therefore it is suggestive that quarks are not confined in this model for all
values of . Furthermore, we argue that the quark propagator is analytic
within the whole complex momentum plane except on the timelike axis. Hence the
na\"{\i}ve Wick rotation is allowed.Comment: 19 pages, revtex, 7 figures, improved analysis of asymptotic
behaviour and slight changes in conclusion; to appear in Phys.Rev.
Analytic properties of the Landau gauge gluon and quark propagators
We explore the analytic structure of the gluon and quark propagators of
Landau gauge QCD from numerical solutions of the coupled system of renormalized
Dyson--Schwinger equations and from fits to lattice data. We find sizable
negative norm contributions in the transverse gluon propagator indicating the
absence of the transverse gluon from the physical spectrum. A simple analytic
structure for the gluon propagator is proposed. For the quark propagator we
find evidence for a mass-like singularity on the real timelike momentum axis,
with a mass of 350 to 500 MeV. Within the employed Green's functions approach
we identify a crucial term in the quark-gluon vertex that leads to a positive
definite Schwinger function for the quark propagator.Comment: 42 pages, 16 figures, revtex; version to be published in Phys Rev
A discursive approach to narrative accounts of hearing voices and recovery
Substantive objective: To research the range of discursive constructions ârecoveredâ voice hearers employ to describe hearing voices and the implications for positioning and subjectivity (what can be thought and felt) using each construction.
Methodological objective and method: To explore a âsympatheticâ application of Foucauldian discourse analysis, adapting Willigâs (2008 Willig, C. 2008. Introducing Qualitative Research in Psychology, Maidenhead: Open University Press. ) method, analysing two published accounts.
Results and conclusions: Heterogeneous discursive constructions for talking about hearing voices were identified, including: âmany-âselvesââ, âtaking-the-lead-in-your-own-recoveryâ, âvoices-as-an-âimagined-worldââ and âvoices-as-a-coping-strategy-for-dealing-with-traumaâ. The discourse of the biomedical model was not prominent, suggesting alternate discursive constructions may create subjects with a greater capacity for âliving with voicesâ and create a subjectivity from which vantage point the experience holds meaning and value and can be integrated into life experiences. This research may have useful clinical applications for mental health services aiming to collaboratively explore service usersâ ways of understanding hearing voices
MRI identifies plantar plate pathology in the forefoot of patients with rheumatoid arthritis
Previous cadaveric studies have suggested that forefoot deformities at the metatarsophalangeal (MTP) joints in patients with rheumatoid arthritis (RA) might result from the failure of the ligamentous system and displacement of the plantar plates. This study aimed to examine the relationship between plantar plate pathology and the rheumatoid arthritis magnetic resonance imaging score (RAMRIS) of the lesser (second to fifth) MTP joints in patients with RA using high-resolution 3Â T magnetic resonance imaging (MRI). In 24 patients with RA, the forefoot was imaged using 3Â T MRI. Proton density fat-suppressed, T2-weighted fat-suppressed and T1-weighted post gadolinium sequences were acquired through 96 lesser MTP joints. Images were scored for synovitis, bone marrow oedema and bone erosion using the RAMRIS system and the plantar plates were assessed for pathology. Seventeen females and 7 males with a mean age of 55.5Â years (range 37â71) and disease duration of 10.6Â years (range 0.6â36) took part in the study. Plantar plate pathology was most frequently demonstrated on MRI at the fifth MTP joint. An association was demonstrated between plantar plate pathology and RAMRIS-reported synovitis, bone marrow oedema and bone erosion at the fourth and fifth MTP joints. In patients with RA, 3Â T MRI demonstrates that plantar plate pathology at the lesser MTP joints is associated with features of disease severity. Plantar plate pathology is more common at the fourth and fifth MTP joints in subjects with RA in contrast to the predilection for the second MTP reported previously in subjects without RA
Case report: The management of advanced oral cancer in a Jehovah's Witness using the Ultracision Harmonic Scalpel
We present the first case of a head and neck oncological procedure accomplished in a Jehovah's Witness using the Ultracision Harmonic Scalpel (Ethicon, Cincinnati, OH). Jehovah's Witnesses present a serious challenge to the head and neck cancer surgeon due to their refusal to accept transfusion of any blood products. However, our experience reinforces the view that surgical management of head and neck cancer is possible in these patients. We show the Harmonic Scalpel, an ultrasonic tissue dissector, to be a useful surgical tool in obviating the need for blood transfusion. Preoperative optimisation, intra-operative surgical and anaesthetic techniques are also fully discussed
Model gluon propagator and pion and rho-meson observables
A one parameter, model confined-gluon propagator is employed in a
phenomenological application of the Dyson-Schwinger and Bethe-Salpeter
equations to the calculation of a range of - and -meson observables.
Good agreement is obtained with the data. The calculated quark propagator does
not have a singularity on the real- axis. A mass formula for the pion,
involving only the vacuum, dressed quark propagator, is presented and shown to
provide an accurate estimate of the mass obtained via a direct solution of the
Bethe-Salpeter equation.Comment: 17 Pages, no figures, REVTE
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