2,315 research outputs found
Interacting spin 0 fields with torsion via Duffin-Kemmer-Petiau theory
Here we study the behaviour of spin 0 sector of the DKP field in spaces with
torsion. First we show that in a Riemann-Cartan manifold the DKP field presents
an interaction with torsion when minimal coupling is performed, contrary to the
behaviour of the KG field, a result that breaks the usual equivalence between
the DKP and the KG fields.
Next we analyse the case of Teleparallel Equivalent of General Relativity
Weitzenbock manifold, showing that in this case there is a perfect agreement
between KG and DKP fields. The origins of both results are also discussed.Comment: 10 pages, no figures, uses REVTEX. Changes in the presentation, minor
misprints and one equation corrected. References updated. To appear in
General Relativity and Gravitatio
Conformal invariance of massless Duffin-Kemmer-Petiau theory in Riemannian space-times
We investigate the conformal invariance of massless Duffin-Kemmer-Petiau
theory coupled to riemannian space-times. We show that, as usual, in the
minimal coupling procedure only the spin 1 sector of the theory -which
corresponds to the electromagnetic field- is conformally invariant. We show
also that the conformal invariance of the spin 0 sector can be naturally
achieved by introducing a compensating term in the lagrangian. Such a procedure
-besides not modifying the spin 1 sector- leads to the well-known conformal
coupling between the scalar curvature and the massless Klein-Gordon-Fock field.
Going beyond the riemannian spacetimes, we briefly discuss the effects of a
nonvanishing torsion in the scalar case.Comment: 8 pages, no figures. Major changes in contend and results. To appear
in Class.Quant.Gra
Spin 1 fields in Riemann-Cartan space-times "via" Duffin-Kemmer-Petiau theory
We consider massive spin 1 fields, in Riemann-Cartan space-times, described
by Duffin-Kemmer-Petiau theory. We show that this approach induces a coupling
between the spin 1 field and the space-time torsion which breaks the usual
equivalence with the Proca theory, but that such equivalence is preserved in
the context of the Teleparallel Equivalent of General Relativity.Comment: 8 pages, no figures, revtex. Dedicated to Professor Gerhard Wilhelm
Bund on the occasion of his 70th birthday. To appear in Gen. Rel. Grav.
Equations numbering corrected. References update
Relativistic Tunneling Through Two Successive Barriers
We study the relativistic quantum mechanical problem of a Dirac particle
tunneling through two successive electrostatic barriers. Our aim is to study
the emergence of the so-called \emph{Generalized Hartman Effect}, an effect
observed in the context of nonrelativistic tunneling as well as in its
electromagnetic counterparts, and which is often associated with the
possibility of superluminal velocities in the tunneling process. We discuss the
behavior of both the phase (or group) tunneling time and the dwell time, and
show that in the limit of opaque barriers the relativistic theory also allows
the emergence of the Generalized Hartman Effect. We compare our results with
the nonrelativistic ones and discuss their interpretation.Comment: 7 pages, 3 figures. Revised version, with a new appendix added.
Slightly changes in the styles and captions of Figures 1 and 2. To appear in
Physical Review
Paraganglioma of the cauda equina region
BACKGROUND CONTEXT: Cauda equina paragangliomas (CEPs) are rare neuroendocrine tumors.
The difficulty in differential diagnosis with other tumors of this region may be misleading for
surgical planning and prognostic expectations.
PURPOSE: To report on a rare case of CEP and review the most current information regarding the
diagnosis, treatment options, and outcomes.
STUDY DESIGN: Case report and literature review.
PATIENT SAMPLE: One patient affected by CEP.
METHODS: We report on a 33-year-old woman with a 2-month history of worsening low back
pain, aggravated by sitting, bending, and coughing. Neurological examination revealed normal
power and muscular tone, no sensory or sphincter abnormality, and normal reflex. Magnetic resonance
imaging of the lumbar spine demonstrated an intradural extramedullary lesion at L3, with
homogeneous contrast enhancement and hypointense punctate foci. The patient underwent an L3
laminectomy and tumor removal. Relevant articles covering CEPs from 1970 to the present were
reviewed.
RESULTS: The histopathological examinations described paraganglioma features. The postoperative
coursewas uneventful, and all the symptoms resolved, with no tumor recurrence after 3 years’ follow-up.
CONCLUSIONS: Cauda equina paragangliomas are rare, benign, and slow-growing tumors. Except
for its secreting tumor characteristics, preoperative CEP diagnosis is very difficult.Magnetic resonance
imaging is important andmay suggest specific radiological features for these tumors; however, these are
only relative, and it is rare that diagnosis ismade before surgery.Diagnosis is established by histological
examination and electron microscopy, and immunohistochemical techniques must be used to achieve a
correct diagnosis. Cauda equina paragangliomas arewell-encapsulated tumors that may be cured by surgery
alone, whereas radiotherapy is reserved for incompletely resected tumors. Overall, prolonged postoperative
observation is mandatory because of the slow tumor evolution and the possibility of tumor
relapse even up to 30 years after surgery
Bose-Einstein Condensation and Free DKP field
The thermodynamical partition function of the Duffin-Kemmer-Petiau theory is
evaluated using the imaginary-time formalism of quantum field theory at finite
temperature and path integral methods. The DKP partition function displays two
features: (i) full equivalence with the partition function for charged scalar
particles and charged massive spin 1 particles; and (ii) the zero mode sector
which is essential to reproduce the well-known relativistic Bose-Einstein
condensation for both theories.Comment: 12 pages, 2 eps figures. To be published in Physics Letter
Electromagnetic field at Finite Temperature: A first order approach
In this work we study the electromagnetic field at Finite Temperature via the
massless DKP formalism. The constraint analysis is performed and the partition
function for the theory is constructed and computed. When it is specialized to
the spin 1 sector we obtain the well-known result for the thermodynamic
equilibrium of the electromagnetic field.Comment: 6 pages, Latex2e, title changed and minimal modification
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