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