7,512 research outputs found
Teleparallel Spin Connection
A new expression for the spin connection of teleparallel gravity is proposed,
given by minus the contorsion tensor plus a zero connection. The corresponding
minimal coupling is covariant under local Lorentz transformation, and
equivalent to the minimal coupling prescription of general relativity. With
this coupling prescription, therefore, teleparallel gravity turns out to be
fully equivalent to general relativity, even in the presence of spinor fields.Comment: 2 pages, RevTeX, to appear in Phys. Rev D (Brief Report
Primordial magnetic fields constrained by CMB anisotropies and dynamo cosmology
Magneto-curvature stresses could deform magnetic field lines and this would
give rise to back reaction and restoring magnetic stresses [Tsagas, PRL
(2001)]. Barrow et al [PRD (2008)] have shown in Friedman universe the
expansion to be slow down in spatial section of negative Riemann curvatures.
From Chicone et al [CMP (1997)] paper, proved that fast dynamos in compact 2D
manifold implies negatively constant Riemannian curvature, here one applies the
Barrow-Tsagas ideas to cosmic dynamos. Fast dynamo covariant stretching of
Riemann slices of cosmic Lobachevsky plane is given. Inclusion of advection
term on dynamo equations [Clarkson et al, MNRAS (2005)] is considered. In
absence of advection a fast dynamo is also obtained. Viscous and restoring
forces on stretching particles decrease, as magnetic rates increase. From COBE
data (), one computes stretching
.
Zeldovich et al has computed the maximum magnetic growth rate as
. From COBE data one computes
a lower growth rate for the magnetic field as
, well-within Zeldovich et al
estimate. Instead of the Harrison value one obtains the
lower primordial field which yields the
at the Big Bang time.Comment: Dept of theoretical physics-UERJ-Brasi
Gravitation and Duality Symmetry
By generalizing the Hodge dual operator to the case of soldered bundles, and
working in the context of the teleparallel equivalent of general relativity, an
analysis of the duality symmetry in gravitation is performed. Although the
basic conclusion is that, at least in the general case, gravitation is not dual
symmetric, there is a particular theory in which this symmetry shows up. It is
a self dual (or anti-self dual) teleparallel gravity in which, due to the fact
that it does not contribute to the interaction of fermions with gravitation,
the purely tensor part of torsion is assumed to vanish. The ensuing fermionic
gravitational interaction is found to be chiral. Since duality is intimately
related to renormalizability, this theory may eventually be more amenable to
renormalization than teleparallel gravity or general relativity.Comment: 7 pages, no figures. Version 2: minor presentation changes,
references added. Accepted for publication in Int. J. Mod. Phys.
Gravitomagnetic Moments of the Fundamental Fields
The quadratic form of the Dirac equation in a Riemann spacetime yields a
gravitational gyromagnetic ratio \kappa_S = 2 for the interaction of a Dirac
spinor with curvature. A gravitational gyromagnetic ratio \kappa_S = 1 is also
found for the interaction of a vector field with curvature. It is shown that
the Dirac equation in a curved background can be obtained as the square--root
of the corresponding vector field equation only if the gravitational
gyromagnetic ratios are properly taken into account.Comment: 8 pages, RevTeX Style, no figures, changed presentation -- now
restricted to fields of spin 0, 1/2 and 1 -- some references adde
Mass Generation from Lie Algebra Extensions
Applied to the electroweak interactions, the theory of Lie algebra extensions
suggests a mechanism by which the boson masses are generated without resource
to spontaneous symmetry breaking. It starts from a gauge theory without any
additional scalar field. All the couplings predicted by the Weinberg-Salam
theory are present, and a few others which are nevertheless consistent within
the model.Comment: 11 pages; revtex; title and PACS have been changed; comments included
in the manuscrip
Teleparallel origin of the Fierz picture for spin-2 particle
A new approach to the description of spin-2 particle in flat and curved
spacetime is developed on the basis of the teleparallel gravity theory. We show
that such an approach is in fact a true and natural framework for the Fierz
representation proposed recently by Novello and Neves. More specifically, we
demonstrate how the teleparallel theory fixes uniquely the structure of the
Fierz tensor, discover the transparent origin of the gauge symmetry of the spin
2 model, and derive the linearized Einstein operator from the fundamental
identity of the teleparallel gravity. In order to cope with the consistency
problem on the curved spacetime, similarly to the usual Riemannian approach,
one needs to include the non-minimal (torsion dependent) coupling terms.Comment: 5 pages, Revtex4, no figures. Accepted for publication in Phys. Rev.
Efeito do matricondicionamento integrado com controle quimico e biologico na emergencia de plĂąntulas e na produtividade de milho.
Uma das principais causas da baixa produtividade de milho (Zea mays L.) Ă© a qualidade de semente, que afeta o estande inicial e a população de plantas. O objetivo deste trabalho foi avaliar os efeitos da qualidade da semente e da integração do condicionamento matricial (MC) com o tratamento quĂmico (Captan@) e biolĂłgico Kodiak@ (Bacillus subtilis) na emergĂȘncia de plĂąntulas e na produtividade de milho, nas condiçÔes tropicais de Sete Lagoas, MG, e de estresses de frio, em Ponta Grossa, PR. Dois experimentos foram conduzidos na Embrapa Milho e Sorgo, em Sete Lagoas, em 1996 e 1998, e um em Ponta Grossa, PR, em 1997. Sementes de milho hĂbrido foram condicionadas com Micro-Cel E na presença de B. subtilis (600 mg kg-1 de sementes), B. subtilis + Captan@ e ĂĄcido giberĂ©lico (GA4+7 100 uM). Dois lotes de sementes, com germinação de 95% e 85%, foram condicionados Ă razĂŁo de 20: 5: 20, a 22°C, por 48 horas, com MC e na presença de Bacillus. Os parĂąmetros estudados foram: emergĂȘncia de plĂąntulas aos 10 e 20 dias, estande final, Ăndice de velocidade de emergĂȘncia (IVE), nĂșmero de espigas ha-1, produção de grĂŁos e de espigas ha-1. A qualidade inicial do lote de sementes foi fundamental no estabelecimento do estande e na produtividade de milho; a integração do MC com o tratamento quĂmico e biolĂłgico beneficiam a qualidade da semente e a produtividade de milho, especialmente em condiçÔes de estresse. O condicionamento com GA4+7 nĂŁo favoreceu a produtividade de milho e a integração do condicionamento matricial (MC) com o tratamento biolĂłgico (Bacillus) mostrou-se efetiva em aumentar o vigor das sementes de baixa qualidade
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