10,479 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
Future dynamics in f(R) theories
The gravity theories provide an alternative way to explain the current
cosmic acceleration without invoking dark energy matter component. However, the
freedom in the choice of the functional forms of gives rise to the
problem of how to constrain and break the degeneracy among these gravity
theories on theoretical and/or observational grounds. In this paper to proceed
further with the investigation on the potentialities, difficulties and
limitations of gravity, we examine the question as to whether the future
dynamics can be used to break the degeneracy between gravity theories by
investigating the future dynamics of spatially homogeneous and isotropic dust
flat models in two gravity theories, namely the well known gravity and another by A. Aviles et al., whose motivation comes
from the cosmographic approach to gravity. To this end we perform a
detailed numerical study of the future dynamic of these flat model in these
theories taking into account the recent constraints on the cosmological
parameters made by the Planck team. We show that besides being powerful for
discriminating between gravity theories, the future dynamics technique
can also be used to determine the fate of the Universe in the framework of
these gravity theories. Moreover, there emerges from our numerical
analysis that if we do not invoke a dark energy component with
equation-of-state parameter one still has dust flat FLRW solution
with a big rip, if gravity deviates from general relativity via . We also show that FLRW dust solutions with do not
necessarily lead to singularity.Comment: 12 pages, 8 figures. V2: Generality and implications of the results
are emphasized, connection with the recent literature improved, typos
corrected, references adde
The influence of statistical properties of Fourier coefficients on random surfaces
Many examples of natural systems can be described by random Gaussian
surfaces. Much can be learned by analyzing the Fourier expansion of the
surfaces, from which it is possible to determine the corresponding Hurst
exponent and consequently establish the presence of scale invariance. We show
that this symmetry is not affected by the distribution of the modulus of the
Fourier coefficients. Furthermore, we investigate the role of the Fourier
phases of random surfaces. In particular, we show how the surface is affected
by a non-uniform distribution of phases
Local roughness exponent in the nonlinear molecular-beam-epitaxy universality class in one-dimension
We report local roughness exponents, , for three
interface growth models in one dimension which are believed to belong the
non-linear molecular-beam-epitaxy (nMBE) universality class represented by the
Villain-Lais-Das Sarma (VLDS) stochastic equation. We applied an optimum
detrended fluctuation analysis (ODFA) [Luis et al., Phys. Rev. E 95, 042801
(2017)] and compared the outcomes with standard detrending methods. We observe
in all investigated models that ODFA outperforms the standard methods providing
exponents in the narrow interval consistent
with renormalization group predictions for the VLDS equation. In particular,
these exponent values are calculated for the Clarke-Vvdensky and Das
Sarma-Tamborenea models characterized by very strong corrections to the
scaling, for which large deviations of these values had been reported. Our
results strongly support the absence of anomalous scaling in the nMBE
universality class and the existence of corrections in the form
of the one-loop renormalization group analysis
of the VLDS equation
The Signature Triality of Majorana-Weyl Spacetimes
Higher dimensional Majorana-Weyl spacetimes present space-time dualities
which are induced by the Spin(8) triality automorphisms. Different signature
versions of theories such as 10-dimensional SYM's, superstrings, five-branes,
F-theory, are shown to be interconnected via the S_3 permutation group.
Bilinear and trilinear invariants under space-time triality are introduced and
their possible relevance in building models possessing a space-versus-time
exchange symmetry is discussed. Moreover the Cartan's ``vector/chiral
spinor/antichiral spinor" triality of SO(8) and SO(4,4) is analyzed in detail
and explicit formulas are produced in a Majorana-Weyl basis. This paper is the
extended version of hep-th/9907148.Comment: 28 pages, LaTex. Extended version of hep-th/990714
Desenvolvimento de metodologias eletroanalíticas para a determinação de pesticidas em óleo essencial de laranja.
Torsion Gravity: a Reappraisal
The role played by torsion in gravitation is critically reviewed. After a
description of the problems and controversies involving the physics of torsion,
a comprehensive presentation of the teleparallel equivalent of general
relativity is made. According to this theory, curvature and torsion are
alternative ways of describing the gravitational field, and consequently
related to the same degrees of freedom of gravity. However, more general
gravity theories, like for example Einstein-Cartan and gauge theories for the
Poincare and the affine groups, consider curvature and torsion as representing
independent degrees of freedom. By using an active version of the strong
equivalence principle, a possible solution to this conceptual question is
reviewed. This solution favors ultimately the teleparallel point of view, and
consequently the completeness of general relativity. A discussion of the
consequences for gravitation is presented.Comment: RevTeX, 34 pages. Review article to be published by Int. J. Mod.
Phys.
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