17,499 research outputs found
A Rotating Charged Black Hole Solution in f(R) Gravity
In the context of f(R) theories of gravity, we address the problem of finding
a rotating charged black hole solution in the case of constant curvature. The
new metric is obtained by solving the field equations and we show that the
behavior of it is typical of a rotating charged source. In addition, we analyze
the thermodynamics of the new black hole. The results ensures that the
thermodynamical properties in f(R) gravities are qualitatively similar to those
of standard General Relativity.Comment: 9 pages, no figure
A f(R) gravity without cosmological constant
In this work we consider the possibility of describing the current evolution
of the universe, without the introduction of any cosmological constant or dark
energy (DE), by modifying the Einstein-Hilbert (EH) action. In the context of
the f(R) gravities within the metric formalism, we show that it is possible to
find an action without cosmological constant which exactly reproduces the
behavior of the EH action with cosmological constant. In addition the f(R)
action is analytical at the origin having Minkowski and Schwarzschild as vacuum
solutions. The found f(R) action is highly non-trivial and must be written in
terms of hypergeometric functions but, in spite of looking somewhat artificial,
it shows that the cosmological constant, or more generally the DE, is not a
logical necessity.Comment: 5 pages, no figure
Towards a new quantization of Dirac's monopole
There are several mathematical and physical reasons why Dirac's quantization
must hold. How far one can go without it remains an open problem. The present
work outlines a few steps in this direction.Comment: To appear in Proceedings of "IV Taller de la Division de Gravitacion
y Fisica Matematica". Misprints corrected, references and acknowledgments
adde
Sparse inversion of Stokes profiles. I. Two-dimensional Milne-Eddington inversions
Inversion codes are numerical tools used for the inference of physical
properties from the observations. Despite their success, the quality of current
spectropolarimetric observations and those expected in the near future presents
a challenge to current inversion codes. The pixel-by-pixel strategy of
inverting spectropolarimetric data that we currently utilize needs to be
surpassed and improved. The inverted physical parameters have to take into
account the spatial correlation that is present in the data and that contains
valuable physical information. We utilize the concept of sparsity or
compressibility to develop an new generation of inversion codes for the Stokes
parameters. The inversion code uses numerical optimization techniques based on
the idea of proximal algorithms to impose sparsity. In so doing, we allow for
the first time to exploit the presence of spatial correlation on the maps of
physical parameters. Sparsity also regularizes the solution by reducing the
number of unknowns. We compare the results of the new inversion code with
pixel-by-pixel inversions, demonstrating the increase in robustness of the
solution. We also show how the method can easily compensate for the effect of
the telescope point spread function, producing solutions with an enhanced
contrast.Comment: 13 pages, 8 figures, accepted for publication in A&
Real-time multiframe blind deconvolution of solar images
The quality of images of the Sun obtained from the ground are severely
limited by the perturbing effect of the turbulent Earth's atmosphere. The
post-facto correction of the images to compensate for the presence of the
atmosphere require the combination of high-order adaptive optics techniques,
fast measurements to freeze the turbulent atmosphere and very time consuming
blind deconvolution algorithms. Under mild seeing conditions, blind
deconvolution algorithms can produce images of astonishing quality. They can be
very competitive with those obtained from space, with the huge advantage of the
flexibility of the instrumentation thanks to the direct access to the
telescope. In this contribution we leverage deep learning techniques to
significantly accelerate the blind deconvolution process and produce corrected
images at a peak rate of ~100 images per second. We present two different
architectures that produce excellent image corrections with noise suppression
while maintaining the photometric properties of the images. As a consequence,
polarimetric signals can be obtained with standard polarimetric modulation
without any significant artifact. With the expected improvements in computer
hardware and algorithms, we anticipate that on-site real-time correction of
solar images will be possible in the near future.Comment: 16 pages, 12 figures, accepted for publication in A&
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