3,752 research outputs found
Black hole solution and strong gravitational lensing in Eddington-inspired Born-Infeld gravity
A new theory of gravity called Eddington-inspired Born-Infeld (EiBI) gravity
was recently proposed by Ba\~{n}ados and Ferreira. This theory leads to some
exciting new features, such as free of cosmological singularities. In this
paper, we first obtain a charged EiBI black hole solution with a nonvanishing
cosmological constant when the electromagnetic field is included in. Then based
on it, we study the strong gravitational lensing by the asymptotic flat charged
EiBI black hole. The strong deflection limit coefficients and observables are
shown to closely depend on the additional coupling parameter in the
EiBI gravity. It is found that, compared with the corresponding charged black
hole in general relativity, the positive coupling parameter will
shrink the black hole horizon and photon sphere. Moreover, the coupling
parameter will decrease the angular position and relative magnitudes of the
relativistic images, while increase the angular separation, which may shine new
light on testing such gravity theory in near future by the astronomical
instruments.Comment: 14 pages, 7 figures, 1 table. Two issues on the deflection angle and
photon sphere were corrected and clarifie
Non-coherent Massive SIMO Systems in ISI Channels: Constellation Design and Performance Analysis
A massive single-input multiple-output (SIMO) system with a single transmit
antenna and a large number of receive antennas in intersymbol interference
(ISI) channels is considered. Contrast to existing energy detection (ED)-based
non-coherent receiver where conventional pulse amplitude modulation (PAM) is
employed, we propose a constellation design which minimizes the symbol-error
rate (SER) with the knowledge of channel statistics. To make a comparison, we
derive the SERs of the ED-based receiver with both the proposed constellation
and PAM, namely and . Specifically, asymptotic
behaviors of the SER in regimes of a large number of receive antennas and high
signal-to-noise ratio (SNR) are investigated. Analytical results demonstrate
that the logarithms of both and decrease
approximately linearly with the number of receive antennas, while
degrades faster. It is also shown that the proposed design is of less cost,
because compared with PAM, less antennas are required to achieve the same error
rate
Entropy/Area spectra of the charged black hole from quasinormal modes
With the new physical interpretation of quasinormal modes proposed by
Maggiore, the quantum area spectra of black holes have been investigated
recently. Adopting the modified Hod's treatment, results show that the area
spectra for black holes are equally spaced and the spacings are in a unified
form, , in Einstein gravity. On the other hand,
following Kunstatter's method, the studies show that the area spectrum for a
nonrotating black hole with no charge is equidistant. And for a rotating (or
charged) black hole, it is also equidistant and independent of the angular
momentum (or charge ) when the black hole is far from the extremal case.
In this paper, we mainly deal with the area spectrum of the stringy charged
Garfinkle-Horowitz-Strominger black hole, originating from effective action
that emerges in the low-energy string theory. We find that both methods give
the same results-that the area spectrum is equally spaced and does not depend
on the charge . Our study may provide new insights into understanding the
area spectrum and entropy spectrum for stringy black holes.Comment: 13 pages, no figure
Born-Infeld Black Holes in 4D Einstein-Gauss-Bonnet Gravity
A novel four-dimensional Einstein-Gauss-Bonnet gravity was formulated by D.
Glavan and C. Lin [Phys. Rev. Lett. 124, 081301 (2020)], which is intended to
bypass the Lovelock's theorem and to yield a non-trivial contribution to the
four-dimensional gravitational dynamics. However, the validity and consistency
of this theory has been called into question recently. We study a static and
spherically symmetric black hole charged by a Born-Infeld electric field in the
novel four-dimensional Einstein-Gauss-Bonnet gravity. It is found that the
black hole solution still suffers the singularity problem, since particles
incident from infinity can reach the singularity. It is also demonstrated that
the Born-Infeld charged black hole may be superior to the Maxwell charged black
hole to be a charged extension of the Schwarzschild-AdS-like black hole in this
new gravitational theory. Some basic thermodynamics of the black hole solution
is also analyzed. Besides, we regain the black hole solution in the regularized
four-dimensional Einstein-Gauss-Bonnet gravity proposed by H. L\"u and Y. Pang
[arXiv:2003.11552].Comment: 13 pages and 18 figures, published versio
Learning spatio-temporal representations for action recognition: A genetic programming approach
Extracting discriminative and robust features from video sequences is the first and most critical step in human action recognition. In this paper, instead of using handcrafted features, we automatically learn spatio-temporal motion features for action recognition. This is achieved via an evolutionary method, i.e., genetic programming (GP), which evolves the motion feature descriptor on a population of primitive 3D operators (e.g., 3D-Gabor and wavelet). In this way, the scale and shift invariant features can be effectively extracted from both color and optical flow sequences. We intend to learn data adaptive descriptors for different datasets with multiple layers, which makes fully use of the knowledge to mimic the physical structure of the human visual cortex for action recognition and simultaneously reduce the GP searching space to effectively accelerate the convergence of optimal solutions. In our evolutionary architecture, the average cross-validation classification error, which is calculated by an support-vector-machine classifier on the training set, is adopted as the evaluation criterion for the GP fitness function. After the entire evolution procedure finishes, the best-so-far solution selected by GP is regarded as the (near-)optimal action descriptor obtained. The GP-evolving feature extraction method is evaluated on four popular action datasets, namely KTH, HMDB51, UCF YouTube, and Hollywood2. Experimental results show that our method significantly outperforms other types of features, either hand-designed or machine-learned
A local structural descriptor for image matching via normalized graph laplacian embedding
This paper investigates graph spectral approaches to the problem of point pattern matching. Specifically, we concentrate on the issue of how to effectively use graph spectral properties to characterize point patterns in the presence of positional jitter and outliers. A novel local spectral descriptor is proposed to represent the attribute domain of feature points. For a point in a given point-set, weight graphs are constructed on its neighboring points and then their normalized Laplacian matrices are computed. According to the known spectral radius of the normalized Laplacian matrix, the distribution of the eigenvalues of these normalized Laplacian matrices is summarized as a histogram to form a descriptor. The proposed spectral descriptor is finally combined with the approximate distance order for recovering correspondences between point-sets. Extensive experiments demonstrate the effectiveness of the proposed approach and its superiority to the existing methods
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