10,048 research outputs found
Second Repeating FRB 180814.J0422+73: Ten-year Fermi-LAT Upper Limits and Implications
The second repeating fast radio burst source, FRB 180814.J0422+73, was detected recently by the CHIME collaboration. We use the ten-year Fermi Large Area Telescope archival data to place a flux upper limit in the energy range of 100 MeV−10 GeV at the position of the source, which is ~1.1 × 10−11 erg cm−2 s−1 for a six-month time bin on average, and ~2.4 × 10−12 erg cm−2 s−1 for the entire ten-year time span. For the maximum redshift of z = 0.11, the ten-year upper limit of luminosity is ~7.3 × 1043 erg s−1. We utilize these upper limits to constrain the fast radio burst (FRB) progenitor and central engine. For the rotation-powered young magnetar model, the upper limits can pose constraints on the allowed parameter space for the initial rotational period and surface magnetic field of the magnetar. We also place significant constraints on the kinetic energy of a relativistic external shock wave, ruling out the possibility that there existed a gamma-ray burst (GRB) beaming toward Earth during the past ten years as the progenitor of the repeater. The case of an off-beam GRB is also constrained if the viewing angle is not much greater than the jet opening angle. All of these constraints are more stringent if FRB 180814.J0422+73 is at a closer distance
Brane worlds in gravity with auxiliary fields
Recently, Pani, Sotiriou, and Vernieri explored a new theory of gravity by
adding nondynamical fields, i.e., gravity with auxiliary fields [Phys. Rev. D
88, 121502(R) (2013)]. In this gravity theory, higher-order derivatives of
matter fields generically appear in the field equations. In this paper we
extend this theory to any dimensions and discuss the thick braneworld model in
five dimensions. Domain wall solutions are obtained numerically. The stability
of the brane system under the tensor perturbation is analyzed. We find that the
system is stable under the tensor perturbation and the gravity zero mode is
localized on the brane. Therefore, the four-dimensional Newtonian potential can
be realized on the brane.Comment: 7 pages, 4 figure
Resummation of Boson-Jet Correlation at Hadron Colliders
We perform a precise calculation of the transverse momentum ()
distribution of the boson+jet system in boson production events. The boson can
be either a photon, , or Higgs boson with mass , and is
the sum of the transverse momenta of the boson and the leading jet with
magnitude . Using renormalization group techniques and
soft-collinear effective theory, we resum logarithms and
at next-to-leading logarithmic accuracy including the non-global logarithms,
where and are respectively the hard scattering energy and the radius of
the jet. Specifically, we investigate two scenarios of or
in +jet events, and we examine the distributions
with different jet radii and study the effect of non-global logarithms. In the
end we compare our theoretical calculations with Monte Carlo simulations and
data from the LHC.Comment: 35 pages, 7 figure
Image Restoration Using Very Deep Convolutional Encoder-Decoder Networks with Symmetric Skip Connections
In this paper, we propose a very deep fully convolutional encoding-decoding
framework for image restoration such as denoising and super-resolution. The
network is composed of multiple layers of convolution and de-convolution
operators, learning end-to-end mappings from corrupted images to the original
ones. The convolutional layers act as the feature extractor, which capture the
abstraction of image contents while eliminating noises/corruptions.
De-convolutional layers are then used to recover the image details. We propose
to symmetrically link convolutional and de-convolutional layers with skip-layer
connections, with which the training converges much faster and attains a
higher-quality local optimum. First, The skip connections allow the signal to
be back-propagated to bottom layers directly, and thus tackles the problem of
gradient vanishing, making training deep networks easier and achieving
restoration performance gains consequently. Second, these skip connections pass
image details from convolutional layers to de-convolutional layers, which is
beneficial in recovering the original image. Significantly, with the large
capacity, we can handle different levels of noises using a single model.
Experimental results show that our network achieves better performance than all
previously reported state-of-the-art methods.Comment: Accepted to Proc. Advances in Neural Information Processing Systems
(NIPS'16). Content of the final version may be slightly different. Extended
version is available at http://arxiv.org/abs/1606.0892
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