2,693 research outputs found
Conformal Properties of Charges in Scalar-Tensor Gravities
We study the behavior under conformal transformations of energy and other
charges in generic scalar-tensor models. This enables us to conclude that the
ADM/AD masses are invariant under field redefinitions mixing metric and scalar
despite the permitted slow asymptotic falloff of massless scalars.Comment: 4 page
New Energy Definition for Higher Curvature Gravities
We propose a novel but natural definition of conserved quantities for gravity
models quadratic and higher in curvature. Based on the spatial asymptotics of
curvature rather than of metric, it avoids the GR energy machinery's more
egregious problems--such as zero energy "theorems" and failure in flat
backgrounds -- in this fourth-derivative realm. In D>4, the present expression
indeed correctly discriminates between second derivative Gauss-Bonnet and
generic, fourth derivative, actions.Comment: 3 pages, Typos fixe
Massive, Topologically Massive, Models
In three dimensions, there are two distinct mass-generating mechanisms for
gauge fields: adding the usual Proca/Pauli-Fierz, or the more esoteric
Chern-Simons (CS), terms. Here we analyze the three-term models where both
types are present, and their various limits. Surprisingly, in the tensor case,
these seemingly innocuous systems are physically unacceptable. If the sign of
the Einstein term is ``wrong'' as is in fact required in the CS case, then the
excitation masses are always complex; with the usual sign, there is a (known)
region of the two mass parameters where reality is restored, but instead we
show that a ghost problem arises, while, for the ``pure mass'' two-term system
without an Einstein action, complex masses are unavoidable. This contrasts with
the smooth behavior of the corresponding vector models. Separately, we show
that the ``partial masslessness'' exhibited by (plain) massive spin-2 models in
de Sitter backgrounds is formally shared by the three-term system: it also
enjoys a reduced local gauge invariance when this mass parameter is tuned to
the cosmological constant.Comment: 7 pages, typos corrected, reference adde
Systematics on ground-state energies of nuclei within the neural networks
One of the fundamental ground-state properties of nuclei is binding energy.
In this study, we have employed artificial neural networks (ANNs) to obtain
binding energies based on the data calculated from Hartree-Fock-Bogolibov (HFB)
method with the two SLy4 and SKP Skyrme forces. Also, ANNs have been employed
to obtain two-neutron and two-proton separation energies of nuclei. Statistical
modeling of nuclear data using ANNs has been seen as to be successful in this
study. Such a statistical model can be possible tool for searching in
systematics of nuclei beyond existing experimental nuclear data.Comment: 7 pages, 6 figure
An artificial neural network application on nuclear charge radii
The artificial neural networks (ANNs) have emerged with successful
applications in nuclear physics as well as in many fields of science in recent
years. In this paper, by using (ANNs), we have constructed a formula for the
nuclear charge radii. Statistical modeling of nuclear charge radii by using
ANNs has been seen as to be successful. Also, the charge radii, binding
energies and two-neutron separation energies of Sn isotopes have been
calculated by implementing of the new formula in Hartree-Fock-Bogoliubov (HFB)
calculations. The results of the study shows that the new formula is useful for
describing nuclear charge radii.Comment: 7 pages, 3 figure
Weyl-gauging of Topologically Massive Gravity
We construct a Weyl-invariant extension of topologically massive gravity
which, remarkably, turns out to include topologically massive electrodynamics,
with a Proca mass term, conformally coupled to a scalar field. The action has
no dimensionful parameters, therefore, the masses are generated via symmetry
breaking either radiatively in flat backgrounds or spontaneously in constant
curvature backgrounds. The broken phase of the theory, generically, has a
single massive spin-2 and a massive spin-1 excitation. Chiral gravity in
asymptotically anti-de Sitter spacetimes does not arise as a low energy theory,
while chiral gravity in de Sitter spacetime is not ruled out.Comment: 10 pages, minor changes made, version to appear in Phys. Rev.
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