1,935 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
A Versatile Active Block: DXCCCII and Tunable Applications
The study describes dual-X controlled current conveyor (DXCCCII) as a versatile active block and its application to inductance simulators for testing. Moreover, the high pass filter application using with DXCCCII based inductance simulator and oscillator with flexible tunable oscillation frequency have been presented and simulated to confirm the theoretical validity. The proposed circuit which has a simple circuit design requires the low-voltage and the DXCCCII can also be tuned in the wide range by the biasing current. The proposed DXCCCII provides a good linearity, high output impedance at Z terminals, and a reasonable current and voltage transfer gain accuracy. The proposed DXCCCII and its applications have been simulated using the CMOS 0.18 µm technology
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.
The Demand for Medical Care in Urban China
This is the first paper to investigate the determinants of the demand for medical care in the People's Republic of China. It uses a data set that consists of detailed characteristics of 6407 urban households, a continuous measure of health care spending, and price. A two-part model and a discrete factor model are used in the estimation. Household characteristics and work conditions impact the demand for medical care. Income elasticity is around 0.3, indicating medical care is a necessity. Medical care demand is price inelastic, and price elasticity is larger in absolute value for poorer households.
Newtonian Counterparts of Spin 2 Massless Discontinuities
Massive spin 2 theories in flat or cosmological () backgrounds
are subject to discontinuities as the masses tend to zero. We show and explain
physically why their Newtonian limits do not inherit this behaviour. On the
other hand, conventional ``Newtonian cosmology'', where is a
constant source of the potential, displays discontinuities: e.g. for any finite
range, can be totally removed.Comment: 6 pages, amplifies the ``Newtonian cosmology'' analysis. To appear as
a Class. Quantum Grav. Lette
Spherically symmetric solutions of Einstein + non-polynomial gravities
We obtain the static spherically symmetric solutions of a class of
gravitational models whose additions to the General Relativity (GR) action
forbid Ricci-flat, in particular, Schwarzschild geometries. These theories are
selected to maintain the (first) derivative order of the Einstein equations in
Schwarzschild gauge. Generically, the solutions exhibit both horizons and a
singularity at the origin, except for one model that forbids spherical symmetry
altogether. Extensions to arbitrary dimension with a cosmological constant,
Maxwell source and Gauss-Bonnet terms are also considered.Comment: 6 pages, no figures, REVTeX
Shortcuts to Spherically Symmetric Solutions: A Cautionary Note
Spherically symmetric solutions of generic gravitational models are
optimally, and legitimately, obtained by expressing the action in terms of the
two surviving metric components. This shortcut is not to be overdone, however:
a one-function ansatz invalidates it, as illustrated by the incorrect solutions
of [1].Comment: 2 pages. Amplified derivation, accepted for publication in Class
Quant Gra
Shortcuts to high symmetry solutions in gravitational theories
We apply the Weyl method, as sanctioned by Palais' symmetric criticality
theorems, to obtain those -highly symmetric -geometries amenable to explicit
solution, in generic gravitational models and dimension. The technique consists
of judiciously violating the rules of variational principles by inserting
highly symmetric, and seemingly gauge fixed, metrics into the action, then
varying it directly to arrive at a small number of transparent, indexless,
field equations. Illustrations include spherically and axially symmetric
solutions in a wide range of models beyond D=4 Einstein theory; already at D=4,
novel results emerge such as exclusion of Schwarzschild solutions in cubic
curvature models and restrictions on ``independent'' integration parameters in
quadratic ones. Another application of Weyl's method is an easy derivation of
Birkhoff's theorem in systems with only tensor modes. Other uses are also
suggested.Comment: 10 page
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