7,673 research outputs found
Extra polarization states of cosmological gravitational waves in alternative theories of gravity
Cosmological Gravitational Waves (GWs) are usually associated with the
transverse-traceless part of the metric perturbations in the context of the
theory of cosmological perturbations. These modes are just the usual
polarizations `+' and `x' which appear in the general relativity theory.
However, in the majority of the alternative theories of gravity, GWs can
present more than these two polarization states. In this context, the
Newman-Penrose formalism is particularly suitable for evaluating the number of
non-null GW modes. In the present work we intend to take into account these
extra polarization states for cosmological GWs in alternative theories of
gravity. As an application, we derive the dynamical equations for cosmological
GWs for two specific theories, namely, a general scalar-tensor theory which
presents four polarization states and a massive bimetric theory which is in the
most general case with six polarization states for GWs. The mathematical tool
presented here is quite general, so it can be used to study cosmological
perturbations in all metric theories of gravity.Comment: 26 pages, 1 figure. Accepted for publication in Classical and Quantum
Gravity
Hadrons in AdS/QCD models
We discuss applications of gauge/gravity duality to describe the spectrum of
light hadrons. We compare two particular 5-dimensional approaches: a model with
an infrared deformed Anti-de Sitter metric and another one based on a dynamical
AdS/QCD framework with back-reacted geometry in a dilaton/gravity background.
The models break softly the scale invariance in the infrared region and allow
mass gap for the field excitations in the gravity description, while keeping
the conformal property of the metric close to the four-dimensional boundary.
The models provide linear Regge trajectories for light mesons, associated with
specially designed infrared gravity properties. We also review the results for
the decay widths of the f0's into two pions, as overlap integrals between
mesonic string amplitudes, which are in qualitative agreement with data
Desempenho de genótipos de mandioca em um Argissolo eutrófico na região sudoeste da Amazônia.
Objetivou-se com esse trabalho avaliar diferentes genótipos de mandioca quanto ao desempenho agronômico e industrial para a região sudoeste amazônica, em Rondônia
The conservation of energy-momentum and the mass for the graviton
In this work we give special attention to the bimetric theory of gravitation
with massive gravitons proposed by Visser in 1998. In his theory, a prior
background metric is necessary to take in account the massive term. Although in
the great part of the astrophysical studies the Minkowski metric is the best
choice to the background metric, it is not possible to consider this metric in
cosmology. In order to keep the Minkowski metric as background in this case, we
suggest an interpretation of the energy-momentum conservation in Visser's
theory, which is in accordance with the equivalence principle and recovers
naturally the special relativity in the absence of gravitational sources.
Although we do not present a general proof of our hypothesis we show its
validity in the simple case of a plane and dust-dominated universe, in which
the `massive term' appears like an extra contribution for the energy density.Comment: 9 pages, accepted for publishing in GR
E-QED: Electrical Bug Localization During Post-Silicon Validation Enabled by Quick Error Detection and Formal Methods
During post-silicon validation, manufactured integrated circuits are
extensively tested in actual system environments to detect design bugs. Bug
localization involves identification of a bug trace (a sequence of inputs that
activates and detects the bug) and a hardware design block where the bug is
located. Existing bug localization practices during post-silicon validation are
mostly manual and ad hoc, and, hence, extremely expensive and time consuming.
This is particularly true for subtle electrical bugs caused by unexpected
interactions between a design and its electrical state. We present E-QED, a new
approach that automatically localizes electrical bugs during post-silicon
validation. Our results on the OpenSPARC T2, an open-source
500-million-transistor multicore chip design, demonstrate the effectiveness and
practicality of E-QED: starting with a failed post-silicon test, in a few hours
(9 hours on average) we can automatically narrow the location of the bug to
(the fan-in logic cone of) a handful of candidate flip-flops (18 flip-flops on
average for a design with ~ 1 Million flip-flops) and also obtain the
corresponding bug trace. The area impact of E-QED is ~2.5%. In contrast,
deter-mining this same information might take weeks (or even months) of mostly
manual work using traditional approaches
Produção de fitomassa leguminosas isoladas e consorciadas com milheto e teor relativo de clorofila em feijoeiro orgânico em plantio direto.
O objetivo do presente trabalho foi de avaliar a produção de fitomassa de leguminosas isoladas e consorciadas com milheto e seu efeito no teor de clorofila do feijoeiro comum orgânico em sistemas de plantio convencional e direto.CONAFE
On Exact Symmetries and Massless Vectors in Holographic Flows and other Flux Vacua
We analyze the isometries of Type IIB flux vacua based on the
Papadopolous-Tseytlin ansatz and identify the related massless bulk vector
fields. To this end we devise a general ansatz, valid in any flux
compactification, for the fluctuations of the metric and p-forms that
diagonalizes the coupled equations. We then illustrate the procedure in the
simple case of holographic flows driven by the RR 3-form flux only.
Specifically we study the fate of the isometries of the Maldacena-Nunez
solution associated to wrapped D5-branes.Comment: 23 page
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