781 research outputs found
The description of gravitational waves in geometric scalar gravity
It is investigated the gravitational waves phenomena in the geometric scalar
theory of gravity (GSG), a class of theories such that gravity is described by
a single scalar field. The associated physical metric describing the spacetime
is constructed from a disformal transformation of Minkowski geometry. In this
theory, a weak field approximation gives rise to a description similar to that
one obtained in general relativity, with the gravitational waves propagating at
the same speed as the light, although they have a characteristic longitudinal
polarization mode, besides others modes that are observer dependent. We also
analyze the energy carried by the gravitational waves as well as how their
emission affects the orbital period of a binary system. Observational data
coming from Hulse and Taylor binary pulsar is then used to constraint the
theory parameter.Comment: Revised version accepted for publication in EPJC; confrontation with
pulsar observational data added; abstract slightly changed. arXiv admin note:
substantial text overlap with arXiv:1607.0103
Viscous Conformal Gauge Theories
We present the conformal behavior of the shear viscosity-to-entropy density
ratio and the fermion-number diffusion coefficient within the perturbative
regime of the conformal window for gauge-fermion theories
Cosmology in GSG
We describe what cosmology looks like in the context of the geometric theory
of gravity (GSG) based on a single scalar field. There are two distinct classes
of cosmological solutions. An interesting feature is the possibility of having
a bounce without invoking exotic equations of state for the cosmic fluid. We
also discuss cosmological perturbation and present the basis of structure
formation by gravitational instability in the framework of the geometric scalar
gravity.Comment: 12 pages, 5 figures, accepted for publication in Phys. Rev.
More about scalar gravity
We discuss a class of models for gravity based on a scalar field. The models
include and generalize the old approach by Nordstr\"om which predated and in
some way inspired General Relativity. The class include also a model that we
have recently introduced and discussed in its cosmological aspects (GSG). We
present here a complete characterisation of the Schwarschild geometry as a
vacuum solution of GSG and sketch a discussion of the first Post-Newtonian
approximation.Comment: 11 pages, 1 figure, accepted for publication in PR
Geometric scalar theory of gravity
We present a geometric scalar theory of gravity. Our proposal will be
described using the "background field method" introduced by Gupta, Feynman and
others as a field theory formulation of general relativity. We analyze previous
criticisms against scalar gravity and show how the present proposal avoids
these difficulties. This concerns not only the theoretical complaints but also
those related to observations. In particular, we show that the widespread
belief of the conjecture that the source of scalar gravity must be the trace of
the energy-momentum tensor - which is one of the main difficulties to couple
gravity with electromagnetic phenomenon in previous models - does not apply to
our geometric scalar theory. Some consequences of the new scalar theory are
explored.Comment: We did some modifications which do not change the content of the tex
XPS analysis of Fe2O3-TiO2-Au nanocomposites prepared by a plasma-assisted route
Fe2O3 nanodeposits have been grown on fluorine-doped tin oxide (FTO) substrates by plasma
enhanced-chemical vapor deposition (PE-CVD). Subsequently, the obtained systems have been
functionalized through the sequential introduction of TiO2 and Au nanoparticles (NPs) by means of
radio frequency (RF)-sputtering. The target nanocomposites have been specifically optimized in
view of their ultimate functional application in solar-driven H2 generation. In the present study, our
attention is focused on a detailed X-ray photoelectron spectroscopy (XPS) characterization of the
surface composition for a representative Fe2O3-TiO2-Au specimen. In particular, this report
provides a detailed discussion of the analyzed C 1s, O 1s, Fe 2p, Ti 2p, and Au 4f regions. The
obtained results point to the formation of pure Fe2O3-TiO2-Au composites, with gold present only
in its metallic state and each of the constituents maintaining its chemical identity
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