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An oscillating, homogeneous and isotropic Universe from Scalar-Tensor gravity
Abstract
An oscillating, homogeneous and isotropic Universe which arises from Scalar-Tensor gravity is discussed in the linearized approach, showing that some observative evidences like the Hubble Law and the Cosmological Redshift are in agreement with the model. In this context Dark Energy appears like a pure curvature effect arising by the scalar field. Comment: Integration of of a previous research on oscillating Universes published in Gen. Rel. Grav. DOI: 10.1007/s/10714-088-0627-3. The paper has been accepted for publication by the International Journal of Theoretical Physics, Group Theory and Nonlinear Optics
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Based on the dynamical equivalence between higher order gravity and scalar-tensor gravity the parametrized post-Newtonian (PPN) limit of fourth order gravity is discussed. We exploit this analogy developing a fourth order gravity version of the Eddington PPN parameters. As a result, Solar System experiments can be reconciled with higher order gravity, if physical constraints descending from experiments are fulfilled.
In this paper we show that information on both the differential and common mode free-mass response to a gravitational wave can provide important information on discriminating the direction of the gravitational wave source and between different theories of gravitation. The conventional Michelson interferometer scheme only measures the differential free-mass response. By changing the orientation of the beam splitter, it is possible to configure the detector so it is sensitive to the common-mode of the free-mass motion. The proposed interferometer is an adaptation of the Fox-Smith interferometer. A major limitation to the new scheme is its enhanced sensitivity to laser frequency fluctuations over the conventional, and we propose a method of cancelling these fluctuations. The configuration could be used in parallel to the conventional differential detection scheme with a significant sensitivity and bandwidth.
The Einstein equations with quantum one-loop contributions of conformally covariant matter fields are shown to admit a class of nonsingular isotropic homogeneous solutions that correspond to a picture of the Universe being initially in the most symmetric (de Sitter) state.
Newtonian limit of Extended Theories of Gravity (in particular, higher--order and scalar--tensor theories) is theoretically discussed taking into account recent observational and experimental results.
Scalar-tensor gravity admits the existence of scalar modes of gravitational waves (SGWs). The mechanism of production and the response of interferometers to these scalar components of gravitational waves can be studied in three different gauges in the massless case: the transverse-traceless (TT) gauge, the so-called "Shibata, Nakao and Nakamura" (SNN) gauge, and the local Lorentz gauge. The response of interferometers to massless SGWs is invariant in these different gauges. Our work generalizes previous results which, in the study of the coupling between interferometers and massless SGWs, started from the assumption that the wavelength of the SGW is much larger than the distance between the test masses. Furthermore, considering situations motivated by string-dilaton gravity, the effect of a small mass term on the response of the interferometer is taken into account. In this case (massive SGW), we have a longitudinal effect, the response of an arm of an interferometer, which is aligned in the wave propagation direction is computed. The value of the longitudinal response function for non-relativistic massive SGW at high frequencies is very high: this fact opens the doors to the interesting possibility of detection of "massive" part of the signal, if advanced projects will achieve high sensitivities. Finally, by using previous results and the geometry of the system, the generalized coupling between interferometers (like VIRGO or LIGO) and massless SGWs is studied. The total frequency response function to massless SGWs incoming from arbitrary directions is studied.
During the last twenty years, dramatic improvements in methods of observing astrophysical phenomena from the ground and in space have added to our knowledge of what the universe is like now and what it was like in the past, going back to the hot big bang. In this overview of today's physical cosmology, P.J.E. Peebles shows how observation has combined with theoretical elements to establish the subject as a mature science, while he also discusses the most notable recent attempts to understand the origin and structure of the universe. A successor to Peebles's classic volume Physical Cosmology (Princeton, 1971), the book is a comprehensive overview addressed not only to students but also to scientists active in fields outside cosmology. The first chapter of the work presents the elements of physical cosmology, including the history of the discovery of the expanding universe. The second, on the cosmological tests that measure the geometry of spacetime, discusses general relativity theory as the basis for the tests, and then surveys the broad variety of ways the tests can be applied with the new generations of telescopes and detectors. The third chapter deals with the origin of galaxies and the large-scale structure of the universe, and reviews ideas about how the evolution of the universe might be traced back to very early epochs when structure originated. Each section of these chapters begins with an introduction that can be understood with no special knowledge beyond undergraduate physics, and then progresses to more specialized topics. P.J.E. Peebles is Albert Einstein Professor of Science at Princeton University. He is a Fellow of the American Academy of Arts and Sciences and the Royal Society.
It is argued that the evolution of the universe proceeded from a nearly
uniform initial state to a progressively more irregular and clumpy
universe. The discussion centers on the clusters of galaxies, the
empirical evidence of the nature of clustering, and theories of how the
clustering evolves in an expanding universe. A historical introduction
to the subject is given; and a survey of methods used to deal with the
Newtonian approximation to the theory of the evolution of the mass
distribution is presented. Recent progress in the use of statistical
measures of the clustering is described; and techniques for dealing with
cosmic evolution, in the statistical measures of clustering and under
general relativity theory, are considered. An assessment is made of
attempts to link theory and observation to arrive at a well-established
physical picture of the nature and evolution of the universe.
The GEO 600 gravitational wave detector located near Hannover in Germany is part of an international network of gravitational wave observatories. As more and more of these detectors approach their final configuration, the focus is shifted from commissioning to detector characterization. At the moment, GEO 600, the first detector using advanced technologies such as dual recycling, is preparing for a long data-taking period starting at the beginning of summer 2006. In this paper, we give an overview of detector commissioning and the detector characterization work of GEO 600 for the period between March 2005 and February 2006.
We review various modified gravities considered as gravitational alternative for dark energy. Specifically, we consider the versions of f(R), f(G) or f(R,G) gravity, model with non-linear gravitational coupling or string-inspired model with Gauss-Bonnet-dilaton coupling in the late universe where they lead to cosmic speed-up. It is shown that some of such theories may pass the Solar System tests. On the same time, it is demonstrated that they have quite rich cosmological structure: they may naturally describe the effective (cosmological constant, quintessence or phantom) late-time era with a possible transition from decceleration to acceleration thanks to gravitational terms which increase with scalar curvature decrease. The possibility to explain the coincidence problem as the manifestation of the universe expansion in such models is mentioned. The late (phantom or quintessence) universe filled with dark fluid with inhomogeneous equation of state (where inhomogeneous terms are originated from the modified gravity) is also described. Comment: LaTeX file, 21 pages, references are added, lectures for 42 Karpacz Winter School on Theor Physics
An oscillating Universe which arises from the linearized R
2 theory of gravity is discussed, showing that some observative evidences like the cosmological redshift and the Hubble law are in agreement with the model. In this context Dark Energy is seen like a pure curvature effect arising by the Ricci scalar.
In the general picture of high order theories of gravity, recently, the R^-1 theory has been analyzed in two different frameworks. In this letter a third context is added, considering an explicit coupling between the R^-1 function of the Ricci scalar and the matter Lagrangian. The result is a non-geodesic motion of test particles which, in principle, could be connected with Dark Matter and Pioneer anomaly problems.
After a review of the frequency - dependent angular pattern of interferometers in the TT gauge for scalar gravitational waves (SGWs), which has been recently analysed by Capozziello and Corda, in this letter the result is used to study the cross correlation between the Virgo interferometer and the MiniGRAIL resonant sphere. It is shown that the overlap reduction function for the cross correlation bewteen Virgo and the monopole mode of MiniGRAIL is very small, but a maximum is also found in the correlation at about 2710Hz, in the range of the MiniGRAIL sensitivity
A solution of linearized Einstein field equations in vacuum is given and discussed. First it is shown that, computing from our particular metric the linearized connections, the linearized Riemann tensor and the linearized Ricci tensor, the linearized Ricci tensor results equal to zero. Then the effect on test masses of our solution, which is a gravitational wave, is discussed. In our solution test masses have an apparent motion in the direction of propagation of the wave, while in the transverse direction they appear at rest. In this way it is possible to think that gravitational waves would be longitudinal waves, but, from careful investigation of this solution, it is shown that the tidal forces associated with gravitational waves act along the directions orthogonal to the direction of propagation of waves. The computation is first made in the long wavelengths approximation (wavelength much larger than the linear distances between test masses), then the analysis is generalized to all gravitational waves. In the last sections of this paper it is shown that the frequency dependent angular pattern of interferometers can be obtained from our solution and the total signal seen from an interferometer for the stochastic background of gravitational waves is computed.
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