Literatura científica selecionada sobre o tema "Scalaire-Tenseur"
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Teses / dissertações sobre o assunto "Scalaire-Tenseur"
NOVAK, JEROME. "Etude numerique de sources de rayonnement gravitationnel en theorie tenseur-scalaire de la gravite". Paris 7, 1998. http://www.theses.fr/1998PA077115.
Texto completo da fonteJulié, Félix-Louis. "Sur le problème à deux corps et le rayonnement gravitationnel en théories scalaire-tenseur et Einstein-Maxwell-dilaton". Thesis, Sorbonne Paris Cité, 2018. http://www.theses.fr/2018USPCC131/document.
Texto completo da fonteWith the birth of "gravitational wave astronomy" comes the opportunity to test general relativity and its alternatives in a strong field regime that had never been observed so far: that of the coalescence of a compact binary sytem. This thesis studies the problem of motion and gravitational radiation from such systems in modified gravities, by adapting some of the key analytical tools that were first developed in the context of general relativity. First, we show how to widen the "effective-one-body" (EOB) formalism to a large class of modified gravities, including, e.g., scalar-tensor theories. In the latter, the gravitational interaction is described by supplementing general relativity with a (massless) scalar degree of freedom. The corresponding two-body lagrangian being known at post-post-keplerian order, we build an associated EOB hamiltonian, which describes the motion of a test particle orbiting in effective external fields. This enables to simplify and resum the two-body dynamics; and hence, to explore the strong-field regime near merger. We then "tackle", for the first time, the analytical description of "hairy" binary black hole systems, and obtain their (EOB) gravitational waveform counterparts in Einstein-Maxwell-dilaton theories, which generalize scalar-tensor theories by means of a (massless) vector field. To that end, we derive the two-body lagrangian at post-keplerian order as well as the energy flux radiated at infinity at quadrupolar order. As in general relativity, our developments rely on the phenomenological description of the black hole’s trajectories as worldlines of point particles that are, in turn, described by a "skeleton" action generalizing that of general relativity. Finally, we develop a formalism based on Katz’ "superpotentials" to define the mass (as a nœther charge) of a black hole that is endowed with vector and scalar "hair". We then deduce the first law of thermodynamics, which is particularly suitable to describe its readjustments when interacting with a faraway companion. Black hole thermodynamics is lastly shown to be a powerful tool to interpret and discuss the scope of their "skeletonization"
Lehebel, Antoine. "Objets astrophysiques compacts en gravité modifiée". Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLS204/document.
Texto completo da fonteTwenty years have passed since the discovery of the accelerated expansion of the Universe, reviving the interest for alternative theories of gravity. Adding a scalar degree of freedom to the usual metric of general relativity is one of the simplest ways to modify our gravitational theory. In parallel, our knowledge about black holes and neutron stars is booming, notably thanks to the advent of gravitational wave astronomy. This thesis is at the crossroads between the two fields, investigating the properties of compact objects in extended scalar-tensor theories. I start by reviewing essential no-hair results established since the seventies. After discussing the no-hair theorem proposed for black holes in Horndeski theory, I present its extension to stars. The second part of the thesis investigates in detail the various ways to circumvent this theorem. These notably include solutions with a time-dependent scalar field in order to match cosmological evolution, but also static and asymptotically flat configurations. In a third part, I establish an important stability criterion for these solutions, based on their causal structure. It is also the occasion to study the propagation of gravitational waves in black hole environments, and to select the theories where gravitational waves travel at the same speed as light
Larena, Julien. "Champs scalaires en cosmologie : discussions sur les principes d'équivalence et cosmologique". Phd thesis, Université Paris-Diderot - Paris VII, 2007. http://tel.archives-ouvertes.fr/tel-00185582.
Texto completo da fonteEn lien avec le problème de l'énergie sombre, cette thèse se propose d'explorer, à travers les propriétés dynamiques de champs scalaires, deux principes qui se trouvent au coeur de la cosmologie: les principes d'équivalence et cosmologique.
Le principe d'équivalence est abordé à travers les théories scalaire-tenseur de la gravité, permettant d'intégrer la Relativité Générale dans un cadre large de théories respectant la version faible du principe d'équivalence tout en permettant de tester sa version forte. Dans cette perspective, les propriétés dynamiques et les conséquences cosmologiques de ces théories sont discutées.
Le principe cosmologique quant à lui est reformulé; ses contours sont redéfinis, menant à la formulation de modèles cosmologiques différents du modèle standard, par le biais des cosmologies inhomogènes moyennées. Ces modèles permettent de prendre en compte de façon consistante la structuration à petites échelles de l'Univers et son homogénéité aux grandes échelles, ouvrant ainsi la possibilité d'expliquer l'énergie sombre par la formation des structures; il est également possible de les mettre en correspondance avec l'apparition de champs scalaires dans le cadre du modèle standard.
Cipriano, Francesco. "Recherche de matière noire scalaire légère avec des détecteurs d'ondes gravitationnelles". Thesis, Université Côte d'Azur, 2020. http://www.theses.fr/2020COAZ4040.
Texto completo da fonteThe existence of the dark matter and the truth beyond its nature has been one of the greatest puzzles of the twentieth century and still it is nowadays. In the last decades several hypotheses, such as the WIMPs model, have been proposed to solve such puzzle but none of them has been able so far to succeed.In this thesis work we will focus on another very appealing model in which dark matter is successfully described by an ultra-light scalar field whose origin can be sought in the low-energy limit of one of the most promising unification theories: the String Theory.In this work we show how such scalar field, if present, interacts with standard matter and in particular with the optical apparatus that is at the core of gravitational waves antennas. We derive and discuss the signal produced by this interaction through different approaches deriving both approximated and exact solutions. Special attention is paid to the second-order term of the signal approximate series expansion whose contribution ends up to be not negligible when one factors in the specific geometrical dimensions and frequency range of gravitational waves detectors like Advanced LIGO and Advanced Virgo.A suggested by recent surveys we assume presence of a dark matter stream in the local neighborhood of the solar system and show its effect on the signal.We then propose and discuss a hierarchical statistical analysis aimed to the signal detection. In case of no detection a limit curve for the coupling parameter dg* is derived. Such curve is then analyzed in detail showing the magnitude of the contribution of the first-order and second-order terms of the signal series expansion. We analyze the modification of the constraint curve due to the variation of the fraction of local dark matter belonging to the stream. We show finally how the constraint curve responds to variations of the search parameter and discuss the optimal choices
Ranquet, André. "Sur certaines propriétés de l'Energie Noire". Thesis, Montpellier 2, 2010. http://www.theses.fr/2010MON20201.
Texto completo da fonteThe results of the cosmological observations at the turn of the century (SN1a, CMB, BAO) show that, in contrast to the predictions of the standard model, the Universe expansion is presently accelerating. To account for this fact, an unknown component dubbed "dark energy" was introduced either directly as a fluid with negative pressure, or indirectly as a modification of General Relativity.After the presentation of the general frame of the Universe description, and of the presently accepted cosmological standard model, we study the interactions between dark energy and a possible spatial curvature, with special attention to the cases where the curvature uncertainty may falsify the phantom nature of dark energy. In a second step we consider a modification of General Relativity, the Scalar-Tensor theories, as a way to generate dark energy. The general viability conditions for these theories are presented, as well as the conditions for the presence of normal and phantom dark energy. In particular we study the possibility to detect this Scalar-Tensor dark energy with measurements within the Solar System using the Parametrised Post-Newtonian formalism
Cluzel, Emeline. "Inflation en cosmologie des cordes". Phd thesis, Ecole Polytechnique X, 2011. http://pastel.archives-ouvertes.fr/pastel-00653149.
Texto completo da fonteLecoeur, Nicolas. "Exact black hole solutions in scalar-tensor theories". Electronic Thesis or Diss., université Paris-Saclay, 2024. http://www.theses.fr/2024UPASP036.
Texto completo da fonteGeneral Relativity allows for a unique black hole solution, characterized by its mass M, angular momentum J, and electric charge Q. Black holes in General Relativity are thus said to have no hair, that is, no other independent physical quantity (no-hair theorem).Despite the numerous successes of General Relativity, some limitations remain, like the central singularity possessed by black holes, where the curvature of spacetime becomes infinite. Modified theories of gravity try to solve some of these shortcomings.This thesis tests the no-hair theorem in a popular modification of gravity, called scalar-tensor theories, where a unique degree of freedom (a scalar field) is added on top of the usual metric of spacetime of General Relativity. Using various symmetries, new black holes, called hairy black holes, are obtained. Some of them evade strongly the no-hair theorem, being characterized by a new quantity, distinct from M, J or Q. An interesting progress is also achieved, since in certain cases, the usual singularity disappears: the curvature of spacetime remains bounded even at the core of the black hole. Moreover, theoretical links are established between scalar-tensor theories (which take place in the usual four dimensions of spacetime), and theories of gravity in higher dimensions. Finally, certain particular properties of scalar-tensor theories enable to transform initial black hole solutions into other solutions with very distinct geometry, like wormholes
Fay, Stéphane. "Cosmologies spatialement homogènes en théories tenseur-scalaires". Phd thesis, Université Paris-Diderot - Paris VII, 2004. http://tel.archives-ouvertes.fr/tel-00008063.
Texto completo da fonteGannouji, Radouane. "Les mystères de l'expansion accélérée de l'univers". Phd thesis, Montpellier 2, 2008. http://www.theses.fr/2008MON20068.
Texto completo da fonteSeveral steps were necessary for the construction of the standard model of cosmology, the vision of our universe, the representation of the infinity. Since 1915 with Einstein's formulation of general relativity, various observations of the Universe have led to imagine an expanding decelerated universe. However, in 1998, two U. S. Teams pointed out an acceleration. This fact was largely confirmed since then. This raises a simple question, what is the reason for this recent acceleration of the universe? Many models of dark energy were developed in order to answer this question. I address in this thesis two major models. The first model is scalar-tensor theories where a scalar field is coupled to the graviton. Various constraints were built on the local viability of this model. Similarly, we have studied the f(R) theories. The construction in these models of the function m(r) gives us a simple and elegant method to describe the cosmological evolution of the universe implied by such lagrangians. Many models previously studied were rejected because they do not have a matter phase. Finally we study the growth of matter perturbations. Indeed the perturbations at the origin of large scale structures will grow differently according to the model and the universe considered. We have thus shown a very important distinction between models of dark energy in general relativity and scalar-tensor theories. More precise observations will enable to distinguish models of dark energy in general relativity and modified gravity