Дисертації з теми "Espace-temps quantiques"
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Décanini, Yves. "Phénomènes de résonance et renormalisation en espace-temps courbe." Habilitation à diriger des recherches, Université Pascal Paoli, 2008. http://tel.archives-ouvertes.fr/tel-00609537.
Bogdanoff, Grichka. "Fluctuations quantiques de la signature de la métrique à l'échelle de Planck." Dijon, 1999. https://tel.archives-ouvertes.fr/tel-00001502.
XAVIER, GUIMARAES MARIA EMILIA. "Contributions a l'etude des champs quantiques en espace-temps conique et des solutions de type vortex couplees a la gravitation." Paris 6, 1996. http://www.theses.fr/1996PA066436.
Josset, Thibaut. "Vers une formulation covariante de la mécanique statistique." Thesis, Aix-Marseille, 2017. http://www.theses.fr/2017AIXM0272.
According to general relativity, spacetime is not the absolute arena that Newton had imagined, where particles move, are created or annihilated. Instead, it is a dynamical object identified with the gravitational field, that possesses its own local degrees of freedom and, as such, can be subject to thermal fluctuations. A better understanding of the statistical properties of these local fluctuations would be highly relevant for early cosmology, quantum gravity, or the study of black holes. Unfortunately, the application of statistical mechanics ideas to relativistic systems faces a major conceptual difficulty: the absence of a preferred time. In this thesis, we present three approaches to covariant statistical mechanics. First, the thermal time hypothesis reverses the common logic and proposes the existence of a preferred time to be subsequent to the actual state of the system. An alternative path consists in extending the ergodic hypothesis of standard statistical mechanics to include time averages performed using internal clocks. Lastly, the idea that thermodynamics could find its origin at the microscopic scale in the entanglement of quantum systems is studied, the statistical state being then determined by the structure of the Hilbert space. In all cases, the notion of subsystem appears as the essential element to achieve a covariant formulation of statistical mechanics
Durbec, Amélia. "Dynamiques causales de graphes réversibles et quantiques." Electronic Thesis or Diss., Aix-Marseille, 2022. http://www.theses.fr/2022AIXM0459.
Causal graph dynamics are a twofold extension of cellular automata: the underlying grid is extended to an arbitrary graph of bounded degree and the graph itself can evolve in time.In the reversible regime, we prove that causal graph dynamics can be reversible while creating/destroying vertices, through three different models that we prove to be equivalent.Based on these results, we exhibit causal dynamics that are both reversible and increasing in space, which brings new insights into the compatibility between the time arrow and reversibility. We define a notion of graph subshifts, which can be used to study causal dynamics of graphs by unifying temporal and spatial dimensions, in the same way that 1D cellular automata can be studied with 2D subshifts of finite type.In the quantum regime, our first contribution is to provide a rigorous definition of state space. A notable question was whether vertex names are necessary; we prove they are indeed necessary in order to prevent faster-than-light signaling. We also point out that renaming on graphs is the natively discrete analog of coordinate changes
Jian, Pu. "Limites quantiques dans les mesures de distance à l'aide de peignes de fréquences." Thesis, Paris 6, 2014. http://www.theses.fr/2014PA066574.
In many fields of physics, the determination of the space-time position of an object is performed at high levels of accuracy and precision by the exchange of light pulses. In this thesis, we investigate the quantum limits in a parameter estimation scheme using light in a practical point of view, and we study how these limits apply in a range-finding scheme using optical frequency combs. In a first part, we study the quantum limits in a general parameter estimation problem by the means of the quantum Cramér-Rao bound. We focus on schemes involving multimode Gaussian states and derive the limits of sensitivity in the estimation of any parameter encoded in such states. We show that a simple experimental setup allows to optimally measure the parameter carried by the light. In a second part, we study how these limits apply in a range-finding protocol using optical frequency combs. In a well-controlled environment such as vacuum, we show that there exists an optimal scheme, requiring pulse shaping techniques, which sensitivity is better than the usual phase interferometry and time-of-flight measurements. We present experimental results that exhibits the standard quantum limit in space-time positioning. In the last part, we study the limitations introduced to this optimal scheme when the environment is weakly dispersive, like in air. We demonstrate that the loss of accuracy caused by such environmental fluctuations can be compensated at the expense of a reduced sensitivity. We propose an experimental scheme that allows to perform a real-time ranging measurement immune from atmospheric perturbations, without any knowledge of the values of the environmental parameters
Ben, Cheikh Harrek Zouhour. "Étude des ondes de spin dans des puits quantiques CdMnTe." Thesis, Montpellier 2, 2013. http://www.theses.fr/2013MON20071/document.
This thesis focuses on the study of spin waves in n-doped CdMnTe quantum wells using respectively time-resolved Kerr rotation (TRKR) and four-wave mixing (FWM) techniques. We studied three high mobility samples with different characteristics.The TRKR technique gives access only to zero wave vector excitations, in our case the spin- flip wave q = 0 . We studied the anticrossing that appears between the spin -flip wave and the manganese spin -flip excitation. We studied the gap variation energy between these modes as function on the power excitation and the magnetic field. In particular, we have extended the measurements of mixed modes at lower Mn concentration (up 0.07 %) and contrary to what were expected; we found that the strong coupling regime persists at this concentration.We are then interested in determining the two dimensional electron gas spin polarization ζ, which can be deduced from the energy coupling between the mixed modes. We found that the measured polarization exceeds the theoretical polarization calculated taking into account the increased susceptibility by many-body effects. We also measured the electron spin relaxation time and we have shown that it is influenced by thermal effects inherent to optical pump-probe experiments on this time.In the second part of this thesis, we studied by FWM the damping and the dispersion of the non-zero wave vector spin waves for one of our samples. We have demonstrated that we can actually generate spin waves in femtosecond excitation and deted them by FWM. We found that the dispersion is lower than that observed in the Raman experiments. This low dispersion may be due to the strong excitation density used in the FWM experiments (typically three to four orders of magnitude higher than the Raman ones) and / or the fact that two waves of wave vector q and - q, having different dispersions are simultaneously probed in FWM
Hersent, Kilian. "Field theories on quantum space-times : towards the phenomenology of quantum gravity." Electronic Thesis or Diss., université Paris-Saclay, 2024. http://www.theses.fr/2024UPASP031.
Noncommutative geometry is a mathematical framework that expresses the structure of space-time in terms of operator algebras. By using the tools of quantum mechanics to describe the geometry, noncommutative space-times are expected to give rise to quantum gravity effects, at least in some regime. This manuscript focuses on the physical aspects of these so-called quantum space-times, in particular through the formalism of field and gauge theories. Scalar field theories are shown to possibly trigger mixed divergences in the infra-red and ultra-violet for the 2-point function at one loop. This phenomenon is generically called UV/IR mixing and stems from a diverging behaviour of the propagator. The analysis of such divergences differs from the commutative case because the momentum space is now also noncommutative. From another perspective, a gauge theory on κ-Minkowski, a quantum deformation of the Minkowski space-time, is derived. A first perturbative computation is shown to break the gauge invariance, a pathological behaviour common to other quantum space-times. A causality toy model is also developed on κ-Minkowski, in which an analogue of the speed-of-light limit emerges. The phenomenology of quantum gravity arising from quantum space-times is discussed, together with the actual constraints it imposes. Finally, a toy model for noncommutative gravity is tackled, using the former κ-Minkowski space-time to describe the tangent space. It necessitates the notion of noncommutative partition of unity specifically defined there
Viet, Dang Nguyen. "Renormalisation de la théorie quantique des champs en espace-temps courbes: une approche causale." Phd thesis, Université Paris-Diderot - Paris VII, 2013. http://tel.archives-ouvertes.fr/tel-00918759.
Queva, Julien. "Interaction en Espace-temps de de Sitter : sur quelques problèmes de quantification: en espace-temps de de Sitter et par états cohérents." Phd thesis, Université Paris-Diderot - Paris VII, 2009. http://tel.archives-ouvertes.fr/tel-00503186.
Queva, Julien. "Interaction en Espace-temps de de Sitter : sur quelques problèmes de quantification: en espace-temps de de Sitter et par états cohérents." Phd thesis, Paris 7, 2009. http://www.theses.fr/2009PA077066.
This manuscript is devoted to quantization problems in mathematical and theoretical physics. It is divided into two subjects: conformally invariant fields on de Sitter spacetime and quantization through coherent states. The first subject follows a comprehensive program of covariant quantization of fields in de Sitter spacetime, whose spirit is close to the Wightman axiomatic. We paid a particular attention to the quantization of fields that could be extended to the conformal group. We developed a geometric point of view enabling us to link fields on de Sitter and Minkowski spacetimes while keeping transparent the action of the conformal group. This geometric viewpoint led us to the expression of a new propagator for the vector potential. Finally, this approach allowed us to set up a general framework to compute higher rank conformally invariant tensors, in de Sitter space-time. The second subject deals with coherent states and their use in quantization problems. The particle in an infinite well is a toy model for this type of CS quantization since the momentum operator, in spite of being symmetric, is not self-adjoint and there is impossibility of canonical commutation rule (Pauli Theorem). Thanks to a new family of 2-component vector-valued coherent states, we were able, to quantize, in a consistent way, the particle in the infinite well. Finally, we began the fuzzyfication of the hyperboloid, that is the quantization of the de Sitter spacetime itself, through generalized coherent states
Stoskopf, Théo. "États de Hadamard pour des champs de Dirac en espace-temps courbe." Electronic Thesis or Diss., université Paris-Saclay, 2024. http://www.theses.fr/2024UPASM006.
This thesis is about applying microlocal techniques to the construction of Hadamard states for Dirac fields on curved spacetimes with weak conditions on their asymptotical behaviors. In a second time we will focus on the construction of in and out vacuum states and prove their Hadamard property
Folacci, Antoine. "Quantification des champs en espace-temps courbe et renormalisation du tenseur d'impulsion-énergie." Paris 11, 1988. http://www.theses.fr/1988PA112075.
Busch, Xavier. "Effets dispersifs et dissipatifs en théorie quantique des champs en espace-temps courbe pour modéliser des systèmes de matière condensée." Thesis, Paris 11, 2014. http://www.theses.fr/2014PA112205/document.
The two main predictions of quantum field theory in curved space-time, namely Hawking radiation and cosmological pair production, have not been directly tested and involve ultra high energy configurations. As a consequence, they should be considered with caution. Using the analogy with condensed matter systems put forward by Unruh, their analogue versions could be tested in the lab. Moreover, the high energy behavior of these systems is known and involved dispersion and dissipation, which regulate the theory at short distances. When considering experiments which aim to test the above predictions, the thermal noise will contaminate the outcome. Indeed, there will be a competition between the stimulated emission from thermal noise and the spontaneous emission out of vacuum. In order to measure the quantum analogue Hawking radiation, or the analogue pair production also called dynamical Casimir effect, one should thus compute the consequences of ultraviolet dispersion and dissipation, and identify observables able to establish that the spontaneous emission took place. In this thesis, we first analyze the effects of dispersion and dissipation on both Hawking radiation and pair particle production. To get explicit results, we work in the context of de Sitter space. Using the extended symmetries of the theory in such a background, exact results are obtained. These are then transposed to the context of black holes using the correspondence between de Sitter space and the black hole near horizon region. To introduce dissipation, we consider an exactly solvable model producing any decay rate. In such a model, the field is linearly coupled to an environment containing a dense set of degrees of freedom. We also study the quantum entanglement of the particles so produced. In a second part, we consider explicit condensed matter systems, namely Bose Einstein condensates and exciton-polariton systems. We analyze the effects of dissipation on entanglement produced by the dynamical Casimir effect. As a final step, we study the entanglement of Hawking radiation in the presence of dispersion for a generic analogue system
Mondragơn, Lopez Mauricio Javier. "Probabilité des événements multiples dans la mécanique quantique relativiste-générale et quelques aspects qualitatifs ("philosophiques") sur l'espace et le temps." Aix-Marseille 2, 2008. http://www.theses.fr/2008AIX22017.
Ruffin-Bayardin, Céline. "Le présent : entre physique et philosophie. Vers un présentisme quantique." Thesis, Université de Paris (2019-....), 2019. http://www.theses.fr/2019UNIP7005.
It would seem from Einstein's words that physics fails to capture the singularity of the Now. In this research, we are interested in what makes the present special : how is the present different from the past and the future? Is it really inaccessible to physics? What is the nature of the relationship between the present and reality? Hence our problematic triangle articulated around real-present-physics notions. At first, we analyze the status of the present in classical physics, then from the current metaphysical debate on time, and more particularly from linguistics and modal logic, we question the reality of the present. This leads us to approach theories such as the Presentism, the Growing Block, or the Branching-Futurism. The question of the existence of the present also requires for us the study of the "problem of time" in quantum gravity. Finally, in a third and last part, we construct Quantum Presentism. For this, we use Gilbert Simondon's method, and we deal with the singularity of the present from the very process of individuation of the present
Dang, Nguyen Viet. "Renormalization of quantum field theory on curved space-times, a causal approach." Paris 7, 2013. http://www.theses.fr/2013PA077188.
The subject of the thesis is the construction of a perturbative quantum theory of interacting fields on a curved space-time, following a point of view pioneered by Stueckelberg and Bogoliubov and developed by Epstein-Glaser on the flat Minkowski space-time. In 2000 a breakthrough was done by Brunetti and Fredenhagen who were able to extend the Epstein-Glaser theory by exploiting the point of view developed by Radzikowski to define quantum states on a curved space-time in terms of wave-front sets. These results were further extended by Fredenhagen, Brunetti, Hollands, Wald, Rejzner, etc. To Yang-Mills fields and the gravitation. However, even for theories without gauge invariance, many mathematical details were left unexplored and unquestioned. The task of Viet was precisely to derive fully rigorously this theory in the case there is no gauge invariance. In my work, I propose a complete review of the result, solving numerous questions, adding many new results around this program and, eventually, giving more precise details on the counterterms and ambiguities in the renormalization process, and a deeper understanding of the geometry of the wave front set of the n-point functions. All this thesis uses various mathematical techniques: differential and pseudo Riemannian geometry, microlocal analysis and the symplectic geometry of wavefront sets, functional analysis, fine results from the theory of distributions, Hopf algebras, etc
Grinbaum, Alexei. "Le rôle de l'information dans la théorie quantique." Phd thesis, Ecole Polytechnique X, 2004. http://tel.archives-ouvertes.fr/tel-00007634.
Renaud, Jacques. "Contribution à l'étude mathématique de la quantification et des contractions : courbure, vitesse de la lumière, masse et constante de Planck." Paris 7, 1994. http://www.theses.fr/1994PA077083.
Guilleux, Maxime. "The nonperturbative renormalization group for quantum field theory in de De Sitter space." Thesis, Sorbonne Paris Cité, 2016. http://www.theses.fr/2016USPCC141/document.
The nonperturbative renormalization group for quantum field theory in de Sitter space.The study of cosmology draws us to the topic of quantum fields in curved space-time. In particular, light scalar fields offer a simple mechanism for inflation and primordial fluctuations. When computing loop corrections to these models however, infrared and secular divergences appear which call for resummation techniques. To this end, we implement the nonperturbative renormalization group for quantum scalar fields on a fixed de Sitter background. First, the Local Potential Approximation (LPA) is applied. We show that there is always symmetry restoration due to infrared effects, and that mass is generated in agreement with the stochastic approach. Next, we study the flat space limit of our formalism by taking the curvature $H\to0$, and we check that it reproduces a number of known results. Finally, we discuss the derivative expansion, which goes beyond the LPA. Its implementation seems too complex in general curved space-times, but de Sitter symmetries allow for a simpler representation. We define a prescription for all orders of the expansion, and discuss the flow of the first order term in the simple case where we neglect the field dependency (LPA')
De, Lorenzo Tommaso. "Black holes as a gateway to the quantum : classical and semi-classical explorations." Thesis, Aix-Marseille, 2018. http://www.theses.fr/2018AIXM0264/document.
Since 1916 intriguing questions have arisen from the study of Black Holes (BH). Only some of them have been resolved. Indeed, we are faced with regimes where the yet unknown interplay between quantum theory and spacetime unveils. BH physics is a gateway to the quantum nature of gravity. My thesis has been completely devoted to this central domain of theoretical physics, with the guiding aim of understanding in the widest possible manner the debate around those questions. The process has produced original results that constitute the main core of the manuscript. 1- The maximal volume surfaces of evaporating BHs are studied. An astrophysical BH will end its life with an external planckian area $10^{-70} m^2$ hiding $10^5$ times the volume of our observable Universe. This can have consequences on the viability of the “remnant scenario” as solution to the BH information paradox. 2- The “black-hole-to-white-hole scenario” is analyzed. The model is shown to be strongly unstable, and a minimal resolutive modification is proposed. 3- A generalisation of the four laws of BH thermodynamics is proven for intersecting light cones in Minkowski spacetime. 4- Conformally flat spaces where such laws acquire the standard thermodynamical interpretation are studied. The simplest one is the Bertotti-Robinson spacetime, known to encode the near-horizon geometry of a charged BH. 5- It is shown that, if the correct energy-momentum tensor is identified, the Eintein-Cartan’s field equations can be recovered as a thermodynamical equilibrium equation of state just like in the GR original case. Such results contribute to the intense debate on the opening crucial questions
Troessaert, Cédric. "Aspects of duality in gravitational theories." Doctoral thesis, Universite Libre de Bruxelles, 2011. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/209892.
Un des outils pour étudier une theorie est la notion de dualité. On dit que deux théories sont duales quand elles décrivent le même système par des moyens différents. La dualité est le dictionnaire permettant de passer d’une description à l’autre. Dans ma thèse, j’ai étudié deux dualités s’appliquant à la gravité en 4 dimensions.
La première est connue sous le nom de dualité électromagnétique. A l’origine, cette dualité s’applique à l’électromagnétisme où elle échange les rôles du champ &
Doctorat en Sciences
info:eu-repo/semantics/nonPublished
Brunswic, Léo. "Surfaces de Cauchy polyédrales des espaces temps plats singuliers." Thesis, Avignon, 2017. http://www.theses.fr/2017AVIG0420/document.
The study of singular flat spacetimes with polyhedral Cauchy-surfaces is motivated by the quantum gravity toy model role they play in the seminal work of Deser, Jackiw and 'T Hooft. This thesis study parametrisations of classes of singular flat spacetimes : Cauchy-compact maximal flat spacetimes with massive and BTZ-like singularities. Two parametrisations are constructed. The first is based on an extension of Mess theorem to flat spacetimes with BTZ and Penner-Epstein convex hull construction. The second is based on a generalisation of Alexandrov polyhedron theorem to radiant Cauchy-compact flat spacetimes with massive and BTZ-like singularities. This work also initiate a wider theoretical background that encompass singular spacetimes
Perenon, Louis. "Elements of phenomenology of dark energy." Thesis, Aix-Marseille, 2017. http://www.theses.fr/2017AIXM0284/document.
The ΛCDM paradigm is the standard model of cosmology. In this model, the universe is constituted today for the major part by Cold Dark Matter along with the Cosmological Constant Λ that drives cosmic acceleration. However, this standard model is not fully complete. Using the Cosmological Constant introduces theoretical issues in a quantum field theory description and tentative observational evidences suggests our large scale description of the universe should be refined. Finding alternatives to the standard model is therefore of crucial importance today
Lamy, Frédéric. "Theoretical and phenomenological aspects of non-singular black holes." Thesis, Sorbonne Paris Cité, 2018. http://www.theses.fr/2018USPCC203/document.
The issue of singularities in General Relativity dates back to the very first solution to the equations of the theory, namely Schwarzschild's 1915 black hole. Whether they be of coordinate or curvature nature, these singularities have long puzzled physicists, who managed to better characterize them in the late 60's. This led to the famous singularity theorems applying both to cosmology and black holes, and which assume a classical behaviour of the matter content of spacetime summarized in the so-called energy conditions. The violation of these conditions by quantum phenomena supports the idea that singularities are to be seen as a limitation of General Relativity, and would be cured in a more general theory of quantum gravity. In this thesis, pending for such a theory, we aim at investigating black hole spacetimes deprived of any singularity as well as their observational consequences. To that purpose, we consider both modifications of General Relativity and the coupling of Einstein's theory to exotic matter contents. In the first case, we show that one can recover the static spherically symmetric non-singular black holes of Bardeen and Hayward in principle in mimetic gravity, and implicitly by a deformation of General Relativity's hamiltonian constraint in an approach based on loop quantum gravity techniques. In the second case, we stay inside the framework of General Relativity and consider effective energy-momentum tensors associated with a fully regular rotating Hayward metric and with a dynamical spacetime describing the formation and evaporation of a non-singular black hole. For the latter, we show that all models based on the collapse of ingoing null shells and willing to describe Hawking’s evaporation are doomed to violate the energy conditions in a non-compact region of spacetime. Lastly, the theoretical study of the rotating Hayward metric comes with numerical simulations of such an object at the center of the Milky Way, using the ray-tracing code Gyoto and mimicking the known properties of the accretion structure of Sgr A*. These simulations allow exhibiting the two very different regimes of the metric, with or without horizon, and emphasize the difficulty of asserting the presence of a horizon from strong-field images as the ones provided by the Event Horizon Telescope