Дисертації з теми "Phénoménologie de la gravité quantique"
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Linsefors, Linda. "Phénoménologie de la cosmologie quantique à boucles." Thesis, Université Grenoble Alpes (ComUE), 2016. http://www.theses.fr/2016GREAY009/document.
Loop quantum gravity (LQG) is an attempt to solve the problem of quantum gravity. Loop quantum cosmology (LQC) is an attempt to apply LQG to early cosmology. The purpose of LQC is to connect LQG with observations. It is very hard to observe any quantum gravity effects because enormous energy density is most likely required. This is exactly why the early Universe is chosen as a stage to search for quantum gravity phenomena.The central result of LQC is that the big bang singularity is replaced by a big bounce. However this is not something that is possible to observe today. For this reason, we have investigated how cosmic perturbations are affected by LQC. We have used the so called deformed algebra approach, and have calculated the resulting spectrums for both scalar and tensor perturbations.The spectrums that we have found are not compatible with observation. However this can not bee taken as very strong evidence against LQG since there are too many assumptions on the way. Rather this is a result for this specific interpretation of LQC.We have also studied the background dynamics (the homogenous part of the equations) of LQC. Since slow-roll inflation is essential in explaining many features of the universe, including the CMB, we want to know if slow-roll inflation is compatible with LQC. We have found that, indeed, it is. If a square potential inflation field is added to the theory, the bounce will lift the potential energy enough to provide around 145 e-folds of slow-roll inflation. However, when anisotropies are taken into account, the amount of inflation decreases, and can even disappear completely if there is too much shear at the time of the bounce.We have derived the modified Friedman equation for anisotropic LQC. This has allowed us to study anisotropic LQC not just numerically, but also analytically, which has given us a much more comprehensive understanding of the situation than what was known before.Finally, we have studied some geometric aspects of de Sitter space, which has resulted in two very different considerations. Firstly we found that we can, for a general theory of modified cosmology and under some quite conservative assumptions, derive the dynamics for a spatially curved universe, given the dynamics of a spatially flat one. This is relevant in theories such as LQC, where it is easier to find the flat solution than the curved one. Secondly, we propose a possible mechanism for the origin and rebirth of the Universe
Coutant, Antonin. "phénoménologie de la gravité quantique : Propriété de stabilité de la radiation d'Hawking en présence de violation de l'invariance local de Lorentz." Phd thesis, Université Paris Sud - Paris XI, 2012. http://tel.archives-ouvertes.fr/tel-00747874.
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
Girelli, Florian. "Géométrie non commutative et gravité quantique." Aix-Marseille 1, 2002. http://www.theses.fr/2002AIX11039.
Zhang, Mingyi. "Gravité quantique à boucles et géométrie discrète." Thesis, Aix-Marseille, 2014. http://www.theses.fr/2014AIXM4027/document.
In this thesis, I will present how to extract discrete geometries of space-time fromthe covariant formulation of loop quantum gravity (LQG), which is called the spinfoam formalism. LQG is a quantum theory of gravity that non-perturbative quantizesgeneral relativity independent from a fix background. It predicts that the geometryof space is quantized, in which area and volume can only take discrete value. Thekinematical Hilbert space is spanned by Penrose's spin network functions. The excita-tion of geometry can be neatly visualized as fuzzy polyhedra that glued through theirfacets. The spin foam defines the dynamics of LQG by a spin foam amplitude on acellular complex, bounded by the spin network states. There are three main results inthis thesis. First, the semiclassical limit of the spin foam amplitude on an arbitrarysimplicial cellular complex with boundary is studied completely. The classical discretegeometry of space-time is reconstructed and classified by the critical configurations ofthe spin foam amplitude. Second, the three-point function from LQG is calculated.It coincides with the results from discrete gravity. Third, the description of discretegeometries of null hypersurfaces is explored in the context of LQG. In particular, thenull geometry is described by a Euclidean singular structure on the two-dimensionalspacelike surface defined by a foliation of space-time by null hypersurfaces. Its quan-tization is U(1) spin network states which are embedded nontrivially in the unitaryirreducible representations of the Lorentz group
Wieland, Wolfgang. "Structure chirale de la gravité quantique à boucles." Thesis, Aix-Marseille, 2013. http://www.theses.fr/2013AIXM4094/document.
General relativity is the most precise theory of the gravitational interaction. It is a classical field theory. All matter, on the other hand, follows the rules of quantum theory. At the Planck scale, at about distances of the order of 10E-35 meters, both theories become equally important. Today, theoretical physics lacks a unifying language to explore what happens at this scale, but there are several candidate theories available. Loop quantum gravity is one them, and it is the main topic of this thesis. To see whether a particular proposal is a viable candidate for a quantum theory of the gravitational field it must be free of internal inconsistencies, and agree with all experimental tests of general relativity. This thesis develops mathematical tools to check these
Christodoulou, Marios. "Transition de géométrie en gravité quantique à boucles covariante." Thesis, Aix-Marseille, 2017. http://www.theses.fr/2017AIXM0273.
In this manuscript we present a calculation from covariant Loop Quantum Gravity, of a physical observable in a non-perturbative quantum gravitational physical process. The process regards the transition of a trapped region to an anti--trapped region and is treated as a quantum geometry transition akin to gravitational tunneling. The physical observable is the characteristic timescale in which the process takes place. We start with a top--to--bottom formal derivation of the ansatz defining the amplitudes for covariant LQG, starting from the Hilbert-Einstein action. We then take the bottom--to--top path, starting from the EPRL ansatz, to the sum--over--geometries path integral emerging in the semi-classical limit, and discuss its close relation to the naive path integral over the Regge action. We proceed to the construction of wave--packets describing quantum spacelike three-geometries that include a notion of embedding in a Lorentzian spacetime. We derive a simple estimation for the amplitudes describing geometry transition and show that a probabilistic description for such phenomena emerges, with the probability of the phenomena to take place being in general non-vanishing.The Haggard-Rovelli spacetime, modelling the spacetime surrounding the geometry transition region for a black to white hole process, is formulated. We then use the semi--classical approximation to give a general estimation of amplitudes describing the process. We conclude that the transition is predicted to be allowed by LQG, with a crossing time that is linear in the mass. The probability for the process to take place is suppressed but non-zero
Louapre, David. "Modèles de mousses de spin pour la gravité quantique en 3 dimensions." Phd thesis, Ecole normale supérieure de lyon - ENS LYON, 2004. http://tel.archives-ouvertes.fr/tel-00337352.
Noui, Karim. "Gravitation quantique et groupes quantiques." Montpellier 2, 2003. http://www.theses.fr/2003MON20080.
Regnault, Nicolas. "Solutions exactes de la gravité réduite : effet Hall quantique de spin." Phd thesis, Université Paris Sud - Paris XI, 2002. http://tel.archives-ouvertes.fr/tel-00001360.
Huang, Yichao. "Chaos multiplicatif gaussien et applications à la gravité quantique de Liouville." Thesis, Paris 6, 2017. http://www.theses.fr/2017PA066623/document.
In this thesis, we study the theory of Liouville Quantum Gravity via probabilist approach, introduced in the seminal paper of Polyakov in 1981, using path integral formalism on 2d surfaces. To define this path integral with exponential interaction, we started from the theory of Gaussian Multiplicative Chaos in order to define exponential of log-correlated Gaussian fields. In the first part, we generalise the construction of Liouville Quantum Gravity on the Riemann sphere to another geometry, the one of the unit disk. The novelty of this work, in collaboration with R.Rhodes and V.Vargas, is to analyse carefully the boundary term in the path integral formalism and its interaction with the bulk measure. We establish rigorously formulae from Conformal Field Theory in Physics, such as conformal covariance, KPZ relation, conformal anomaly and Seiberg bounds. A relaxed Seiberg bound in the unit volume case of Liouville Quantum Gravity on the disk is also announced and studied. In the second part of this thesis, we compare this construction in the spirit of Polyakov to another approach to the Liouville Quantum Gravity. In collaboration with two other young researchers, J.Aru and X.Sun, we give a correspondance between these two approaches in a simple but conceptually important case, namely the one on the Riemann sphere with three marked points. Using technics coming from these two approches, we give a new way of regularisation procedure that eventually allow us to link these two pictures
Esposito-Farèse, Gilles. "Théorie de Kaluza-Klein et gravitation quantique." Aix-Marseille 2, 1989. http://www.theses.fr/1989AIX22038.
Colosi, Daniele. "Sur certains aspects des approches canoniques et covariantes à la Gravité Quantique." Aix-Marseille 2, 2005. http://www.theses.fr/2005AIX22020.
De, Lacroix De Lavalette Corinne. "Gravité quantique à deux dimensions couplée à de la matière non-conforme." Thesis, Paris 6, 2017. http://www.theses.fr/2017PA066288/document.
Finding a theory of quantum gravity describing in a consistent way the quantum properties of matter and spacetime geometry is one of the greatest challenges of modern theoretical physics. However after several decades of research, many conceptual and technical issues are still to be resolved. Insights on these questions can be given by simplified toy models that allow for exact computations. The first part of the thesis deals with two-dimensional quantum gravity. In two dimensions quantum gravity is much better understood and many computations can be carried out exactly. Whereas two-dimensional quantum gravity coupled to conformal matter has been widely studied and is now well understood, much less was known until recently when matter is non-conformal. First we compute the gravitational action for a massive scalar field on a Riemann surface with boundaries and then for a massive Majorana fermion on a manifold without boundary. The latter case corresponds to a CFT perturbed by a conformal perturbation and is usually tackled through the DDK ansatz, but the results do not seem to match. Finally we give a minisuperspace computation of the spectrum of the Mabuchi action, a functional that appears in the gravitational action for a massive scalar field. In the second part we focus on black hole thermal behaviour which provides a lot of insight of how a theory of quantum gravity should look like. In the context of string theory the AdS/CFT correspondence provides powerful tools for understanding the microscopic origin of black holes thermodynamics. We construct a quantum mechanical toy model based on holographic principles to study the dynamics of quantum black holes
Pereira, Roberto. "Géométrie des simplexes et modèles de mousses de spin." Thesis, Aix-Marseille 2, 2010. http://www.theses.fr/2010AIX22024/document.
In this thesis we present a construction of the quantum amplitude associated to a Lorentzian 4-simplex, modifying a previous construction by Barrett and Crane. This 4-simplex amplitude is further used to construct a path integral defining a sum over simplicial geometries for a fixed triangulation of space-time. As a result we obtain a boundary state space given by spin-networks, establishing a connection between spin foams and Loop Quantum Gravity. Finally, we perform the semiclassical analysis for a single order is given by the exponential af the Regge action
D'Ambrosio, Fabio. "Semi-classical holomorphic transition amplitudes in covariant loop quantum gravity." Thesis, Aix-Marseille, 2019. http://theses.univ-amu.fr.lama.univ-amu.fr/190923_DAMBROSIO_92jrqgfl67z519ckyxxo477uxty_TH.pdf.
Covariant Loop Quantum Gravity (CLQG) is a tentative theory of quantum gravity which has emerged from a number of different research directions. Recently, it has been applied to the so-called black hole to white hole transition – a particular model of stellar collapse which resolves the information puzzle and potentially leads to observable effects. However, several conceptual and computational obstacles have impeded progress in the investigation of this physical scenario.This thesis addresses some of these issues: An integration measure for heat kernel states in the twisted geometry parametrization is derived which is necessary to define physical observables, a simplicial triangulation algorithm for manifolds of topology I x Σ is described and a new method is developed for computing holomorphic transition amplitudes in the absence of critical points. This new method can be seen as a semi-classical expansion of CLQG amplitudes around a classical background spacetime
Kouneiher, Joseph. "Etudes épistémologiques et histoire récente de la gravitation quantique." Paris 7, 1998. http://www.theses.fr/1998PA070119.
In the most recent reviews of quantum gravity it is acknowledged that there is as yet no successful and generally accepted framework for this discipline, despite the multitude of schemes for quantizing gravity that have been proposed since 1949. These schemes exhibit a remarkable variety of formally distinctive features, but epistemologically they all share one crucial feature: the problem of quantizing gravity is approached on purely formal grounds, as if it were a problem of mere mathematical technique which, once resolved, would automatically provide the solution to the plethora of foundational problems encountered by quantum general relativity. From a foundational perspective, however, the basic issues are not quite that simple. Our aim in this work is to reconsider the different attitudes and the thought processes involving in the quantum gravity subject from either epistemological and historical point of view. We show that the epistemological weakenesses of the conventional mode of thinking about these issues are well illustrated by the various treatements of the oldest scheme for quantizing gravity. We discuss the meaning of gravity, the quantum idea and the geometry behind. We analyse the geometric quantization program , we clarify the problems inherent in the two approaches of quantum gravity, the canonical and the covariant one. We review the limit of the application of general relativity and we inspect the question of observables, unitarity, causality and time in quantum gravity. Finally, we tried to elucidate the duality between general relativity and quantum mechanics
Cailleteau, Thomas. "Etude des perturbations cosmologiques et dérivation des observables en Gravité Quantique à Boucles." Phd thesis, Université de Grenoble, 2012. http://tel.archives-ouvertes.fr/tel-00749162.
Ruef, Clément. "Trous noirs en théorie des cordes : vers une compréhension de la gravité quantique." Phd thesis, Université Paris Sud - Paris XI, 2010. http://tel.archives-ouvertes.fr/tel-00518227.
Golubtsova, Anastasia. "Solutions exactes en théories de gravité et supergravité et les applications cosmologiques." Observatoire de Paris (1667-....), 2013. https://hal.science/tel-02095139.
For a D-dimensional gravitational model with a sigma-model source term, defined on a product of Einstein manifolds, the exact solutions of general type are generated using sigma model approach. The solutions are obtained in the following cases 1) when all factor spaces are Ricci-flat, 2) when one factor space has nonzero scalar curvature and other are Ricci-flat. For the first case we show that the solutions can describe the accelerated expansion of the Universe. A subclass of spherically-symmetric solutions is studied. "No-hair theorem" for black holes is proved. For the 4D model of the generalized Brans-Dicke gravity with scalar fields nonuniversally coupled to gravity, new solutions are found in terms of elliptic functions. We show that for certain parameters the solutions can be expressed in terms of exponential functions. Cosmological type solutions of supergravity origin are studied. A subslass of S-brane solutions corresponding to Lie algebras rank 3 is singled out, for which there exists a time interval where an accelerated expansion of a 3-dimensional subspace is compatible with a small enough value of the variation of the gravitational constant. For 11D N = 1 SUGRA orthogonal intersections of three M branes are studied. The explicit formulae for computing the amounts of preserved supersymmetries are obtained. Certain examples of the supersymmetric configurations containing such factor-spaces as K3, C²/Z², a four dimensional pp-waves manifold and R¹'¹/Z² are presented. We show that the replacement of the flat manifold with trivial topology by a Ricci-flat manifold of a flat manifold with non trivial topology reduces the number of preserved supersymmeties
Stagno, Gabriele Vittorio. "Quantum cosmology in loop quantum gravity : 2-vertex spinfoam amplitudes and effective hamiltonians." Thesis, Aix-Marseille, 2018. http://www.theses.fr/2018AIXM0190.
We first studied the transition amplitudes in loop quantum gravity (LQG) between two dipole spin-networks, as provided by the EPRL spinfoam model with 2 non-simplicial vertices. A systematic evaluation of these transition amplitudes has been discussed, identifying which ones were relevant for physical processes. Large scale spin behavior and correlations between the initial and final states has been evaluated, analytically for a simplified model and numerically for the full one, finding that the contributions of different graphs can be organized according to their behavior of setting to the scale in a hierarchy that is also preserved at small pirouettes and well captured already by a simplified model introduced.Beside, the effective quantum cosmological dynamics has been addressed for both isotropic and non isotropic models within the framework of Quantum reduced loop gravity (QRLG), a gauge fixed version of LQG. Dynamics has been addressed by means of a new regularization scheme based on states prepared in a superposition of graphs. New Hamiltonians have been computed, showing the usual regularization schemes introduced in loop quantum cosmology (LQC) naturally fit in this new scheme. Then we extended the domain of validity of our model to the non-isotropic case (Bianchi I spacetime). Both for isotropic and non isotropic cases, the new Hamiltonians generate a dynamics which is different from the one provided by LQC: in the isotropic case, the symmetric big bounce scenario is replaced by an evolution which is quasi stationary in the pre bounce phase and then follows the usual expansion. For Bianchi I an intriguing accelerated phase replaces the stationary one
Marquet, Cyrille. "Chromodynamique quantique à haute énergie, théorie et phénoménologie appliquée aux collisions de hadrons." Paris 6, 2006. https://tel.archives-ouvertes.fr/tel-00096416.
Dupuis, Maïté. "Modèles de mousses de spin pour la gravité quantique et leur régime semi-classique." Lyon, Ecole normale supérieure, 2010. http://www.theses.fr/2010ENSL0609.
The spinfoam framework is a proposal for a regularized path integral for quantum gravity. Spinfoams define quantum space-time structures describing the evolution in time of the spin network states for quantum geometry derived from Loop Quantum Gravity (LQG). The construction is based on the formulation of General Relativity as a topological theory plus the so-called simplicity constraints which introduce local degrees of freedom. In this PhD manuscript, an original way to impose the simplicity constraints in 4d Euclidean gravity using harmonic oscillators is proposed. A consistent spinfoam model for quantum gravity has to be connected to LQG and must have the right semi-classical limit. An explicit map between the spin network states of LQG and the boundary states of spinfoam models is given. New techniques to compute semiclassical asymptotic expressions for the transition amplitudes of 3d quantum gravity and to extract semi-classical information from a spinfoam model are introduced
Lemaire, Alexis. "Application de l'hypercalculie et de l'informatique quantique gravifique à l'intelligence artificielle générale." Reims, 2010. http://www.theses.fr/2010REIMS020.
Michel, Florent. "Effets non-linéaires et effets quantiques en gravité analogue." Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLS164/document.
The present thesis deals with some properties of classical and quantum scalar fields in an inhomogeneous and/or time-dependent background, focusing on models where the latter can be described as a curved space-time with an event horizon. While naturally formulated in a gravitational context, such models extend to many physical systems with an effective Lorentz invariance at low energy. We shall see how this effective symmetry allows one to relate the behavior of perturbations in these systems to black-hole physics, what are its limitations, and in which sense results thus obtained are “analogous” to their general relativistic counterparts. The first chapter serves as a general introduction. A few notions from Einstein's theory of gravity are introduced and a derivation of Hawking radiation is sketched. The correspondence with low-energy systems is then explained through three important examples. The next four chapters each details one of the works completed during this thesis, updated and slightly reorganized to account for new developments which occurred after their publication. The other articles I contributed to are summarized in the last chapter, before the general conclusion. My collaborators and I focused on three aspects of the behavior of fields close to the (analogue) event horizon in models with an effective low-energy Lorentz symmetry. The first one concerns nonlinear effects, which had been given little attention in view of their crucial importance for understanding the evolution in time of Hawking radiation as well as for experimental realizations. We showed in particular how they determine the late-time behavior in stable and unstable configurations. The second aspect concerns linear and quantum effects. We studied the Hawking radiation itself in several models and what replaces it when continuously erasing the horizon. We also characterized and classified the different types of linear instabilities which can occur. Finally, we contributed to the design and analysis of “analogue gravity” experiments in Bose-Einstein condensates, hydrodynamic flows, and acoustic setups, of which I report the main results
Geiller, Marc. "Gravité quantique à boucles, modèles de mousses de spins, et certains aspects de leur relation." Paris 7, 2012. http://www.theses.fr/2012PA077253.
In this PhD thesis, we study some aspects of the relationship between canonical loop quantum gravity and spin foam models. These models have been introduced as candidates for the covariant dynamics of the canonical theory, but their construction still suffers from ambiguities that render this correspondence only formal. To illustrate this, we first review the kinematical structure of loop quantum gravity. The SU(2) spin network states are given a new interpretation in terms of continuous geometries, which enables us to resolve an apparent tension between the geometrical interpretations underlying canonical loop quantum gravity and spin foams. After this interlude on the geometry of spin network states, we analyze the kinematical structure of the canonical theory outside of the time gauge, and discuss the choices of connection that are possible. We show in particular that the Lorentz-covariant extension of the usual Ashtekar- Barbero connection leads to a quantum theory that is equivalent to usual SU(2) loop quantum gravity, but that there exists an inequivalent quantization based on the so-called shifted connection. At the level of spin foam models, we present the influence of this choice of connection on the form of the constraints. We argue that the explicit imposition of the secondary second class constraints of the Plebanski theory is an essentiel ingredient in order to obtain the right quantum dynamics, and that the existing models are most likely not implementing this properly. A new three-dimensional model is introduced as a way to
Fairbairn, Winston J. "Inclusion de sources en théories de jauge quantiques invariantes sous difféomorphismes." Aix-Marseille 2, 2006. http://theses.univ-amu.fr.lama.univ-amu.fr/2006AIX22077.pdf.
We study the inclusion of matter sources in the quantum regime of certain background independent gauge theories. More precisely, we study the quantisation of general relativity casted as a dynamical theory of connections, and the quantisation of some topological theories of BF type. In the first part, where we develop the canonical quantisation program leading to loop quantum gravity, we present a solution to the separability problem of the kinematical Hilbert space and study the quantisation of the coupling of string-like sources to BF theory. In the second part, dedicated to the path integral quantisation, we present the most promising covariant or spinfoam models, construct a model of three dimensional quantum gravity coupled to fermionic fields and finally study the effects of the inclusion of a cosmological constant in the Lorentzian Barrett-Crane spinfoam model
Martin, Dussaud Pierre. "Black-to-white hole scenario : foundation and evaporation." Thesis, Aix-Marseille, 2020. http://www.theses.fr/2020AIXM0132.
The physics of the beginning of the 20th century experienced two major conceptual revolutions that changed the way we see the world. General relativity, on the one hand, describes space-time on a large scale; quantum mechanics, on the other hand, deals with the microscopic behaviour of matter. Since then, physicists have been looking for a theory of quantum gravity, which would bring the two languages together. It is expected that such a theory profoundly changes our understanding of black holes, these extremely dense astrophysical objects, long remained in the shade of calculations, and now observed in droves in the sky. Quantum theory has already shown, as a first approximation, that a black hole slowly evaporates. Quantum gravity also predicts that such an object could metamorphose into a white hole, its time-reverse. In this thesis, we study the foundations of such a scenario and propose a mathematical model that includes the phenomenon of evaporation
Poulain, Timothé. "On the quantum structure of spacetime and its relation to the quantum theory of fields : k-Poincaré invariant field theories and other examples." Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLS331/document.
As many theoretical studies point out, the classical description of spacetime, as a continuum, might be no longer adequate to reconcile gravity with quantum mechanics at very high energy (the relevant energy scale being often regarded as the Planck scale). Instead, a more appropriate description could be provided by the data of a noncommutative algebra of coordinate operators replacing the usual commutative local coordinates on smooth manifold. Once the noncommutative nature of spacetime is assumed, it is to expect that the (classical and quantum) properties of field theories on noncommutative background differ from the ones of field theories on classical background. This is the aim of Non-Commutative Field Theory (NCFT) to explore and study these new properties.In the present dissertation, we consider two families of quantum spacetimes of Lie algebra type noncommutativity. The first family is characterised by su(2) noncommutativity and appears in the description of some models of quantum gravity in 3-dimensions. The other family of quantum spacetimes is known in the physics literature as the 4-d kappa-Minkowski space. The importance of this quantum spacetime lies into the fact that its symmetries are provided by the (quantum) kappa-Poincaré algebra (a deformation of the classical Poincaré algebra) together with the fact that the deformation parameter 'kappa', which is of mass dimension, provides a natural energy scale at which the quantum gravity effects may be relevant (and is often regarded as being related to the Planck scale). For these reasons, the kappa-Minkowski space appears as a good candidate for a spacetime to be involved in the description of Doubly Special Relativity and Relative Locality models.To study NCFT it is often convenient to introduce a star product characterising the (noncommutative) C*-algebra of fields modelling the quantum spacetime under consideration. We emphasise that a canonical star product can be obtained by using the group algebraic structures underlying the construction of such Lie algebra type quantum spaces, namely by making use of harmonic analysis on the corresponding Lie group together with the Weyl quantisation scheme. The explicit derivation of such star product for kappa-Minkowski is given. In addition, we show that su(2) Lie algebras of coordinate operators related to quantum spaces with su(2) noncommutativity can be conveniently represented by SO(3)-equivariant poly-differential involutive representations and show that the quantized plane waves obtained from the quantization map action on the usual exponential functions are determined by polar decomposition of operators combined with constraint stemming from the Wigner theorem for SU(2). We finally indicate a convenient way to extend this construction to other semi-simple but non simply connected Lie groups by making use of results from group cohomology with value in an abelian group that would replace the constraints stemming from the simple Wigner theorem.Then, we investigate the quantum properties of various models of interacting scalar field theory on noncommutative background making use of the aforementioned star product formalism to construct physically reasonable expressions for the action functional. Considering quantum spacetime with su(2) noncommutativity, we find that the one-loop 2-point function for complex scalar field theories with quartic interactions is finite, the deformation parameter playing the role of a natural UV cut-off. Special attention is paid to the derivation of the one-loop corrections to both the 2-point and 4-point functions for various models of kappa-Poincaré invariant scalar field theory with quartic interactions. In that case, we show that for some models the 2-point function divergences linearly thus slightly milder than their commutative counterpart, while the one-loop 4-point function is shown to be finite. The results we obtained together with their consequences are finally discussed
Delepouve, Thibault. "Quartic Tensor Models." Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLS085/document.
Tensor models are probability measures for random tensors. They generalise matrix models and were developed to study random geometry in arbitrary dimension. Moreover, they are strongly connected to quantum gravity theories as, additionally to the standard bare-bones models, they encompass the field theoretical approach to loop quantum gravity known as group field theory.In the present thesis, we focus on the restricted case of quartic tensor models, for which a far greater number of rigorous mathematical results have been proven. Quartic models can be re-written as multi-matrix models using the intermediate field representation, and their perturbative expansions can be written as series expansions over combinatorial maps. Using a variety of map expansions, we prove analyticity results and useful bounds for the cumulants of various tensor models : the most general standard quartic model at any rank and the simplest renormalisable tensor field theory at rank 3. Then, we introduce a new class of models, the enhanced models, which perturbative expansions display new behaviour, different to the so called melonic behaviour that characterise most known tensor models so far
Liu, Hongguang. "Aspects of quantum gravity." Thesis, Aix-Marseille, 2019. http://www.theses.fr/2019AIXM0209.
This thesis mostly involves, but not restricts to, the problem of quantum gravity in the context of loop quantum gravity. Both fundamental aspects and the physical consequences of loop gravity are investigated in this work. We study the Lorentzian invariance of loop quantum gravity, in both the canonical approach and the spin foam model approach. We introduce an su(1, 1) gauge description of gravity theory in four dimensions, instead of the usual su(2) description. We investigate the loop quantization at the kinematical level, where we show that there is no anomaly between the su(1, 1) description and the su(2) description of space-like areas. Meanwhile, we perform the semi-classical (large-j asymptotic) analysis of the spin foam model (Conrady-Hnybida extension) in the most general situation, in which timelike tetrahedra with timelike triangles are taken into account. We identify the dominant contribution to the discrete simplicial geometries and recover the Regge action of gravity. On a second part of this thesis we focus on the problem of the high energy effective dynamics of loop gravity in cosmology and black holes through simplified models. We investigate the link between the family of extended Mimetic gravity, a class of scalar-tensor theories, and the effective dynamics of loop quantum cosmology as well as the spherical polymer black hole models inspired from loop quantum gravity. Futhermore, we solve the modified Einstein's equations explicitly in the framework of effective spherically symmetric polymer models. The effective metric for a static interior Black Hole geometry describing the trapped region is given
Ben, Achour Jibril. "Towards self dual Loop Quantum Gravity." Sorbonne Paris Cité, 2015. https://theses.hal.science/tel-01396791.
In this PhD thesis, we introduced a new strategy to investigate the kinematical and physical predictions of self dual Loop Quantum Gravity (LQG) and by-passed the old problem of implementing quantum mechanically the so called reality conditions inherent to the self dual formulation. This strategy relies on an analytic continuation which send the Barber() Immirzi parameter from its real value to the purely imaginary one, corresponding to the self dual variables. We investigate this procedure in the context of black holes quantization and show that it leads to a more satisfying derivation of the semi classical results of the thermodynamics of black hole within the LQG context. We investigate further this procedure in a toy model of three dimensional gravity, as well as in the context of Loop Quantum Cosmology. This procedure seems to provide an interesting candidate to investigate the self dual version of LQG, which has remain elusive since the very advent of the self dual variables in 1986
Livine, Etera R. "Boucles et mousses de spin en gravité quantique : une approche covariante à la quantification non-perturbative de la relativité générale." Aix-Marseille 2, 2003. http://www.theses.fr/2003AIX22022.
Sarno, Giorgio. "A numerical approach to spin foam models of quantum gravity." Thesis, Aix-Marseille, 2020. http://www.theses.fr/2020AIXM0231.
Spin foam models provide a Lorentz-covariant definition of the dynamics of loop quantum gravity. They offer a background-independent and non-perturbative quantization of gravity, and in their semiclassical limit, they are related to discretized General Relativity. However, the analytic complexity of the models is such that key questions concerning their theoretical consistency and physical predictions are still open. In this thesis, I introduce a systematic framework to perform numerical computations in this domain, to go beyond the limitations of the analytical techniques. The thesis contains an introduction to spin foam theories from a theoretical and a numerical standpoint, in particular to the EPRL model. I then present four of the six papers I published during my Ph.D., where the numerical framework was used to study critical open problems in the field. These include the numerical study of the semiclassical limit of a 4-simplex, recovering its Regge action and confirming known analytical computations ; a study of non-simplicial spin foams to offer an insight into the continuum limit of the theory ; a new approach to investigate extended triangulations and their semiclassical limit. Applied to a particular transition amplitude, the new approach allowed me to recover geometrical configurations compatible with curved boundary data, and to argue against an important dispute in the literature referred to as flatness problem. These results open a window for calculations in spin foam theories and they provide a new path to address their still unresolved questions
Grain, Julien. "Relativité générale et champs quantiques : quelques aspects de physique des trous noirs et de cosmologie en gravité de Lovelock, espaces de Sitter et dimensions supplémentaires." Université Joseph Fourier (Grenoble), 2006. http://www.theses.fr/2006GRE10153.
At the frontier of modern physics, the black hole evaporation process is undoubtedly the most favored phenomenon to get informations on quantum gravity. After a brief introduction to Einstien's General Relativity and to one of its extension as a Taylor expansion in scalar curvature, this thesis deals with the Hawking process focusing on the computation of greybody factors, i. E. The tunnel probablity for a particle, coming from the breaking of quantum vacuum fluctuations, to escape from the black hole's gravitational attraction. I have developped an analytical technique, based on semi-classical expansions, to study the dynamic of scalar fields propagating in static and spherically symmetric space-times as well as a numerical method to exactly compute those greybody factors for fields with an arbitrary spin. These methods are applied to the case of Schwarzschild black holes in the framework of the second order Lovelock gravity (Gauss-Bonnet gravity) with extra-dimensions, to get an exact determination of the radiation spectra, needed to check the principles of black hole's thermodynamics. Possible constrains on the gravitational Lagrangian using the black hole's evaporation process are also investigated in the framework of braneworld models a la Arkani-Hamed, Dimopoulos & Dvali (ADD), in which the Planck scale is around a TeV openning the possible production of black hole via the collsion of particles in the cosmos or at colliders: it is shown in this manuscript that the ADD scenarii are not in conflict with current data from cosmology and cosmic rays and that it will be possible, at the LHC, to distinguish between an Einstein-Hilbert Lagrangian with or without au Gauss-Bonnet term. The questions of primordial inhomogeneities and of dark matter are also explored in this thesis, respectively in the light of primordial black holes and extra-dimensional theories
Bourgine, Jean-Emile. "Modèles de matrices et problèmes de bord dans la gravité de Liouville." Phd thesis, Université Paris Sud - Paris XI, 2010. http://tel.archives-ouvertes.fr/tel-00541162.
Couturier, Camille. "Invariance de Lorentz et Gravité Quantique : contraintes avec des sources extragalactiques variables observées par H.E.S.S. et Fermi-LAT." Thesis, Paris 6, 2014. http://www.theses.fr/2014PA066555/document.
Some Quantum Gravity (QG) theories allow for a violation of Lorentz invariance (LIV), manifesting as a dependence on the velocity of light in vacuum on its energy. If such a dependence exists, then photons of different energies emitted together by a distant source will arrive at the Earth at different times. (Very) high energy transient emissions from distant astrophysical sources such as Gamma-ray Bursts (GRBs) and blazars can be used to search for and constrain LIV. This work presents the studies obtained with two leading Gamma-ray telescopes: H.E.S.S. -- for which a study of the quality of the calibrated data was performed -- and Fermi-LAT. The energies and arrival times of individual photons were used to constrain the vacuum dispersion parameter and the energy scale EQG at which QG effects causing LIV may arise. The maximum likelihood method is described, with detailed studies of the systematics. A modification for a non-negligible background is provided and applied to the data of an AGN flare observed by H.E.S.S.: the obtained limits on the QG energy scale are less constraining than the previous best limits obtained with blazars; yet, the new limits lie a redshift range not covered this far. Four bright and quasi background-free GRBs observed by the Fermi-LAT were also analysed, with two different template light curve determinations -- Gaussian fits and Kernel Density Estimates. The best limits on the E_QG scale for the linear/subluminal case are from the shortest burst, GRB090510: E_QG,1 > 7.6 E_Planck. More robust limits, considering the intrinsic effects possibly occurring at the source, were also derived
Ari, Wahyoedi Seramika. "La géométrie statistique : une étude sur les cases classique et quantique." Thesis, Aix-Marseille, 2016. http://www.theses.fr/2016AIXM4033.
A fixed theory of gravity is far from being complete. The most promising theory of gravity in this century is general relativity (GR), which is still plagued by several problems. The problems we highlight in this thesis are the thermodynamical aspects and the quantization of gravity. Attempts to understand the termodynamical aspect of GR have already been studied through the thermodynamics of black holes, while the theory of quantum gravity has already had several candidates, one of them being the canonical loop quantum gravity (LQG), which is the base theory in our work
Frodden, Ernesto. "Sur les propriétés thermodynamiques et quantiques des trous noirs." Thesis, Aix-Marseille, 2013. http://www.theses.fr/2013AIXM4059.
Black holes are studied from a theoretical point of view. The thermodynamics and quantum properties are addressed from a new perspective. A range of logically connected problems are explored: Starting from the laws of black hole mechanics, going through the Euclidean partition function, to the microscopic quantum granular models.The approach is supported by two guiding principles: What is physically relevant for black hole thermodynamics lays close to the horizon and the quantum geometry of the spacetime is coarse-grained.The first law of black hole mechanics is reviewed from the new quasilocal perspective based on near horizon observers. It turns out that the first law can be reformulated as variations of the area of the horizon. On the same grounds, the semiclassical Euclidean partition function is reviewed from the new quasilocal perspective. The framework reproduces the classic Bekenstein-Hawking entropy and the newly introduced quasilocal energy.The quasilocal approach can also be addressed by using Isolated Horizons. The quantization procedures are explored for the rotating Isolated Horizon starting from a symplectic structure analysis, and using the Loop Quantum Gravity Hilbert space. Finally, through a statistical analysis, the macroscopic consequences of the quantum granular model based on the Loop Quantum Gravity approach are studied. Special emphasis is put on the rotating quantum black hole model, however the results are not conclusive as several assumptions should be made on the way. Nevertheless, the perspective is promising as some of the semiclassical results, for instance the entropy, can be reproduced
Crépin, Pierre-Philippe. "Réflexion quantique d’un paquet d’onde d’antihydrogène refroidi." Thesis, Sorbonne université, 2019. http://www.theses.fr/2019SORUS054.
The framework of this thesis is the GBAR collaboration at CERN, which aims to measure the free fall acceleration of antimatter . In this thesis, we study the quantum reflection of the antihydrogen on the detector, caused by the Casimir-Polder interaction that we calculate for different materials. We find a particularly high quantum reflection for an antihydrogen atom on a surface of liquid helium. We then present a complete description of the gravitational quantum states, mixing gravity and Casimir-Polder interaction. For this purpose, we revisit the theory of collisions in the case of the Casimir-Polder potential through a new "effective range theory", obtained after a Liouville transform. The knowledge of gravitational quantum states leads us to propose a new method of measuring free fall acceleration, by creating quantum interferences between these states. A statistical analysis of the interference pattern thus obtained is carried out, leading to an improvement in the accuracy until three orders of magnitude compared to the initial free-fall experiment. Finally, we study in detail the influence of the disorder at the level of the plate of detection, the latter being in fact not a perfect surface. We calculate the effect of this disorder on the fluctuations of the Casimir-Polder potential itself, and observe a different behavior in law for the conductivity models such as the plasma model and the Drude model
Martineau, Killian. "Quelques aspects de cosmologie et de physique des trous noirs en gravitation quantique à boucles Detailed investigation of the duration of inflation in loop quantum cosmology for a Bianchi I universe with different inflaton potentials and initial conditions Some clarifications on the duration of inflation in loop quantum cosmology A first step towards the inflationary trans-Planckian problem treatment in loop quantum cosmology Scalar spectra of primordial perturbations in loop quantum cosmology Phenomenology of quantum reduced loop gravity in the isotropic cosmological sector Primordial Power Spectra from an Emergent Universe: Basic Results and Clarifications Fast radio bursts and the stochastic lifetime of black holes in quantum gravity Quantum fields in the background spacetime of a polymeric loop black hole Quasinormal modes of black holes in a toy-model for cumulative quantum gravity Seeing through the cosmological bounce: Footprints of the contracting phase and luminosity distance in bouncing models Dark matter as Planck relics without too exotic hypotheses A Status Report on the Phenomenology of Black Holes in Loop Quantum Gravity: Evaporation, Tunneling to White Holes, Dark Matter and Gravitational Waves." Thesis, Université Grenoble Alpes (ComUE), 2019. http://www.theses.fr/2019GREAY044.
After decades of being confined to mathematical physics, quantum gravity now enters the field of experimental science. Following this trend, we consider throughout this thesis three implementation frameworks of Loop Quantum Gravity (LQG): the Universe as a system, black holes and astroparticles. The last one is only outlined while the first two are presented in more detail.Since the cosmological sector is one of the most promising areas for testing and constraining quantum gravity theories, it was not long before the development of different models attempting to apply the ideas of the LQG to the primordial Universe. The work we present deals with the phenomenology associated with these models; both in the homogeneous sector (where we focus particularly on the duration of the inflation phase), as in the inhomogeneous sector (where this time, we study the fate of the primordial power spectra). These combined studies then allow us to specify to what extent effects of (loop) quantum gravity can be observed in the anisotropies of the cosmic microwave background.On the other hand black holes, not content to be among the strangest and most fascinating objects of the Universe, are also prominent probes to test the theories of gravitation. We develop the phenomenology associated with different treatments of black holes in the loop quantum gravity framework, which intervenes on multiple levels: from the evaporation of Hawking to gravitational waves, including dark matter. This is undoubtedly a rich and vast area.Finally, the existence of a minimal length scale, predicted by the majority of quantum gravity theories, suggests a generalization of the Heisenberg uncertainty principle. On the basis of this observation, we also present in this manuscript a methodology to derive a new relation dispersion of light from the most widely used generalized uncertainty principle
Bautista, Solans Maria Teresa. "Weyl anomalies and quantum cosmology." Thesis, Paris 6, 2016. http://www.theses.fr/2016PA066329/document.
In this thesis we study the cosmological consequences of Weyl anomalies arising from the renormalization of composite operators of the fundamental fields, including the metric. These anomalies are encoded in the gravitational dressings of the operators in a non-local quantum effective action. We derive the evolution equations that follow from this action and look for cosmological solutions. For simplicity, we focus on Einstein-Hilbert gravity with a cosmological constant. We first consider two-dimensional gravity, where Liouville theory allows us to compute the gravitational dressing of the cosmological constant operator. Using a Weyl-invariant formulation, we determine the gauge-invariant but non-local effective action, and compute the corresponding non-local momentum tensor. The Weyl anomalies modify the full quantum momentum tensor, not only its trace, and hence lead to interesting effects in the cosmological dynamics. In particular, we find a decaying vacuum energy and a slow-down of the de Sitter expansion. In four dimensions, motivated by our results in two dimensions, we parametrize the effective action with scale-dependent gravitational dressings, and compute the general evolution equations. In the approximation of constant anomalous dimensions, the momentum tensor leads to a decaying vacuum energy and a slow-roll quasi-de Sitter expansion, just as in two dimensions. The anomalous dimensions are in principle computable in a given microscopic theory using semiclassical methods. Even though the anomalous dimensions are small in perturbation theory, their integrated effect over several e-folds could add up to something significant during primordial cosmology
Ponsot, Bénédicte. "Théorie de Liouville et un groupe quantique non compact." Montpellier 2, 2000. http://www.theses.fr/2000MON20045.
Harada, Masaki (1967 ). "La physique au carrefour de l'intuitif et du symbolique : une étude épistémologique des concepts quantiques à la lumière de la phénoménologie herméneutique." Paris 7, 2005. http://www.theses.fr/2005PA070004.
P. Ricœur establishes a relationship between epistemology and hermeneutical phenomenology, in considering epistemology as mediation between phenomenology and hermeneutics. This dissertation demonstrates that even if Ricœur's philosophy does not refer to the epistemology of natural sciences, the latter can be deepened by hermeneutical phenomenology. Quantum theory is analysed in order to reveal a spiral movement in the construction of this physical theory, which can be considered as a hermeneutical circle. Quantum theory is often considered as symbolic rather than intuitive. However, we regard the intuitive as reconstructed through the symbolic. Quantum theory concepts are located at the conjuncture of the intuitive and the symbolic. To demonstrate this, an analysis is made of the relationship between geometries and algebras, of the relationship between the concept of particle and the concept of wave, and of the reconstruction of the concept of locality within quantum theory. For this purpose, an epistemology that is open to hermeneutical phenomenology is employed
Carrozza, Sylvain. "Methodes tensorielles et renormalization appliquées aux théories GFT." Phd thesis, Université Paris Sud - Paris XI, 2013. http://tel.archives-ouvertes.fr/tel-00872784.
Feller, Alexandre. "Entanglement and Decoherence in Loop Quantum Gravity." Thesis, Lyon, 2017. http://www.theses.fr/2017LYSEN058/document.
A quantum theory of gravitation aims at describing the gravitational interaction at every scales of energy and distance. However, understanding the emergence of our classical spacetime is still an open issue in many proposals. This thesis analyzes this problem in loop quantum gravity with tools borrowed from quantum information theory.This is done in several steps. Since loop quantum gravity is still under construction, a pragmatic point of view is advocated and an ansazt for physical states of the gravitational field is studied at first, motivated from condensed matter physics and simple intuitions. We analyze the proposal of reconstructing geometry from correlations. Lessons on the quantum dynamics and the Hamiltonian constraint are extracted. The second aspect of this work focuses on the physics of sub-systems and especially the physics of their boundary. We begin by calculating the entanglement entropy between the interior and the exterior of the region, recovering the holographic law known from classical black hole physics. Then different boundary dynamics are studied, both in the isolated and open cases, which shed lights again on the fundamental dynamics. Finally, the last aspect of this research studies the dynamics of the boundary interacting with an environment whose degrees of freedom (gravitational or matter) forming the rest of the Universe and especially the decoherence it induces. This allows to discuss the quantum to classical transition and understand, in a given model, the pointer states of geometry
Laidet, Julien. "Collisions à Haute Energie de Hadrons Denses en Chromodynamique Quantique : Phénoménologie du LHC et Universalité des Distributions de Partons." Phd thesis, Ecole Polytechnique X, 2013. http://pastel.archives-ouvertes.fr/pastel-00875951.
Riello, Aldo. "Corrections radiatives en gravité quantique à mousse de spins : Une étude du graphe de Self énergie dans le modèle EPRL Lorentzien." Thesis, Aix-Marseille, 2014. http://www.theses.fr/2014AIXM4028/document.
I present the first quantitative study of radiative corrections within the EPRL model of quantum gravity. This model is the most advanced proposal of Lorentzian 4-dimensional background-independent quantum gravity. It is a realization of the path-integral quantization of general relativity as a sum over geometries. The present study focuses on the properties and geometrical features of the analogue of the self-energy graph within the model, often referred to as the "melon"-graph. Here, I show that the dominating contribution to such a graph is characterized by a degree of divergence much smaller than that of closely related topological quantum field theories. Moreover, I work out in detail the dependence of the amplitude from the boundary data, and find that the self-energy graph does not simply induce a wave function renormaliziation. This happens for reasons deeply related to the model foundations. However, it turns out that the amplitude reduces to a wave function renormalzation in the limit of large quantum numbers. Then, I show the consequences of this calculations on a concrete spinfoam observable: the quantum-metric two-point function. In doing this, I show how the insertion of the self-energy graph in the bulk of the (first-order) spinfoam used in the calculation, has non-trivial effects on the correlation function, modifying its leading order contributions. Most interestingly, this effects do not disappear in the limit of large quantum number. Finally, I discuss the consequences of these calculations for the model itself, and I point out and comment those general features which seem to be common to any spinfoam model based on the present model-building schemes
Bonzom, Valentin. "Géométrie quantique dans les mousses de Spins : de la théorie topologique BF vers la relativité générale." Thesis, Aix-Marseille 2, 2010. http://www.theses.fr/2010AIX22072/document.
Loop quantum gravity has provided us with a canonical framework especially devised for back-ground independent and diffeomorphism invariant gauge field theories. In this quantization the funda-mental excitations are called spin network states, and in the context of general relativity, they give ameaning to quantum geometry. Spin foams are a sort of path integral for spin network states, supposed to enable the computations of transition amplitudes between these states. The spin foam quantization has proved very efficient for topological field theories, like 2d Yang-Mills, 3d gravity or BF theories. Different models have also been proposed for 4-dimensional quantum gravity.In this PhD manuscript, I discuss several methods to study spin foam models. In particular, I present some recurrence relations on spin foam amplitudes, which generically encode classical symme-tries at the quantum level, and are likely to help fill the gap with the Hamiltonian constraints. These relations can be naturally interpreted in terms of elementary deformations of discrete geometric struc-tures, like simplicial geometries. Another interesting method consists in exploring the way spin foam models can be written as path integrals for systems of geometries on a lattice, taking inspiration from topological models and Regge calculus. This leads to a very geometric view on spin foams, and gives classical action principles which are studied in details
Tilloy, Antoine. "Mesure continue en mécanique quantique : quelques résultats et applications." Thesis, Paris Sciences et Lettres (ComUE), 2016. http://www.theses.fr/2016PSLEE010/document.
This thesis is devoted to the study of the quantum trajectories obtained from thetheory of continuous measurement in non relativistic quantum mechanics. New theoretical resultsas well as examples of applications are presented. On the theoretical front, we study mostly thelimit of «strong» measurement where we put forward the emergence of quantum jumps and quantumspikes, two phenomena we characterize in detail. Out of the strong measurement limit, weinvestigate a method to extract information from a register of qubits optimally. On the applicationfront, we introduce an original method to control quantum systems exploiting only the freedomof changing the measurement intensity and we explain the transition between a ballistic and adiffusive behavior in open quantum random walks; two byproduct of the theoretical study of thestrong measurement regime. We further study the problem of semi-classical gravity and show thatcontinuous measurement theory allows to construct a consistent model in the Newtonian regime.We eventually suggest possible extensions of the formalism to a posteriori estimation and hint atgeneralizations of the results for the strong measurement limit in the wider context of discreterepeated measurements. In the course of our presentation, we emphasize the link with other approachesto the theory of continuous measurement (parallels with stochastic filtering and collapsemodels in foundations) rather than aim for mathematical rigor