Academic literature on the topic 'Quantum space-times'
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Journal articles on the topic "Quantum space-times":
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Calmet, Xavier, Roberto Casadio, and Folkert Kuipers. "Singularities in quantum corrected space-times." Physics Letters B 807 (August 2020): 135605. http://dx.doi.org/10.1016/j.physletb.2020.135605.
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Davis, Simon. "Desingularization of Black Hole Space-Times." Bulletin of Pure and Applied Sciences – Physics 42, no. 1 (June 17, 2023): 6–34. http://dx.doi.org/10.48165/bpas.2023.42d.1.2.
Abstract:
The desingularization of a class of black hole space-times arising as solutions to the string equations is considered in connection with the consistency of the quantum theory and the description of nonperturbative states with quantum numbers from the particle spectrum. The geometry arising in an extreme limit of one of the singular solutions to the gravitational field equations is demonstrated to be a background of N = 2 string theory. The positivity of the masses in the particle spectrum is proven through quasilocal integrals near the resolved singularities in these limits of black hole space-times.
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KONKOWSKI, D. A., and T. M. HELLIWELL. "QUANTUM SINGULARITIES IN STATIC AND CONFORMALLY STATIC SPACE-TIMES." International Journal of Modern Physics A 26, no. 22 (September 10, 2011): 3878–88. http://dx.doi.org/10.1142/s0217751x11054334.
Abstract:
The definition of quantum singularity is extended from static space-times to conformally static space-times. After the usual definitions of classical and quantum singularities are reviewed, examples of quantum singularities in static space-times are given. These include asymptotically power-law space-times, space-times with diverging higher-order differential invariants, and a space-time with a 2-sphere singularity. The theory behind quantum singularities in conformally static space-times is followed by an example, a Friedmann-Robertson-Walker space-time with cosmic string. The paper concludes by discussing areas of future research.
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KONKOWSKI, D. A., and T. M. HELLIWELL. "QUANTUM SINGULARITIES IN STATIC AND CONFORMALLY STATIC SPACE-TIMES." International Journal of Modern Physics: Conference Series 03 (January 2011): 364–74. http://dx.doi.org/10.1142/s2010194511001462.
Abstract:
The definition of quantum singularity is extended from static space-times to conformally static space-times. After the usual definitions of classical and quantum singularities are reviewed, examples of quantum singularities in static space-times are given. These include asymptotically power-law space-times, space-times with diverging higher-order differential invariants, and a space-time with a 2-sphere singularity. The theory behind quantum singularities in conformally static space-times is followed by an example, a Friedmann-Robertson-Walker space-time with cosmic string. The paper concludes by discussing areas of future research.
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Parmeggiani, Claudio. "Quantum fields and gravity: Expanding space-times." International Journal of Modern Physics A 35, no. 02n03 (January 30, 2020): 2040039. http://dx.doi.org/10.1142/s0217751x20400394.
Abstract:
We discuss a proposal for a somewhat new formulation of quantum field theory (set in a four-dimensional manifold, the space-time) that includes an analysis of its implications for the evolution of Einstein-Friedmann cosmological models. The proposed theory displays two peculiar features: (i) a local Hilbert-Fock space is associated with each space-time point: we are dealing with a vector bundle whose fibers are Hilbert spaces; the operator-valued sections of the bundle are the quantum fields; (ii) the vacuum energy density is finite, being regularized in a space-time curvature dependent way, independently at each point. In fact everything is finite: self-masses, self-charges, quantum fluctuations: they depend on the space-time curvature and diverge only for a flat metric. In an Einstein-Friedmann model the vacuum (zero-point) energy density is consequently time-dependent and in general not negligible. Then it is shown that, for some choices of the parameters of the theory, the big-bang singularity is resolved and replaced by a bounce driven by the vacuum energy density, which becomes (very) large and negative near the bounce (negative by the contribution of the Fermi fields). But for large times (now, say) the Bose fields’ positive vacuum energy eventually overcomes the negative one and we are finally left with the present vacuum energy: positive and reasonably small.
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Hudson, R. L. "Stop times in Fock space quantum probability." Stochastics 79, no. 3-4 (June 2007): 383–91. http://dx.doi.org/10.1080/17442500601078966.
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Balachandran, AP. "Quantum space-times in the year 2002." Pramana 59, no. 2 (August 2002): 359–68. http://dx.doi.org/10.1007/s12043-002-0128-y.
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Sánchez, N. "Quantum string theory in curved space-times." Astronomische Nachrichten: A Journal on all Fields of Astronomy 311, no. 4 (1990): 231–38. http://dx.doi.org/10.1002/asna.2113110408.
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Janssen, Daan W. "Quantum Fields on Semi-globally Hyperbolic Space–Times." Communications in Mathematical Physics 391, no. 2 (February 21, 2022): 669–705. http://dx.doi.org/10.1007/s00220-022-04328-7.
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AbstractWe introduce a class of space–times modeling singular events such as evaporating black holes and topology changes, which we dub as semi-globally hyperbolic space–times. On these space–times we aim to study the existence of reasonable quantum field theories. We establish a notion of linear scalar quantum field theories on these space–times, show how such a theory might be constructed and introduce notions of global dynamics on these theories. Applying these contructions to both black hole evaporation and topology changing space–times, we find that existence of algebras can be relatively easily established, while the existence of reasonable states on these algebras remains an unsolved problem.
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SKÁKALA, JOZEF, and MATT VISSER. "PSEUDO-FINSLERIAN SPACE–TIMES AND MULTIREFRINGENCE." International Journal of Modern Physics D 19, no. 07 (July 2010): 1119–46. http://dx.doi.org/10.1142/s0218271810017172.
Abstract:
Ongoing searches for a quantum theory of gravity have repeatedly led to the suggestion that space–time might ultimately be anisotropic (Finsler-like) and/or exhibit multirefringence (multiple signal cones). Multiple (and even anisotropic) signal cones can be easily dealt with in a unified manner, by writing down a single Fresnel equation to simultaneously encode all signal cones in an even-handed manner. Once one gets off the signal cone and attempts to construct a full multirefringent space–time metric the situation becomes more problematic. In the multirefringent case we shall report a significant no-go result: in multirefringent models there is no simple or compelling way to construct any unifying notion of pseudo-Finsler space–time metric, different from a monorefringenent model, where the signal cone structure plus a conformal factor completely specifies the full pseudo-Riemannian metric. To throw some light on this situation we use an analog model where both anisotropy and multirefringence occur simultaneously: biaxial birefringent crystal. But the significance of our results extends beyond the optical framework in which (purely for pedagogical reasons) we are working, and has implications for any attempt at introducing multirefringence and intrinsic anisotropies to any model of quantum gravity that has a low energy manifold-like limit.
Dissertations / Theses on the topic "Quantum space-times":
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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.
Abstract:
La géométrie noncommutative est un formalisme mathématique qui exprime la structure de l’espace-temps avec des algèbres d’opérateurs. On s’attend à ce que les espace-temps noncommutatifs fassent émerger des effets de gravité quantiques, au moins dans un certain régime, notamment parce qu’ils utilisent les outils de la mécanique quantique pour décrire la géométrie. Ce manuscrit se concentre sur les aspects physiques de ces espace-temps quantiques, tout particulièrement à travers le formalisme des théories de champs et de jauge. Il est montré que les théories de champs scalaires engendrent possiblement des divergences dans l’infra-rouge et l’ultra-violet pour la fonction 2-point à une boucle. Ce phénomène s’appelle génériquement le mélange UV/IR et découle de la divergence du propagateur. L’analyse de ces divergences diffèrent du cas commutatif car l’espace des moments y est noncommutatif. D’autre part, une théorie de jauge sur κ-Minkowski, une déformation quantique de l’espace de Minkowski, est construite. Un premier calcul perturbatif produit une brisure de l’invariance de jauge, un comportement pathologique commun à d’autres espace-temps quantiques. Un modèle-jouet de causalité est aussi développé sur κ-Minkowski, dans lequel apparaît un analogue de la vitesse de lumière comme vitesse limite. La phénoménologie de la gravité quantique émergeant des espace-temps quantiques est abordée, avec les contraintes qu’elle impose. Finalement, un modèle-jouet de gravité noncommutative, utilisant κ-Minkowski pour décrire l’espace tangent, est traité. Il nécessite le concept de partition de l’unité noncommutative spécialement défini dans ce contexteNoncommutative 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
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Dang, Nguyen Viet. "Renormalization of quantum field theory on curved space-times, a causal approach." Paris 7, 2013. http://www.theses.fr/2013PA077188.
Abstract:
Le sujet de la thèse est la construction d'une théorie perturbative des champs quantiques en interaction sur un espace-temps courbe, suivant un point de vue conçu par Stueckelberg et Bogoliubov et developpé par Epstein-Glaser sur l'espace de Minkowski plat. En 2000 un progrès important fut réalisé par Brunetti et Fredenhagen qui réussirent à étendre la théorie d'Epstein-Glaser en exploitant le point de vue développé par Radzikowski pour definir les états quantiques sur un espace-temps courbe en terme d'ensembles de front d'onde. Ces résultats furent ultérieurement généralisés par Fredenhagen, Brunetti, Hollands, Wald, Rejzner, etc. Aux théories de Yang-Mills et de la gravitation. Cependant, même pour des théories sans invariance de jauge, de nombreux détails mathématiques sont restés inexplorés et parfois sans vérification. Dans cette thèse, on construit d'une façon totalement rigoureuse cette théorie dans le cas des champs sans invariance de jauge. Dans mon travail, j' ai revisité complètement cette théorie, résolvant au passage plusieurs questions laissées en suspens, incorporant de nombreux résultats nouveaux autour de ce programme et, le cas échéant, apportant des détails beaucoup plus précis sur les contre-termes dans le processus de renormalisation, une compréhension plus approfondie des ambiguïtés et une description géométrique des ensembles de front d'onde. L'ensemble de la thèse utilise un large éventail de techniques mathématiques : de la géométrie différentielle et pseudo riemannienne, des techniques d'analyse micro-locale et de géométrie symplectique pour les fronts d'onde, de l'analyse fonctionnelle, des résultats fins de la théorie des distributionsThe 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
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Cozzella, Gabriel [UNESP]. "Information loss in black holes and the unitarity of quantum mechanics." Universidade Estadual Paulista (UNESP), 2016. http://hdl.handle.net/11449/143416.
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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
A teoria quântica de campos em espaços-tempos curvos é o arcabouço teórico mais sólido que temos para estudar a interação entre gravitação e mecânica quântica na ausência de uma teoria completa de gravitação quântica. Neste contexto, um problema que atraiu muita atenção dos físicos teóricos nas últimas décadas é o chamado “paradoxo da perda de informação em buracos negros”, onde a evolução de um estado quântico puro inicial para um estado quântico misto final caracterizaria uma violação das leis da mecânica quântica. Nesta dissertação nós argumentamos que a perda de informação em si não viola as leis da mecânica quântica e é consequência direta da teoria semi-clássica utilizada. Finalmente, argumentamos que a questão da recuperação da informação deve ser tratada utilizando-se uma teoria de gravitação quântica ainda desconhecida.
The quantum theory of fields in curved space-times is the most solid framework for studying the interplay between gravity and quantum mechanics in the absence of a complete theory of quantum gravity. In this scenario, one problem that has drawn much attention from the theoretical physics community in the last decades is the so-called “black hole information loss paradox”, where the evolution from an initial pure quantum state to a final mixed quantum state would constitute a violation of the laws of quantum mechanics. In this dissertation we argue that information loss does not violate quantum mechanics, being simply a consequence of the semi-classical framework adopted and that the question of information recovery needs to be addressed by a yet unknown theory of quantum gravity.
FAPESP: 2014/08684-9
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Cavalcante, Everton. "Aspectos geométricos da molécula de fulereno em referenciais não-inerciais." Universidade Federal da Paraíba, 2015. http://tede.biblioteca.ufpb.br:8080/handle/tede/9557.
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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES
In this thesis we study the dynamics of charge carriers, and the electronic properties, of the C60 fullerene molecule. Characterizing it by a geometric bias. In inertial reference systems and when we have your material under rotation content. Initially we discussed the scientific advent of carbon allotropes, and the importance of modelling its derivates at low energies. We show that at low energies, the graphene - the two-dimensional carbon allotrope form - can be described for a non-massive theory of free fermions. At a second moment, we extended the nonmassive free fermions theory for the C60 molecule. Assuming the hexagonal graphene network can be entered in fullerene when we introduce topological defects. A brief study of topological defects in condensed matter was done. And soon after, we made a description these defects via a non-Euclidean geometry. Showing how the charge carriers in the network see the defects like gauge fields. Then we began to expose the results of this thesis. First we assume the fullerene by a two-dimensional spherical metric with defects, containing a fictitious t’Hooft-Polyakov monopole in its center. TheC60 is still subjected to the action of an Aharonov-Bohm flux arising of a magnetic wire running through its poles. So we get the spectrum, and the prediction of a persistent current in the molecule. Finally we return to the analysis of the molecule, now with your content of matter under rotation. For this, we studied a metric Gödel-type with spherical symmetry. We discussed the problem of causality and obtain the spectrum and the persistent current in terms of the vorticity (W) of spacetime.
Nesta tese estudamos a dinâmica de portadores de carga, e as propriedades eletrônicas, na molécula de fulerenoC60. Caracterizando-a por um viés geométrico. Tanto em sistemas de referência inercial, como quando temos seu conteúdo de matéria sob rotação. Inicialmente abordamos o advento científico das formas alotrópicas do carbono e a importância da modelagem a baixas energias dos seus derivados. Onde mostramos que no limite de baixas energias, o grafeno - que trata-se da forma alótropica bidimensional do carbono - pode ser descrito por uma teoria de férmions livres sem massa. Num segundo momento estendemos a teoria de férmions não massivos para a molécula de C60. Assumindo que a rede hexagonal do grafeno pode inscrever o C60 ao introduzirmos alguns defeitos topológicos. Um breve estudo sobre os defeitos topológicos na matéria condensada foi feito. Onde, logo em seguida, partimos para uma descrição de tais defeitos via uma geometria não-euclidiana. Mostrando como os portadores de carga no meio enxergam os defeitos como campos de gauge. Em seguida começamos a expor os resultados desta tese. Primeiramente assumimos tratar o fulereno por uma métrica de uma esfera bidimensional com defeitos, e contendo um monopolo de t’Hooft-Polyakov fictício em seu centro. O C60 é ainda submetido a ação de um fluxo de Aharonov-Bohm advindo de uma corda magnética quiral transpassando seus polos. Obtemos assim o espectro e a predição de uma corrente persistente na molécula. Por fim retomamos a análise da molécula, agora com seu conteúdo de matéria sob rotação. Para isso assumimos tratar o fulereno por uma métrica do tipo Gödel com simetria esférica. Discutimos o problema da causalidade e obtemos espectro e corrente persistente em termos da vorticidade (W) do espaço-tempo.
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Dawson, Simon P. "Bounds on negative energy densities in quanum field theories on flat and curved space-times." Thesis, University of York, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.437627.
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Pereira, Dante Donizeti. "Abordagem efetiva em teorias de campos: aspectos clássicos e quânticos." Universidade Federal de Juiz de Fora (UFJF), 2013. https://repositorio.ufjf.br/jspui/handle/ufjf/4892.
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CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
Nesta tese exploramos diferentes aspectos de teorias clássicas e quânticas de campos. Na parte clássica, examinamos o fenômeno da birrefringência eletro-magneto-óptica em ele-trodinâmica não-linear no contexto de meios materiais dielétricos não-lineares como uma correção efetiva à teoria linear maxwelliana do eletromagnetismo. Na parte quântica, seguindo o método do heat kernel em teoria quântica de campos sobre espaços curvos, derivamos e estudamos a estrutura das divergências a 1-loop para a ação efetiva de diferentes modelos. Em particular, no ramo do modelo de Yukawa, exibimos duas novas formas de ambiguidades as quais tomam lugar na ação efetiva de campos fermiônicos através do fenômeno da anomalia multiplicativa não-local. Além disso, analisamos a estrutura das divergências ultravioletas a 1-loop para um modelo recentemente proposto de gravitação massiva livre de fantasmas, e mostramos que esse modelo encontra sérias dificuldades no nível quântico.
In this thesis we explore different aspects in classical and quantum field theories. In the classical part, we examine the phenomenon of electro-magneto-optical birefringence in nonlinear electrodynamics in the context of nonlinear dielectric media as an effective correction to the linear Maxwellian theory of electromagnetism. In the quantum part, following the heat kernel method in quantum field theory on curved spaces, we derive and study the structure of the 1-loop divergences for the effective action of different models. In particular, through the Yukawa model, we show two new forms of ambiguities which take place in the effective action of fermionic fields through the phenomenon of nonlocal multiplicative anomaly. Moreover, we analyzed the structure of ultraviolet divergences at 1-loop for a recently proposed ghost-free massive gravity model, and we show that this model meets serious difficulties at the quantum level.
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Taslimitehrani, Mojtaba. "Aspects of Gauge Theories in Lorentzian Curved Space-times." 2018. https://ul.qucosa.de/id/qucosa%3A32454.
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We study different aspects of perturbatively renormalized quantum gauge theories in the presence of non-trivial background Lorentzian metrics and background connections. First, we show that the proof of nilpotency of the renormalized interacting BRST charge can be reduced to the cohomological analysis of the classical BRST differential. This result guarantees the self-consistency of a class of local, renormalizable field theories with vanishing 'gauge anomaly'' at the quantum level, such as the pure Yang-Mills theory in four dimensions. Self-consistency here means that the algebra of gauge invariant observables can be constructed as the cohomology of this charge.
Second, we give a proof of background independence of the Yang-Mills theory. We define background independent observables in a geometrical formulation as flat sections of a cohomology algebra bundle over the manifold of background configurations, with respect to a flat connection which implements background variations. We observe that background independence at the quantum level is potentially violated. We, however, show that the potential obstructions can be removed by a finite renormalization.
Third, we construct the advanced/retarded Green's functions and Hadamard parametrices for linearized Yang-Mills and Einstein equations in general linear covariant gauges. They play an essential role in formulating gauge theories in curved spacetimes.
Finally, we study a superconformal gauge theory in three dimensions (the ABJM theory) which is conformally coupled to a curved background. The superconformal symmetry of this theory is described by a conformal symmetry superalgebra on manifolds which admit twistor spinors.
By analyzing the relevant cohomology class of an appropriate BV-BRST differential, we show that the full superalgebra is realized at the quantum level.
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Kozoň, Marek. "Semiklasická energie eliptické Nambuovy-Gotovy struny." Master's thesis, 2018. http://www.nusl.cz/ntk/nusl-392428.
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Po zhrnutí potrebných teoretických základov a predošlého výskumu v ob- lasti, prezentujeme semi-klasickú kvantovaciu schému pre uzavretú Nambuovu- Gotovu strunu. Týmto zovšeobecňujeme predošlú prácu, ktorá bola vykonaná pre otvorenú strunu a uzavretú strunu kruhového tvaru. Pomocou metód kvan- tovej teórie po©a v zakrivených priestoročasoch počítame strednú hodnotu vo©- ného Hamiltoniánu struny rotujúcej v dvoch na seba kolmých priestorových rovinách v priestoročase všeobecnej dimenzie. Táto hodnota je priamo úmerná kvantovej korekcii k celkovej energii struny, ktorá má formu tzv. Reggeovho interceptu. Výslednú hodnotu Reggeovho interceptu porovnávame s predošlým výskumom. Taktiež uvádzame porovnanie získaného spektra fyzikálnych stavov struny kvantovanej našou metódou so spektrom odvodeným pomocou kovariant- ného kvantovania. 1
Books on the topic "Quantum space-times":
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Ottaviani, Jim. Feynman. New York: First Second, 2011.
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Hawking, S. W. The illustrated A brief history of time. New York: Bantam Books, 1996.
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Hawking, S. W. A brief history of time: From the big bang to black holes. Toronto: Bantam Books, 1988.
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Hawking, S. W. A brief history of time: From the big bang to black holes. Oxford: ISIS Large Print, 1989.
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Hawking, S. W. Shi jian jian shi: Cha tu ban. 8th ed. Changsha Shi: Hunan ke xue ji shu chu ban she, 2007.
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Hawking, S. W. A brief history of time. New York: Bantam Books, 1998.
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Hawking, S. W. A brief history of time: From the big bang to black holes. New York: Bantam Books, 1989.
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Hawking, S. W. Kratka︠i︡a istori︠i︡a vremeni: Ot bolʹshogo vzryva do chernykh dyr. Sankt-Peterburg: Amfora, 2009.
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Hawking, S. W. Dal Big Bang ai buchi neri. Milano: Rizzoli, 2000.
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Hawking, S. W. A Brief History of Time: From the Big Bang to Black Holes. London, UK: Bantam Books Ltd, 1995.
Book chapters on the topic "Quantum space-times":
1
Ashtekar, Abhay. "Quantum Space-Times." In Minkowski Spacetime: A Hundred Years Later, 163–96. Dordrecht: Springer Netherlands, 2009. http://dx.doi.org/10.1007/978-90-481-3475-5_7.
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Sanchez, N. "Quantum Strings in Curved Space Times." In NATO ASI Series, 265–315. Boston, MA: Springer US, 1990. http://dx.doi.org/10.1007/978-1-4615-3814-1_10.
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Ribeiro, Pedro Lauridsen. "Algebraic Holography in Asymptotically Simple, Asymptotically AdS Space-times." In Rigorous Quantum Field Theory, 253–70. Basel: Birkhäuser Basel, 2007. http://dx.doi.org/10.1007/978-3-7643-7434-1_18.
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Rumpf, Helmut. "Quantum Field Theory in Non-globally Hyperbolic Space-Times." In Geometry and Quantum Physics, 400. Berlin, Heidelberg: Springer Berlin Heidelberg, 2000. http://dx.doi.org/10.1007/3-540-46552-9_24.
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Sánchez, Norma. "Field and String Quantization in Curved Space-Times." In Quantum Mechanics of Fundamental Systems 2, 203–29. Boston, MA: Springer US, 1989. http://dx.doi.org/10.1007/978-1-4613-0797-6_13.
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Audretsch, Jürgen. "Mutually interacting quantum fields in curved space-times." In Field Theory, Quantum Gravity and Strings II, 68–81. Berlin, Heidelberg: Springer Berlin Heidelberg, 1987. http://dx.doi.org/10.1007/3-540-17925-9_30.
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Williams, Floyd. "Helmholtz Free Energy for Certain Negatively Curved Space-Times, and the Selberg Trace Formula." In Topics in Quantum Mechanics, 321–32. Boston, MA: Birkhäuser Boston, 2003. http://dx.doi.org/10.1007/978-1-4612-0009-3_17.
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Audretsch, Jürgen. "Mutually Interacting Quantum Fields in Curved Space-Times: The Outcome of Physical Processes." In NATO ASI Series, 233–64. Boston, MA: Springer US, 1990. http://dx.doi.org/10.1007/978-1-4615-3814-1_9.
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Galimberti, Andrea. "FPGA-Based Design and Implementation of a Code-Based Post-quantum KEM." In Special Topics in Information Technology, 27–40. Cham: Springer Nature Switzerland, 2024. http://dx.doi.org/10.1007/978-3-031-51500-2_3.
Abstract:
AbstractPost-quantum cryptography aims to design cryptosystems that can be deployed on traditional computers and resist attacks from quantum computers, which are widely expected to break the currently deployed public-key cryptography solutions in the upcoming decades. Providing effective hardware support is crucial to ensuring a wide adoption of post-quantum cryptography solutions, and it is one of the requirements set by the USA’s National Institute of Standards and Technology within its ongoing standardization process. This research delivers a configurable FPGA-based hardware architecture to support BIKE, a post-quantum QC-MDPC code-based key encapsulation mechanism. The proposed architecture is configurable through a set of architectural and code parameters, which make it efficient, providing good performance while using the resources available on FPGAs effectively, flexible, allowing to support different large QC-MDPC codes defined by the designers of the cryptosystem, and scalable, targeting the whole Xilinx Artix-7 FPGA family. Two separate modules target the cryptographic functionality of the client and server nodes of the quantum-resistant key exchange, respectively, and a complexity-based heuristic that leverages the knowledge of the time and space complexity of the configurable hardware components steers the design space exploration to identify their best parameterization. The proposed architecture outperforms the state-of-the-art reference software that exploits the Intel AVX2 extension and runs on a desktop-class CPU by 1.77 and 1.98 times, respectively, for AES-128- and AES-192-equivalent security instances of BIKE, and it provides a speedup of more than six times compared to the fastest reference state-of-the-art hardware architecture, which targets the same FPGA family.
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Guan, Ji, Wang Fang, and Mingsheng Ying. "Verifying Fairness in Quantum Machine Learning." In Computer Aided Verification, 408–29. Cham: Springer International Publishing, 2022. http://dx.doi.org/10.1007/978-3-031-13188-2_20.
Abstract:
AbstractDue to the beyond-classical capability of quantum computing, quantum machine learning is applied independently or embedded in classical models for decision making, especially in the field of finance. Fairness and other ethical issues are often one of the main concerns in decision making. In this work, we define a formal framework for the fairness verification and analysis of quantum machine learning decision models, where we adopt one of the most popular notions of fairness in the literature based on the intuition—any two similar individuals must be treated similarly and are thus unbiased. We show that quantum noise can improve fairness and develop an algorithm to check whether a (noisy) quantum machine learning model is fair. In particular, this algorithm can find bias kernels of quantum data (encoding individuals) during checking. These bias kernels generate infinitely many bias pairs for investigating the unfairness of the model. Our algorithm is designed based on a highly efficient data structure—Tensor Networks—and implemented on Google’s TensorFlow Quantum. The utility and effectiveness of our algorithm are confirmed by the experimental results, including income prediction and credit scoring on real-world data, for a class of random (noisy) quantum decision models with 27 qubits ($$2^{27}$$ 2 27 -dimensional state space) tripling ($$2^{18}$$ 2 18 times more than) that of the state-of-the-art algorithms for verifying quantum machine learning models.
Conference papers on the topic "Quantum space-times":
1
Hiley, B. J. "Quantum Space-Times: An Introduction to “Algebraic Quantum Mechanics and Pregeometry”." In QUANTUM THEORY: Reconsideration of Foundations - 3. AIP, 2006. http://dx.doi.org/10.1063/1.2158734.
2
CHAICHIAN, M., A. DEMICHEV, and P. PREŠNAJDER. "QUANTUM FIELD THEORY ON NONCOMMUTATIVE SPACE-TIMES: THE RELATION BETWEEN ULTRAVIOLET BEHAVIOUR AND TOPOLOGY." In Proceedings of XIV Max Born Symposium. WORLD SCIENTIFIC, 2000. http://dx.doi.org/10.1142/9789812793263_0004.
3
Plyavenek, A. G., and A. V. Lyubarjikii. "Carrier Capture and Escape in InGaAs/InGaAsP Quantum Well Lasers: Effect of Space Charge." In The European Conference on Lasers and Electro-Optics. Washington, D.C.: Optica Publishing Group, 1996. http://dx.doi.org/10.1364/cleo_europe.1996.ctuh4.
Abstract:
Key factors determining the speed of QW lasers are total carrier capture time and the ratio of the capture to escape times [1]. Usually these transport parameters are calculated under flat band conditions [2]. However, the accumulation of positive charge in QW region of InGaAs/InGaAsP lasers gives rise to significant modification of conduction and valence band profiles [3]. In this report we present the results of self-consistent calculations of effective electron capture and escape times in SCH InGaAs/InGaAsP QW laser structures taking into account band bending effects. We show that these lime constants are strongly affected by new intersubband transitions involved in capture processes due to appearance of new bound electron states in the presence of space charge.
4
Wang, Yan. "Accelerating Stochastic Dynamics Simulation With Continuous-Time Quantum Walks." In ASME 2016 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/detc2016-59420.
Abstract:
Stochastic diffusion is a general phenomenon observed in various national and engineering systems. It is typically modeled by either stochastic differential equation (SDE) or Fokker-Planck equation (FPE), which are equivalent approaches. Path integral is an accurate and effective method to solve FPEs. Yet, computational efficiency is the common challenge for path integral and other numerical methods, include time and space complexities. Previously, one-dimensional continuous-time quantum walk was used to simulate diffusion. By combining quantum diffusion and random diffusion, the new approach can accelerate the simulation with longer time steps than those in path integral. It was demonstrated that simulation can be dozens or even hundreds of times faster. In this paper, a new generic quantum operator is proposed to simulate drift-diffusion processes in high-dimensional space, which combines quantum walks on graphs with traditional path integral approaches. Probability amplitudes are computed efficiently by spectral analysis. The efficiency of the new method is demonstrated with stochastic resonance problems.
5
Prevenslik, Thomas. "Heat Transfer in Nanoelectronics by Quantum Mechanics." In ASME 2013 International Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Microsystems. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/ipack2013-73173.
Abstract:
Today, the transient Fourier heat conduction equation is not considered valid for the derivation of temperatures from the dissipation of Joule heat in nanoelectronics because the dimension of the circuit element is comparable to the mean free path of phonon energy carriers. Instead, the Boltzmann transport equation (BTE) for ballistic transport based on the scattering of phonons within the element is thought to govern heat transfer. However, phonons respond at acoustic frequencies in times on the order of 10–100 ps, and therefore the BTE would not have meaning if the Joule heat is conserved by a faster mechanism. Unlike phonons with response times limited by acoustic frequencies, heat transfer in nanoelectronics based on QED induced heat transfer conserves Joule heat in times < 1 fs by the creation of EM radiation at optical frequencies. QED stands for quantum electrodynamics. In effect, QED heat transfer negates thermal conduction in nanoelectronics because Joule heat is conserved well before phonons respond. QED induced heat transfer finds basis in Planck’s QM given by the Einstein-Hopf relation in terms of temperature and EM confinement of the atom as a harmonic oscillator. QM stands for quantum mechanics and EM for electromagnetic. Like the Fourier equation, the BTE is based on classical physics allowing the atom in nanoelectronic circuit elements to have finite heat capacity, thereby conserving Joule heat by an increase in temperature. QM differs by requiring the heat capacity of the atom to vanish. Conservation of Joule heat therefore proceeds by QED inducing the creation of excitons (hole and electron pairs) inside the circuit element by the frequency up-conversion of Joule heat to the element’s TIR confinement frequency. TIR stands for total internal reflection. Under the electric field across the element, the excitons separate to produce a positive space charge of holes that reduce the electrical resistance or upon recombination are lost by the emission of EM radiation to the surroundings. TIR confinement of EM radiation is the natural consequence of the high surface to volume ratio of the nanoelectronic circuit elements that concentrates Joule heat almost entirely in their surface, the surfaces coinciding with the TIR mode shape of the QED radiation. TIR confinement is not permanent, present only during the absorption of Joule heat. Charge creation aside, QM requires nanoelectronics circuit elements to remain at ambient temperature while dissipating Joule heat by QED radiation to the surroundings. Hot spots do not occur provided the RI of the circuit element is greater than the substrate or surroundings. RI stands for refractive index. In this paper, QED radiation is illustrated with memristors, PC-RAM devices, and 1/ f noise in nanowires, the latter of interest as the advantage of QM in avoiding hot spots in nanoelectronics may be offset by the noise from the holes created in the circuit elements by QED induced radiation.
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Slosser, John, T. A. B. Kennedy, and P. Meystre. "Decay of number-state superpositions in a micromaser." In OSA Annual Meeting. Washington, D.C.: Optica Publishing Group, 1988. http://dx.doi.org/10.1364/oam.1988.ms3.
Abstract:
Coherent superpositions of quantum states are very sensitive to coupling to the environment. The fluctuations associated with this coupling tend to wash out quantum phases, so that in practice only quantum mixtures are observed at the macroscopic level. This problem has been the object of recent interest in connection with measurement theory (Schrodinger cat). Theoretical predictions indicate that the decay of quantum coherences in the so-called pointer basis is amplified by a factor proportional to a measure of the distance in Hilbert space between the states. Micromasers offer a possible experimental tool to investigate the decay of such coherences. Theoretical studies of a lossless version of the micromaster have shown the existence of trapping states | n q 〉 of the cavity mode. These number states are such that atoms injected in the upper state into the cavity experience a 2qπ interaction with the field. Cavity states of the form | ψ 〉 = Σ q C q | n q 〉 are easily shown to be dynamic steady states of the system. Number states are not a pointer basis for the micromaser, and our theoretical results will evidence the qualitative difference in the nature of coherence decay between this and previously studied cases. Because the decay times of micromaser cavities are typically of the order of hundreds of milliseconds, our results should be amenable to experimental verification.
7
Nolte, D. D., R. M. Brubaker, M. R. Melloch, J. M. Woodall, and S. J. Ralph. "High-density holographic storage based on nanometer-size arsenic clusters in GaAs." In OSA Annual Meeting. Washington, D.C.: Optica Publishing Group, 1992. http://dx.doi.org/10.1364/oam.1992.tuvv7.
Abstract:
Nanometer-size arsenic clusters in a GaAs matrix have large capacities to trap photocarriers and to store charge. The material is prepared by low-temperature-growth (LTG) of molecular beam epitaxy (MBE) GaAs. We demonstrate that the thin films can be used as a high-density optical storage medium. The material exhibits an unexpected large electro-optic effect at room temperature for photon energies close to the bandgap. This effect is attributed to quantum effects of the mesoscopic clusters. Charge storage and electro-optic properties combine to produce a low-laser-power high-density holographic storage medium. The ultra-fast lifetimes of the photogenerated carriers produce excellent spatial resolution during the writing of holographic space-charge gratings. Fringe spacings as small as 6000 Å can be supported in this material, yielding two-dimensional optical data density greater than 108 bits/cm2. The saturation intensity is 10 mW/cm2 with a device storage time of 2 ms. With additional processing, fringe spacings as small as 2000 Å should be possible, with storage times approaching minutes.
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Jasmin, Serge, and Nakita Vodjdani. "Microwave Waveguide Photodiodes with Distributed Absorption for High Power Applications." In The European Conference on Lasers and Electro-Optics. Washington, D.C.: Optica Publishing Group, 1996. http://dx.doi.org/10.1364/cleo_europe.1996.ctho5.
Abstract:
The wide developement of analog radio frequency (RF) optical fiber links for optically fed wireless communication systems and phased array antennas is partly conditioned by the availability of high speed, high efficiency photodetectors which can also deliver high RF power. Lumped or travelling-wave waveguide PIN photodetectors (WGPDs) [1,2] can achieve both high quantum efficiency and high bandwidth without any limitations in bandwidth efficiency product as in conventional PD. However in this WGPDs, carriers are generated in the first ten microns. As a consequence, under high illumination, the high photocarriers density in this small surface area, by space charge effects, modifies the internal electric field which in turn governs the carriers transport. This field screening induces non linearities of the electrical response of the PD for high optical power, and limits the maximum RF power which can be delivered. For higher power capabilities, diluted travelling-wave detectors (TWDs) have been proposed [3,4]. In order to further improve the power handling of the detectors and reduce the space charge effects, we propose and analyze a new microwave WGPD which distributes absorption over the maximum junction area available. The structure is based on a diluted singlemode WG with coupling and quantum efficiencies > 90% and can handle both high optical and electrical power. The photocarriers density is maintained constant along the whole propagation length of the diode (instead of being exponential) by controling and tailoring the modal absorption coefficient αΓ(z) along the axis of propagation (Fig.l). This design applies to lumped WGPDs as well as TWDs. For the distributed absorption WGPD presented here, the depleted region consists of a thin InGaAsP active layer sandwiched between transparent WG and contact layers and αΓ(z) can be varied by a factor of 10 by changing the WG ridge width from 2 to 4 µm. For a same junction area, the maximum RF output power can be 4 to 9 times higher for distributed absorption WGPDs as compared to diluted WGPDs [3,4] (lumped or TWDs). The structures are compared by using a drift-diffusion model which takes into account the heterointerfaces, device depolarization due to current flow in the load circuit and calculates the electric field in the depleted region in the linear regime (50 < E< 250kV/cm). At a given cut off frequency the figure of merit F is defined as the ratio of the maximum RF power to the incident optical power. F is optimized by choosing the maximum depleted region thickness (transit time limitation), the maximum junction area (RC time constant limitation for lumped detectors and 5 times more for TWDs) and by varying the reverse voltage and the optical power. Details of the design and performances of distributed absorption WGPD with coplanar transmission line will be presented in the conference.
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Oberli, D. Y., J. Shah, T. C. Damen, C. W. Tu, and D. A. B. Miller. "Electron Tunneling Times in Coupled Quantum Wells." In Quantum Wells for Optics and Opto-Electronics. Washington, D.C.: Optica Publishing Group, 1989. http://dx.doi.org/10.1364/qwoe.1989.wd3.
Abstract:
The work by Esaki and Tsu on tunneling in superlattices1 has generated a considerable interest for the potential application of tunneling to real devices. The rapid progress of epitaxial growth techniques has led to the creation of novel semiconductor structures which exhibit quantum-size effects and tunneling such as the double-barrier resonnant tunneling structures or the superlattice p-i-n diodes2. Transport studies in these structures demonstrated Bloch transport through the superlattice minibands3, negative differential resistance in double barrier diodes4, field induced localization5. More recently, optical measurements have been performed in double barrier structures in order to gain some insight on space-charge buildup6 and escape rates7.
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Medlar, Michael P., and Edward C. Hensel. "Validation of a Physics Based Three Phonon Scattering Algorithm Implemented in the Statistical Phonon Transport Model." In ASME 2020 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/imece2020-23307.
Abstract:
Abstract Three phonon scattering is the primary mechanism by which phonon transport is impeded in insulating and semiconducting bulk materials. Accurate computational modeling of this scattering mechanism is required for high fidelity simulations of thermal transport across the ballistic (quantum mechanics) to Fourier (continuum mechanics) range of behavior. Traditional Monte Carlo simulations of phonon transport use a scaling factor such that each scattering event is considered representative of a large number of phonons, often on the order of 104 physical phonons per simulated event. The ability to account for every phonon scattering event is desirable to enhance model fidelity. A physics-based model using time dependent perturbation theory (Fermi’s Golden Rule) is implemented to compute three phonon scattering rates for each permissible phonon interaction subject to selection rules. The strength of the interaction is based on use of a Gruneisen-like parameter. Both Type I and Type II scattering rates are computed for the allowable interactions that conserve energy and momentum (up to the addition of a reciprocal lattice vector) on a given discretization of momentum space. All of the phonons in the computational domain are represented and phonon populations are updated in momentum space and real space based on the computed number of phonons involved in given scattering events. The computational algorithm is tested in an adiabatic single cell of silicon of dimension 100 × 100 × 100 nm at a nominal temperature of 500 Kelvin containing approximately 108 fully anisotropic phonons. The results indicate that phonon populations return to equilibrium if artificially displaced from that condition. Two approaches are introduced to model the relaxation time of phonon states: the single mode relaxation time (SMRT) which is consistent with the underlying assumptions for previously reported theoretical estimates, and the multi model relaxation time (MMRT) which is more consistent with in-situ conditions. The trends meet physical expectations and are comparable to other literature results. In addition, an estimate of error associated with the relaxation times is presented using the statistical nature of the model. The three phonon scattering model presented provides a high fidelity representation of this physical process that improves the computational prediction of anisotropic phonon transport in the statistical phonon transport model.
Reports on the topic "Quantum space-times":
1
Perdigão, Rui A. P. Strengthening Multi-Hazard Resilience with Quantum Aerospace Systems Intelligence. Synergistic Manifolds, January 2024. http://dx.doi.org/10.46337/240301.
Abstract:
The present work further enhances and deploys our Quantum Aerospace Systems Intelligence technologies (DOI: 10.46337/quasi.230901) onto Multi-Hazard risk assessment and action, from sensing and prediction to modelling, decision support and active response, towards strengthening its fundamental knowledge, awareness and resilience in the face of multi-domain challenges. Moreover, it introduces our updated post-quantum aerospace engineering ecosystem for empowering active system dynamic capabilities to mitigate or even counter multi-hazard threats from space, leveraging our high energy technological physics solutions acting across coevolutionary space-times. These developments are further articulated with our latest Synergistic Nonlinear Quantum Wave Intelligence Networks suite of technologies (DOI: 10.46337/240118), vastly extending the operational capabilities of novel quantum and post-quantum systems to critically adverse thermodynamic conditions e.g. those pertaining situational action across real-world environmental and security theaters of operation.