Artículos de revistas: "Quantum thermal field theory"

1

Bros, Jacques. "Thermal Aspects in Quantum Field Theory". Annales Henri Poincaré 4, S2 (diciembre de 2003): 863–80. http://dx.doi.org/10.1007/s00023-003-0967-1.

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2

Rahaman, Mahfuzur, Trambak Bhattacharyya y Jan-e. Alam. "Phenomenological Tsallis distribution from thermal field theory". International Journal of Modern Physics A 36, n.º 20 (14 de julio de 2021): 2150154. http://dx.doi.org/10.1142/s0217751x21501542.

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Classical and quantum Tsallis distributions have been widely used in many branches of natural and social sciences. But, the quantum field theory of the Tsallis distributions is relatively a less explored arena. In this paper, we derive the expression for the thermal two-point functions in the Tsallis statistics with the help of the corresponding statistical mechanical formulations. We show that the quantum Tsallis distributions used in the literature appear in the thermal part of the propagator much in the same way the Boltzmann–Gibbs distributions appear in the conventional thermal field theory. As an application of our findings, we calculate the thermal mass in the [Formula: see text] scalar field theory within the realm of the Tsallis statistics.

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3

HENNING, P. A., K. NAKAMURA y Y. YAMANAKA. "THERMAL FIELD THEORY IN NON-EQUILIBRIUM STATES". International Journal of Modern Physics B 10, n.º 13n14 (30 de junio de 1996): 1599–614. http://dx.doi.org/10.1142/s0217979296000696.

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Conventional transport theory is not really applicable to nonequilibrium systems which exhibit strong quantum effects. We present two different approaches to overcome this problem. Firstly we point out how transport equations may be derived that incorporate a nontrivial spectral function as a typical quantum effect, and test this approach in a toy model of a strongly interacting degenerate plasma. Secondly we explore a path to include nonequilibrium effects into quantum field theory through momentum mixing transformations in Fock space. Although the two approaches are completely orthogonal, they lead to the same coherent conclusion.

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4

Liao, Sen-Ben, Janos Polonyi y Dapeng Xu. "Quantum and thermal fluctuations in field theory". Physical Review D 51, n.º 2 (15 de enero de 1995): 748–64. http://dx.doi.org/10.1103/physrevd.51.748.

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5

Braga de Góes Vasconcellos, João, Nicolò Drago y Nicola Pinamonti. "Equilibrium States in Thermal Field Theory and in Algebraic Quantum Field Theory". Annales Henri Poincaré 21, n.º 1 (28 de octubre de 2019): 1–43. http://dx.doi.org/10.1007/s00023-019-00859-3.

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6

CHU, H. y H. UMEZAWA. "A UNIFIED FORMALISM OF THERMAL QUANTUM FIELD THEORY". International Journal of Modern Physics A 09, n.º 14 (10 de junio de 1994): 2363–409. http://dx.doi.org/10.1142/s0217751x94000960.

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We present a comprehensive review of the most fundamental and practical aspects of thermo-field dynamics (TFD), including some of the most recent developments in the field. To make TFD fully consistent, some suitable changes in the structure of the thermal doublets and the Bogoliubov transformation matrices have been made. A close comparison between TFD and the Schwinger-Keldysh closed time path formalism (SKF) is presented. We find that TFD and SKF are in many ways the same in form; in particular, the two approaches are identical in stationary situations. However, TFD and SKF are quite different in time-dependent nonequilibrium situations. The main source of this difference is that the time evolution of the density matrix itself is ignored in SKF while in TFD it is replaced by a time-dependent Bogoliubov transformation. In this sense TFD is a better candidate for time-dependent quantum field theory. Even in equilibrium situations, TFD has some remarkable advantages over the Matsubara approach and SKF, the most notable being the Feynman diagram recipes, which we will present. We will show that the calculations of two-point functions are simplified, instead of being complicated, by the matrix nature of the formalism. We will present some explicit calculations using TFD, including space-time inhomogeneous situations and the vacuum polarization in equilibrium relativistic QED.

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7

Kovalchuk, E. y R. Kobes. "Bose-Einstein condensates and thermal field theory". Canadian Journal of Physics 85, n.º 6 (1 de junio de 2007): 647–52. http://dx.doi.org/10.1139/p07-058.

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We consider a homogeneous nonideal Bose gas in equilibrium at nonzero temperature below the critical temperature Tc in the framework of thermal field theory. Quantum corrections up to second order are calculated, which are shown to be crucial in obtaining the correct behavior in thermodynamic quantities such as the specific heat. PACS Nos.: 67.40.–w, 11.10.Wx

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8

Mirón Granese, Nahuel, Alejandra Kandus y Esteban Calzetta. "Field Theory Approaches to Relativistic Hydrodynamics". Entropy 24, n.º 12 (7 de diciembre de 2022): 1790. http://dx.doi.org/10.3390/e24121790.

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Just as non-relativistic fluids, oftentimes we find relativistic fluids in situations where random fluctuations cannot be ignored, with thermal and turbulent fluctuations being the most relevant examples. Because of the theory’s inherent nonlinearity, fluctuations induce deep and complex changes in the dynamics of the system. The Martin–Siggia–Rose technique is a powerful tool that allows us to translate the original hydrodynamic problem into a quantum field theory one, thus taking advantage of the progress in the treatment of quantum fields out of equilibrium. To demonstrate this technique, we shall consider the thermal fluctuations of the spin two modes of a relativistic fluid, in a theory where hydrodynamics is derived by taking moments of the Boltzmann equation under the relaxation time approximation.

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9

Fulling, S. A., A. G. S. Landulfo y G. E. A. Matsas. "The relation between quantum and classical field theory with a classical source". Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 476, n.º 2243 (noviembre de 2020): 20200656. http://dx.doi.org/10.1098/rspa.2020.0656.

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Classical field theory is about fields and how they behave in space–time. Quantum field theory, in practice, usually seems to be about particles and how they scatter. Nevertheless, classical fields must emerge from quantum field theory in appropriate limits, and Michael Duff showed how this happens for the Schwarzschild solution in perturbative quantum gravity. In a series of papers, we and others have shown how classical radiation from an accelerated charge emerges from quantum field theory when the Unruh thermal effect is taken into account. Here, we sharpen those conclusions by showing that, even at finite times, the quantum picture is meaningful and is in close agreement with the classical picture.

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10

CHU, H. y H. UMEZAWA. "STABLE QUASIPARTICLE PICTURE IN THERMAL QUANTUM FIELD PHYSICS". International Journal of Modern Physics A 09, n.º 10 (20 de abril de 1994): 1703–29. http://dx.doi.org/10.1142/s0217751x9400073x.

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It is well known that physical particles are thermally dissipative at finite temperature. In this paper we reformulate both the equilibrium and nonequilibrium thermal field theories in terms of stable quasiparticles. We will redefine the thermal doublets, the double tilde conjugation rules and the thermal Bogoliubov transformations so that our theory can be consistent for most general situations. All operators, including the dissipative physical particle operators, are realized in a Fock space defined by the stable quasiparticles. The propagators of the physical particles are expressed in terms of the operators of such stable quasiparticles, which is a simple diagonal matrix with the diagonal elements being the temporal step functions, same as the propagators in the usual quantum field theory without thermal degrees of freedom. The proper self-energies are also expressed in terms of these stable quasiparticle propagators. This formalism inherits the definition of on-shell self-energy in the usual quantum field theory. With this definition, a self-consistent renormalization is formulated which leads to quantum Boltzmann equation and the entropy law. With the aid of a doublet vector algebra we have an extremely simple recipe for computing Feynman diagrams. We apply this recipe to several examples of equilibrium and nonequilibrium two-point functions, and to the kinetic equation for the particle numbers.

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11

CHU, H. y H. UMEZAWA. "RENORMALIZATION AND BOLTZMANN EQUATIONS IN THERMAL QUANTUM FIELD THEORY". International Journal of Modern Physics A 10, n.º 11 (30 de abril de 1995): 1693–700. http://dx.doi.org/10.1142/s0217751x95000814.

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The renormalization scheme in nonequilibrium thermal quantum field theories is reexamined. Instead of the self-energy diagonalization scheme, we propose to diagonalize Green’s function at equal time. This eliminates the problem of on-shell definition related to time-dependent energies and spatially inhomogeneous situations, and yields a Boltzmann equation that contains memory effect. The new diagonalization scheme and the derivation of the Boltzmann equation from it can be applied to any thermal situation. It allows the treatment of a nonequilibrium problem beyond perturbational calculations in a self-consistent manner. The results are applicable to both thermo field dynamics and the closed time path formalism.

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12

Baier, R., M. Dirks, K. Redlich y D. Schiff. "Thermal photon production rate from nonequilibrium quantum field theory". Physical Review D 56, n.º 5 (1 de septiembre de 1997): 2548–54. http://dx.doi.org/10.1103/physrevd.56.2548.

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13

Jäkel, Christian D. y Walter F. Wreszinski. "A Goldstone theorem in thermal relativistic quantum field theory". Journal of Mathematical Physics 52, n.º 1 (enero de 2011): 012302. http://dx.doi.org/10.1063/1.3526961.

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14

Umezawa, H. y Y. Yamanaka. "Micro, macro and thermal concepts in quantum field theory". Advances in Physics 37, n.º 5 (octubre de 1988): 531–57. http://dx.doi.org/10.1080/00018738800101429.

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15

Chu, H., Y. C. Chang, H. Umezawa y F. C. Khanna. "Boson condensations in real time thermal quantum field theory". Physics Letters A 201, n.º 4 (mayo de 1995): 353–58. http://dx.doi.org/10.1016/0375-9601(95)00290-j.

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16

Kotecha, Isha. "Thermal Quantum Spacetime". Universe 5, n.º 8 (12 de agosto de 2019): 187. http://dx.doi.org/10.3390/universe5080187.

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The intersection of thermodynamics, quantum theory and gravity has revealed many profound insights, all the while posing new puzzles. In this article, we discuss an extension of equilibrium statistical mechanics and thermodynamics potentially compatible with a key feature of general relativity, background independence; and we subsequently use it in a candidate quantum gravity system, thus providing a preliminary formulation of a thermal quantum spacetime. Specifically, we emphasise an information-theoretic characterisation of generalised Gibbs equilibrium that is shown to be particularly suited to background independent settings, and in which the status of entropy is elevated to being more fundamental than energy. We also shed light on its intimate connections with the thermal time hypothesis. Based on this, we outline a framework for statistical mechanics of quantum gravity degrees of freedom of combinatorial and algebraic type, and apply it in several examples. In particular, we provide a quantum statistical basis for the origin of covariant group field theories, shown to arise as effective statistical field theories of the underlying quanta of space in a certain class of generalised Gibbs states.

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17

Grandou, Thierry y Ralf Hofmann. "Thermal Ground State and Nonthermal Probes". Advances in Mathematical Physics 2015 (2015): 1–8. http://dx.doi.org/10.1155/2015/197197.

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The Euclidean formulation of SU(2) Yang-Mills thermodynamics admits periodic, (anti)self-dual solutions to the fundamental, classical equation of motion which possess one unit of topological charge: (anti)calorons. A spatial coarse graining over the central region in a pair of such localised field configurations with trivial holonomy generates an inert adjoint scalar fieldϕ, effectively describing the pure quantum part of the thermal ground state in the induced quantum field theory. Here we show for the limit of zero holonomy how (anti)calorons associate a temperature independent electric permittivity and magnetic permeability to the thermal ground state ofSU2CMB, the Yang-Mills theory conjectured to underlie the fundamental description of thermal photon gases.

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18

Greenberg, O. W. "N-quantum approach to the BCS theory of superconductivity". Canadian Journal of Physics 72, n.º 9-10 (1 de septiembre de 1994): 574–77. http://dx.doi.org/10.1139/p94-073.

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A method of general applicability to the solution of second-quantized field theories at finite temperature is illustrated using the BCS (Bardeen–Cooper–Schrieffer) model of superconductivity. Finite-temperature field theory is treated using the thermo field-theory formalism of Umezawa and collaborators. The solution of the field theory uses an expansion in thermal modes analogous to the Haag expansion in asymptotic fields used in the N-quantum approximation at zero temperature. The lowest approximation gives the usual gap equation.

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19

Klimchitskaya, G. L. "Quantum field theory of the Casimir force for graphene". International Journal of Modern Physics A 31, n.º 02n03 (20 de enero de 2016): 1641026. http://dx.doi.org/10.1142/s0217751x16410268.

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We present theoretical description of the Casimir interaction in graphene systems which is based on the Lifshitz theory of dispersion forces and the formalism of the polarization tensor in (2+1)-dimensional space-time. The representation for the polarization tensor of graphene allowing the analytic continuation to the whole plane of complex frequencies is given. This representation is used to obtain simple asymptotic expressions for the reflection coefficients at all Matsubara frequencies and to investigate the origin of large thermal effect in the Casimir force for graphene. The developed theory is shown to be in a good agreement with the experimental data on measuring the gradient of the Casimir force between a Au-coated sphere and a graphene-coated substrate. The possibility to observe the thermal effect for graphene due to a minor modification of the already existing experimental setup is demonstrated.

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20

FAN, HONG-YI y HUI WANG. "NEW APPLICATIONS OF <η| REPRESENTATION IN THERMAL FIELD STATISTICS". Modern Physics Letters B 14, n.º 15 (30 de junio de 2000): 553–62. http://dx.doi.org/10.1142/s0217984900000707.

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We derive <η| representation of density matrices ρ for radiation fields, where <η| is the newly established coherent thermal state [H.-Y. Fan and Y. Fan, Phys. Lett.A246, 242 (1998)] in thermal field dynamics. We then apply <η|ρ> to calculate thermal averages and develop the theory for the quantum phase space distributions. We also study the quantum master equations in the <η| representation and find it has similar evolving property to the coherent representation of a pure state.

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21

Carrington, M. E., R. Kobes, G. Kunstatter, D. Pickering y E. Vaz. "Equilibration in an interacting field theory". Canadian Journal of Physics 80, n.º 9 (1 de septiembre de 2002): 987–93. http://dx.doi.org/10.1139/p02-065.

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We use a combination of perturbation theory and numerical techniques to study the equilibration of two interacting fields that are initially at thermal equilibrium at different temperatures. Using standard rules of quantum field theory, we examine the master equations that describe the time evolution of the distribution functions for the two coupled systems. By making a few reasonable assumptions we reduce the resulting coupled integral/differential equations to a pair of differential equations that can be solved numerically relatively easily and which give physically sensible results. PACS No.: 11.10W

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22

BUCHHOLZ, D. y C. D’ANTONI. "PHASE SPACE PROPERTIES OF CHARGED FIELDS IN THEORIES OF LOCAL OBSERVABLES". Reviews in Mathematical Physics 07, n.º 04 (mayo de 1995): 527–57. http://dx.doi.org/10.1142/s0129055x95000219.

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Within the setting of algebraic quantum field theory a relation between phase-space properties of observables and charged fields is established. These properties are expressed in terms of compactness and nuclearity conditions which are the basis for the characterization of theories with physically reasonable causal and thermal features. Relevant concepts and results of phase space analysis in algebraic quantum field theory are reviewed and the underlying ideas are outlined.

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23

Brandt, F. T., J. Frenkel, S. Martins-Filho, D. G. C. McKeon y G. S. S. Sakoda. "Thermal gauge theories with Lagrange multiplier fields". Canadian Journal of Physics 100, n.º 3 (marzo de 2022): 139–44. http://dx.doi.org/10.1139/cjp-2021-0248.

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We study the Yang–Mills theory and quantum gravity at finite temperature, in the presence of Lagrange multiplier fields. These restrict the path integrals to field configurations, which obey the classical equations of motion. This has the effect of doubling the usual one-loop thermal contributions and of suppressing all radiative corrections at higher-loop order. Such theories are renormalizable at all temperatures. Some consequences of this result in quantum gravity are briefly examined.

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24

VERCH, RAINER y REINHARD F. WERNER. "DISTILLABILITY AND POSITIVITY OF PARTIAL TRANSPOSES IN GENERAL QUANTUM FIELD SYSTEMS". Reviews in Mathematical Physics 17, n.º 05 (junio de 2005): 545–76. http://dx.doi.org/10.1142/s0129055x05002364.

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Criteria for distillability, and the property of having a positive partial transpose, are introduced for states of general bipartite quantum systems. The framework is sufficiently general to include systems with an infinite number of degrees-of-freedom, including quantum fields. We show that a large number of states in relativistic quantum field theory, including the vacuum state and thermal equilibrium states, are distillable over subsystems separated by arbitrary spacelike distances. These results apply to any quantum field model. It will also be shown that these results can be generalized to quantum fields in curved spacetime, leading to the conclusion that there is a large number of quantum field states which are distillable over subsystems separated by an event horizon.

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25

Guo, Xiao-Kan. "Thermofield double states in group field theory". International Journal of Modern Physics A 36, n.º 02 (20 de enero de 2021): 2150008. http://dx.doi.org/10.1142/s0217751x21500081.

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Group field theories are higher-rank generalizations of matrix/tensor models, and encode the simplicial geometries of quantum gravity. In this paper, we study the thermofield double states in group field theories. The starting point is the equilibrium Gibbs states in group field theory recently found by Kotecha and Oriti, based on which we construct the thermofield double state as a “thermal” vacuum respecting the Kubo–Martin–Schwinger condition. We work with the Weyl [Formula: see text]-algebra of group fields, and a particular type of thermofield double states with single type of symmetry is obtained from the squeezed states on this Weyl algebra. The thermofield double states, when viewed as states on the group field theory Fock vacuum, are condensate states at finite flow parameter [Formula: see text]. We suggest that the equilibrium flow parameters [Formula: see text] of this type of thermofield double states in the group field theory condensate pictures of black hole horizon and quantum cosmology are related to the inverse temperatures in gravitational thermodynamics.

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26

WETTERICH, CHRISTOF. "EFFECTIVE AVERAGE ACTION IN STATISTICAL PHYSICS AND QUANTUM FIELD THEORY". International Journal of Modern Physics A 16, n.º 11 (30 de abril de 2001): 1951–82. http://dx.doi.org/10.1142/s0217751x01004591.

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An exact renormalization group equation describes the dependence of the free energy on an infrared cutoff for the quantum or thermal fluctuations. It interpolates between the microphysical laws and the complex macroscopic phenomena. We present a simple unified description of critical phenomena for O(N)-symmetric scalar models in two, three or four dimensions, including essential scaling for the Kosterlitz-Thouless transition.

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27

Bischer, Ingolf, Thierry Grandou y Ralf Hofmann. "Perturbative Peculiarities of Quantum Field Theories at High Temperatures". Universe 5, n.º 3 (14 de marzo de 2019): 81. http://dx.doi.org/10.3390/universe5030081.

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Revisiting the fast fermion damping rate calculation in a thermalized QED and/or QCD plasma in thermal equilibrium at four-loop order, focus is put on a peculiar perturbative structure which has no equivalent at zero-temperature. Not surprisingly, and in agreement with previous C ☆ -algebraic analyses, this structure renders the use of thermal perturbation theory more than questionable.

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28

FATEEV, V. A. y A. B. ZAMOLODCHIKOV. "CONFORMAL FIELD THEORY AND PURELY ELASTIC S-MATRICES". International Journal of Modern Physics A 05, n.º 06 (20 de marzo de 1990): 1025–48. http://dx.doi.org/10.1142/s0217751x90000477.

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Particular perturbations of a 2D Conformal Field Theory leading to Integrable massive Quantum Field Theories are examined. The mass spectra and S-matrices for some models, including the field theory of the Ising Model with magnetic field and “thermal” deformations of the tricritical Ising and 3-state Potts models, are proposed. The hidden Lie-algebraic structures of these spectra and their relation to the Toda systems are discussed.

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29

Epstein, Henri y Ugo Moschella. "Topological surprises in de Sitter QFT in two-dimensions". International Journal of Modern Physics A 33, n.º 34 (10 de diciembre de 2018): 1845009. http://dx.doi.org/10.1142/s0217751x18450094.

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Motivated by the study of soluble models of quantum field theory, we illustrate a new type of topological effect by comparing the constructions of canonical Klein–Gordon quantum fields on the two-dimensional de Sitter spacetime as opposed to its double covering. We show that while the commutators of the two fields coincide locally, the global topological differences make the theories drastically different. Many of the well-known features of de Sitter quantum field theory disappear. In particular, there is nothing like a Bunch–Davies vacuum. Correspondingly, even though the local horizon structure is the same for the two universes, there is no Hawking–Gibbons thermal state. Finally, there is no complementary series of fields.

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30

Zhou, Zhao-Yu, Guo-Xian Su, Jad C. Halimeh, Robert Ott, Hui Sun, Philipp Hauke, Bing Yang, Zhen-Sheng Yuan, Jürgen Berges y Jian-Wei Pan. "Thermalization dynamics of a gauge theory on a quantum simulator". Science 377, n.º 6603 (15 de julio de 2022): 311–14. http://dx.doi.org/10.1126/science.abl6277.

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Gauge theories form the foundation of modern physics, with applications ranging from elementary particle physics and early-universe cosmology to condensed matter systems. We perform quantum simulations of the unitary dynamics of a U(1) symmetric gauge field theory and demonstrate emergent irreversible behavior. The highly constrained gauge theory dynamics are encoded in a one-dimensional Bose-Hubbard simulator, which couples fermionic matter fields through dynamical gauge fields. We investigated global quantum quenches and the equilibration to a steady state well approximated by a thermal ensemble. Our work may enable the investigation of elusive phenomena, such as Schwinger pair production and string breaking, and paves the way for simulating more complex, higher-dimensional gauge theories on quantum synthetic matter devices.

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31

HÜFFEL, HELMUTH. "NONLINEAR PHENOMENA IN CANONICAL STOCHASTIC QUANTIZATION". International Journal of Bifurcation and Chaos 18, n.º 09 (septiembre de 2008): 2787–91. http://dx.doi.org/10.1142/s0218127408022019.

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Stochastic quantization provides a connection between quantum field theory and statistical mechanics, with applications especially in gauge field theories. Euclidean quantum field theory is viewed as the equilibrium limit of a statistical system coupled to a thermal reservoir. Nonlinear phenomena in stochastic quantization arise when employing nonlinear Brownian motion as an underlying stochastic process. We discuss a novel formulation of the Higgs mechanism in QED.

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32

PANCHAPAKESAN, N. "QUANTUM TUNNELLING OR THERMAL HOPPING". International Journal of Modern Physics B 14, n.º 19n20 (10 de agosto de 2000): 2109–16. http://dx.doi.org/10.1142/s0217979200001163.

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The nature of the transition from the quantum tunneling regime to the thermal hopping regime has importance in the study of condensed matter physics and cosmological phase transitions. It may also be of significance in collapse from quantum state to a classical state due to measurement (or loss of coherence due to some other process). We study this transition analytically in scalar field theory with a fourth order term. We obtain analytic bounce solutions which correctly give the action in thin and thick wall limits of the potential. We find that the transition is of the second order for the case of thick wall while it seems to be of first order for the case of thin wall.

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33

Corianò, Claudio, Mario Cretì y Stefania D’Agostino. "Quantum Field Theory and its Anomalies for Topological Matter". EPJ Web of Conferences 270 (2022): 00026. http://dx.doi.org/10.1051/epjconf/202227000026.

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Topology enters in quantum field theory (qft) in multiple forms: one of the most important, in non-abelian gauge theories, being in the identification of the θ vacuum in QCD. A very relevant aspect of this connection is through the phenomenon of chiral and conformal qft anomalies. It has been realized that a class of materials, comprising topological insulators and Weyl semimetals, also exhibit the phenomenon of anomalies, which are responsible for several exotic phenomena, such as the presence of edge currents, resilient under perturbations and scattering by impurities. Another example comes from the response functions of these materials under thermal and mechanical stresses, that may be performed using correlation functions of stress energy tensors in General Relativity. In this case the conformal anomaly plays an important role. We briefly illustrate some salient features of this correspondence, and the effective action describing the long-range interactions that may account for such topological effects.

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34

Solveen, Christoph. "Local thermal equilibrium in quantum field theory on flat and curved spacetimes". Classical and Quantum Gravity 27, n.º 23 (1 de noviembre de 2010): 235002. http://dx.doi.org/10.1088/0264-9381/27/23/235002.

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35

Kitamura, Toyoyuki. "A quantum field theory of thermal conductivity near the liquid-glass transition". Physica A: Statistical Mechanics and its Applications 272, n.º 3-4 (octubre de 1999): 330–57. http://dx.doi.org/10.1016/s0378-4371(99)00250-2.

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36

Ambruş, Victor E., Carl Kent y Elizabeth Winstanley. "Analysis of scalar and fermion quantum field theory on anti-de Sitter spacetime". International Journal of Modern Physics D 27, n.º 11 (agosto de 2018): 1843014. http://dx.doi.org/10.1142/s0218271818430149.

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We study vacuum and thermal expectation values of quantum scalar and Dirac fermion fields on anti-de Sitter (adS) spacetime. AdS spacetime is maximally symmetric and this enables expressions for the scalar and fermion vacuum Feynman Green’s functions to be derived in closed form. We employ Hadamard renormalization to find the vacuum expectation values (v.e.v.s). The thermal Feynman Green’s functions are constructed from the vacuum Feynman Green’s functions using the imaginary time periodicity/anti-periodicity property for scalars/fermions. Focusing on massless fields with either conformal or minimal coupling to the spacetime curvature (these two cases being the same for fermions) we compute the differences between the thermal expectation values and v.e.v.s. We compare the resulting energy densities, pressures and pressure deviators with the corresponding classical quantities calculated using relativistic kinetic theory.

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37

Niu, Ming-Li, Yue-Ming Wang y Zhi-Jian Li. "Estimation of light-matter coupling constant under dispersive interaction based on quantum Fisher information". Acta Physica Sinica 71, n.º 9 (2022): 090601. http://dx.doi.org/10.7498/aps.71.20212029.

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Quantum parameter estimation is one of the most important applications in quantum metrology. The basic theory of quantum parameter estimation－quantum Cramer-Rao bound－shows that the precision limit of quantum parameter estimation is directly related to quantum Fisher information. Therefore quantum Fisher information is extremely important in the quantum parameter estimation. In this paper we use quantum parameter estimation theory to estimate the coupling constant of the Jaynes-Cummings model with large detuning. The initial probing state is the direct product state of qubit and radiation field in which Fock state, thermal state and coherent state are taken into account respectively. We calculate the quantum Fisher information of the hybrid system as well as qubit and radiation field for each probing state after the parameter evolution under the Hamiltonian of the Jaynes-Cummings model with large detuning. The results show that the quantum Fisher information increases monotonically with the average photon number increasing. The optimal detection state is that when the qubit system is in the equal weight superposition of the ground and the excited state, at this time the quantum Fisher information always reaches a maximum value, When the radiation field of probing state is Fock state or the thermal state, the information about the estimated parameter is included only in the qubit. The estimation accuracy of the coupling constant with thermal state or coherent state is higher than that with Fock state.

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38

Ames, Benedikt, Edoardo G. Carnio, Vyacheslav N. Shatokhin y Andreas Buchleitner. "Theory of multiple quantum coherence signals in dilute thermal gases". New Journal of Physics 24, n.º 1 (1 de enero de 2022): 013024. http://dx.doi.org/10.1088/1367-2630/ac4054.

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Abstract Manifestations of dipole–dipole interactions in dilute thermal gases are difficult to sense because of strong inhomogeneous broadening. Recent experiments reported signatures of such interactions in fluorescence detection-based measurements of multiple quantum coherence (MQC) signals, with many characteristic features hitherto unexplained. We develop an original open quantum systems theory of MQC in dilute thermal gases, which allows us to resolve this conundrum. Our theory accounts for the vector character of the atomic dipoles as well as for driving laser pulses of arbitrary strength, includes the far-field coupling between the dipoles, which prevails in dilute ensembles, and effectively incorporates atomic motion via a disorder average. We show that collective decay processes—which were ignored in previous treatments employing the electrostatic form of dipolar interactions—play a key role in the emergence of MQC signals.

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39

Song, Tong-Qiang. "Quantum Fluctuation in Thermal Vacuum State for Nondissipative Mesoscopic Capacitance Coupling Circuit". Modern Physics Letters B 17, n.º 15 (30 de junio de 2003): 821–28. http://dx.doi.org/10.1142/s0217984903005779.

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40

PITAEVSKII, L. P. "TRAPPED BOSE GAS: MEAN-FIELD APPROXIMATION AND BEYOND". International Journal of Modern Physics B 13, n.º 05n06 (10 de marzo de 1999): 427–45. http://dx.doi.org/10.1142/s0217979299000333.

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The recent realization of Bose-Einstein condensation in atomic gases opens new possibilities for observation of macroscopic quantum phenomena. There are two important features of the system - weak interaction and significant spatial inhomogeneity. Because of this inhomogeneity a non-trivial "zeroth-order" theory exists, compared to the "first-order" Bogolubov theory. This theory is based on the mean-field Gross-Pitaevskii equation for the condensate ψ-function. The equation is classical in its essence but contains the ℏ constant explicitly. Phenomena such as collective modes, interference, tunneling, Josephson-like current and quantized vortex lines can be described using this equation. The study of deviations from the zeroth-order theory arising from zero-point and thermal fluctuations is also of great interest. Thermal fluctuations are described by elementary excitations which define the thermodynamic behaviour of the system and result in Landau-type damping of collective modes. Fluctuations of the phase of the condensate wave function restrict the monochromaticity of the Josephson current. Fluctuations of the numbers of quanta result in the quantum collapse-revival of the collective oscillations. This phenomenon is considered in some details. Collapse time for the JILA experimental conditions turns out to be of the order of seconds.

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41

VENKATARATNAM, K. K. y P. K. SURESH. "OSCILLATORY PHASE OF NONCLASSICAL THERMAL INFLATON IN FRW UNIVERSE". International Journal of Modern Physics D 19, n.º 07 (julio de 2010): 1147–95. http://dx.doi.org/10.1142/s0218271810017184.

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A minimally coupled nonclassical homogeneous scalar field is examined in the flat FRW universe in the semiclassical theory of gravity. Particle production in thermal coherent and squeezed states is studied for the flat FRW universe, in the oscillatory phase of the inflaton. Solutions for the semiclassical Friedmann equations are obtained in the thermal nonclassical states. Validity of the semiclassical theory is examined in the thermal coherent and squeezed states in the oscillatory phase of inflaton. Particle creation can be enhanced due to thermal and quantum effects. Quantum fluctuations of the inflaton in thermal coherent and squeezed state formalisms are also studied. Classical gravity differ from semiclassical gravity in the thermal coherent state only by an amplitude factor.

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42

PANG, QIANJUN. "THE DENSITY MATRIX FOR AN ELECTRON CONFINED IN QUANTUM DOTS UNDER A UNIFORM MAGNETIC FIELD". International Journal of Modern Physics B 20, n.º 16 (30 de junio de 2006): 2295–303. http://dx.doi.org/10.1142/s0217979206034637.

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By using unitary transformation and representation theory of quantum mechanics, we obtain two forms of density matrix respectively in (x1, p2) and (x1, x2) representations for an electron, with an anisotropic effective mass, confined in quantum dots under a uniform magnetic field (UMF). We find that both forms of density matrix can play an implemental role in the thermodynamical calculation. But, in order to calculate thermal average of angular momentum in z direction for this system, the density matrix in (x1, p2) representations is a more convenient form. When the confinement to electron in quantum dots disappears, we encounter a divergence problem of thermal average for some physical quantities. However, in the calculation of the thermal average of Hamiltonian, these divergent quantities cancelled each other out. And we eventually obtain a reasonable result.

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43

Банная, В. Ф. y Е. В. Никитина. "Разогрев электронов в чистом Ge в квантовом магнитном поле при термическом возбуждении носителей заряда". Физика и техника полупроводников 54, n.º 3 (2020): 221. http://dx.doi.org/10.21883/ftp.2020.03.49021.9282.

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The results of an experimental study on charge carriers heating by an electric field (E) in pure Ge in a quantum magnetic field (H) at (E⊥H) at low temperatures (T=4,2;1,8 K) under thermal excitation are considered. It is shown that the dependence of E and H thermal ionization coefficient affects the average carrier lifetime under these conditions. The obtained results are in qualitative agreement with the theory of cascade capture of carriers on isolated centers in crossed electric and magnetic fields.

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44

Cruz, M. B., E. R. Bezerra de Mello y A. Yu Petrov. "Thermal corrections to the Casimir energy in a Lorentz-breaking scalar field theory". Modern Physics Letters A 33, n.º 20 (28 de junio de 2018): 1850115. http://dx.doi.org/10.1142/s0217732318501158.

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In this paper, we investigate the thermal effect on the Casimir energy associated with a massive scalar quantum field confined between two large parallel plates in a CPT-even, aether-like Lorentz-breaking scalar field theory. In order to do that, we consider a nonzero chemical potential for the scalar field assumed to be in thermal equilibrium at some finite temperature. The calculations of the energies are developed by using the Abel–Plana summation formula, and the corresponding results are analyzed in several asymptotic regimes of the parameters of the system, like mass, separations between the plates and temperature.

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45

Jun-Chen, Su y Zheng Fu-Hou. "Correct Path-Integral Formulation of Quantum Thermal Field Theory in Coherent State Representation". Communications in Theoretical Physics 43, n.º 4 (abril de 2005): 641–56. http://dx.doi.org/10.1088/0253-6102/43/4/016.

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46

FAN, HONGYI y HUI WANG. "QUANTUM FLUCTUATION OF TWO-MODE SQUEEZED THERMAL VACUUM STATES AND THE THERMAL WIGNER OPERATOR STUDIED BY VIRTUE OF <η| REPRESENTATION". Modern Physics Letters B 15, n.º 12n13 (10 de junio de 2001): 397–406. http://dx.doi.org/10.1142/s0217984901001872.

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Based on the <η| representation in Thermo Field Dynamics3 we introduce the thermal Wigner operator, with which we reach the conclusion that due to the thermal effect the quantum fluctuation of two-mode squeezed vacuum state increases by a factor cosh 2θ, where tanh θ = exp (-ℏω/2kT). We also mathematically analyse the formalism of Thermo Field Dynamics in the context of entanglement theory.

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47

FEDELE, RENATO, FATEMA TANJIA, SERGIO DE NICOLA y DUŠAN JOVANOVIĆ. "The plasma wake field excitation: Recent developments from thermal to quantum regime". Journal of Plasma Physics 79, n.º 6 (diciembre de 2013): 1095–98. http://dx.doi.org/10.1017/s0022377813001293.

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AbstractTo describe the transverse nonlinear and collective self-consistent interaction of a long relativistic electron or positron beam with an unmagnetized plasma, a pair of coupled nonlinear differential equations were proposed by Fedele and Shukla in 1992 (Fedele, R. and Shukla, P. K. 1992a Phys. Rev. A 45, 4045). They were obtained within the quantum-like description provided by the thermal wave model and the theory of plasma wake field excitation. The pair of equations comprises a 2D Schrödinger-like equation for a complex wave function (whose squared modulus is proportional to beam density) and a Poisson-like equation for the plasma wake potential. The dispersion coefficient of the Schrödinger-like equation is proportional to the beam thermal emittance. More recently, Fedele–Shukla equations have been further applied to magnetized plasmas, and solutions were found in the form of nonlinear vortex states and ring solitons. They have been also applied to plasma focusing problems and extended from thermal to quantum regimes. We present here a review of the original approach, and subsequent developments.

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48

SURESH, P. K. "THERMAL SQUEEZING AND DENSITY FLUCTUATIONS IN SEMICLASSICAL THEORY OF GRAVITY". Modern Physics Letters A 16, n.º 11 (10 de abril de 2001): 707–17. http://dx.doi.org/10.1142/s0217732301003802.

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A thermal squeezed state representation is constructed for each mode of a quantized scalar field in a spatially homogeneous and flat Robertson–Walker metric and the validity of semiclassical Einstein equation by analyzing the density fluctuation is examined. The density fluctuation in thermal squeezed state is very large and therefore the semiclassical theory may not be valid for squeezing parameter more than unity, however the theory holds when the associated squeezing parameter is much less than the unity. Further noted that the semiclassical theory is consistent in thermal coherent state formalism. The present study can account for the density fluctuations due to the thermal and quantum effects in semiclassical theory of gravity.

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49

Srinivasan, K., L. Sriramkumar y T. Padmanabhan. "Possible Quantum Interpretation of Certain Power Spectra in Classical Field Theory". International Journal of Modern Physics D 06, n.º 05 (octubre de 1997): 607–23. http://dx.doi.org/10.1142/s0218271897000376.

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In this paper we report an analogue for the vacuum state in classical field theory and its Planckian nature with respect to uniformly accelerated observers. When a real, monochromatic, mode of a scalar field is Fourier analyzed with respect to the proper time of a uniformly accelerating observer, the resulting power spectrum consists of three terms none of which have a simple classical meaning. Specifically, the three terms are (i) a factor (1/2) that is typical of the ground state energy of a quantum ascillator, (ii) a Planckian distribution N(Ω) and — most importantly — (iii) a term [Formula: see text], which is the root mean aquare fluctuations about the Planckian distribution. It is the appearance of the root mean square fluctuations that motivates us to attribute a "thermal" nature to the power spectrum. Such a power spectrum also arises when we Fourier analyze a real, monochromatic, plane electromagnetic wave in the frame of a uniformly accelerating observer. We also present a model of a detector whose response is the Fourier spectrum of the field with respect to its proper time, which illustrates that it should, in principle, be possible to physically measure the power spectrum we have obtained. These results show that some of the "purely" quantum mechanical results might have a classical analogue.

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50

Holovatch, Yu, C. von Ferber y Yu Honchar. "DNA thermal denaturation by polymer field theory approach: effects of the environment". Condensed Matter Physics 24, n.º 3 (2021): 33603. http://dx.doi.org/10.5488/cmp.24.33603.

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We analyse the effects of the environment (solvent quality, presence of extended structures - crowded environment) that may have impact on the order of the transition between denaturated and bounded DNA states and lead to changes in the scaling laws that govern conformational properties of DNA strands. We find that the effects studied significantly influence the strength of the first order transition. To this end, we re-consider the Poland-Scheraga model and apply a polymer field theory to calculate entropic exponents associated with the denaturated loop distribution. For the d = 3 case, the corresponding diverging ε = 4-d expansions are evaluated by restoring their convergence via the resummation technique. For the space dimension d = 2, the exponents are deduced from mapping the polymer model onto a two-dimensional random lattice, i.e., in the presence of quantum gravity. We also show that the first order transition is further strengthened by the presence of extended impenetrable regions in a solvent that restrict the number of the macromolecule configurations.

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