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Journal articles on the topic 'Spacetime Structure'

Author: Grafiati

Published: 2 June 2025

Last updated: 31 July 2025

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1

Konkowski, Deborah A., and Thomas M. Helliwell. "Understanding singularities — Classical and quantum." International Journal of Modern Physics A 31, no. 02n03 (2016): 1641007. http://dx.doi.org/10.1142/s0217751x16410074.

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The definitions of classical and quantum singularities are reviewed. Examples are given of both as well as their utility in general relativity. In particular, the classical and quantum singularity structure of certain interesting conformally static spherically symmetric spacetimes modeling scalar field collapse are reviewed. The spacetimes include the Roberts spacetime, the Husain-Martinez-Nuñez spacetime and the Fonarev spacetime. The importance of understanding spacetime singularity structure is discussed.

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2

Duggal, K. L. "Space time manifolds and contact structures." International Journal of Mathematics and Mathematical Sciences 13, no. 3 (1990): 545–53. http://dx.doi.org/10.1155/s0161171290000783.

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A new class of contact manifolds (carring a global non-vanishing timelike vector field) is introduced to establish a relation between spacetime manifolds and contact structures. We show that odd dimensional strongly causal (in particular, globally hyperbolic) spacetimes can carry a regular contact structure. As examples, we present a causal spacetime with a non regular contact structure and a physical model [Gödel Universe] of Homogeneous contact manifold. Finally, we construct a model of 4-dimensional spacetime of general relativity as a contact CR-submanifold.

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3

KRÓL, JERZY. "TOPOS THEORY AND SPACETIME STRUCTURE." International Journal of Geometric Methods in Modern Physics 04, no. 02 (2007): 297–303. http://dx.doi.org/10.1142/s0219887807002028.

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According to the recently proposed model of spacetime, various difficulties of quantum field theories and semiclassical quantum gravity on curved 4-Minkowski spacetimes gain new formulations, leading to new solutions. The quantum mechanical effects appear naturally when diffeomorphisms are lifted to 2-morphisms between topoi. The functional measures can be well defined. Diffeomorphisms invariance and background independence are approached from the perspective of topoi. In the spacetimes modified at short distances by the internal structure of some topoi, the higher dimensional regions appear a

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4

Suh, Young, Pradip Majhi, and De Chand. "On mixed quasi-Einstein spacetimes." Filomat 32, no. 8 (2018): 2707–19. http://dx.doi.org/10.2298/fil1808707s.

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The object of the present paper is to study mixed quasi-Einstein spacetimes, briefly M(QE)4 spacetimes. First we prove that every Z Ricci pseudosymmetric M(QE)4 spacetimes is a Z Ricci semisymmetric spacetime. Then we study Z flat spacetimes. Also we consider Ricci symmetric M(QE)4 spacetimes and among others we prove that the local cosmological structure of a Ricci symmetricM(QE)4 perfect fluid spacetime can be identified as Petrov type I, DorO. We show that such a spacetime is the Robertson-Walker spacetime. Moreover we deal with mixed quasi-Einstein spacetimes with the associated generators

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5

Khan, Amir Sultan, Israr Ali Khan, Saeed Islam, and Farhad Ali. "Noether symmetry analysis for novel gravitational wave-like spacetimes and their conservation laws." Modern Physics Letters A 35, no. 28 (2020): 2050234. http://dx.doi.org/10.1142/s021773232050234x.

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The phenomena-like Hawking radiation, the collapse of black holes, and neutron stars decrease the curvature of spacetime continuously with the passage of time. The time conformal factor adds some curvature to nonstatic spacetime. In this article, some novel classes of nonstatic plane-symmetric spacetimes are explored by introducing a time conformal factor in the exact plane-symmetric spacetimes in such a way that their symmetric structure remains conserved. This technique re-scales the energy contents of the corresponding spacetimes, which comes with a re-scaled part in each spacetime. The inv

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6

Barrett, Thomas William. "Spacetime structure." Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics 51 (August 2015): 37–43. http://dx.doi.org/10.1016/j.shpsb.2015.06.004.

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7

De, Avik, and Pradip Majhi. "Weakly Ricci symmetric spacetimes." International Journal of Geometric Methods in Modern Physics 15, no. 01 (2017): 1850007. http://dx.doi.org/10.1142/s021988781850007x.

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The objective of the present paper is to study weakly Ricci symmetric spacetimes. Among others, we prove that a weakly Ricci symmetric spacetime obeying Einstein’s field equation without cosmological constant represents stiff matter. Moreover, it is shown that the local cosmological structure of a weakly Ricci symmetric perfect fluid spacetime can be identified as Petrov type [Formula: see text], [Formula: see text] or [Formula: see text]. Next, we prove that a dust and dark fluid weakly Ricci symmetric spacetime satisfying Einstein’s field equation without cosmological constant is vacuum. Fin

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8

Mallick, Sahanous, and Uday Chand De. "Spacetimes admitting W2-curvature tensor." International Journal of Geometric Methods in Modern Physics 11, no. 04 (2014): 1450030. http://dx.doi.org/10.1142/s0219887814500303.

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The object of this paper is to study spacetimes admitting W2-curvature tensor. At first we prove that a W2-flat spacetime is conformally flat and hence it is of Petrov type O. Next, we prove that if the perfect fluid spacetime with vanishing W2-curvature tensor obeys Einstein's field equation without cosmological constant, then the spacetime has vanishing acceleration vector and expansion scalar and the perfect fluid always behaves as a cosmological constant. It is also shown that in a perfect fluid spacetime of constant scalar curvature with divergence-free W2-curvature tensor, the energy-mom

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9

Boucetta, Mohamed, Aissa Meliani, and Abdelghani Zeghib. "Kundt three-dimensional left invariant spacetimes." Journal of Mathematical Physics 63, no. 11 (2022): 112501. http://dx.doi.org/10.1063/5.0091202.

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Kundt spacetimes are of great importance to general relativity. We show that a Kundt spacetime is a Lorentz manifold with a non-singular isotropic geodesic vector field having its orthogonal distribution integrable and determining a totally geodesic foliation. We give the local structure of Kundt spacetimes and some properties of left invariant Kundt structures on Lie groups. Finally, we classify all left invariant Kundt structures on three-dimensional simply connected unimodular Lie groups.

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10

Seidel, Paola Terezinha, and Luís Antonio Cabral. "Dualities and geometrical invariants for static and spherically symmetric spacetimes." International Journal of Modern Physics D 25, no. 09 (2016): 1641007. http://dx.doi.org/10.1142/s0218271816410078.

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In this work, we consider spinless particles in curved spacetime and symmetries related to extended isometries. We search for solutions of a generalized Killing equation whose structure entails a general class of Killing tensors. The conserved quantities along particle’s geodesic are associated with a dual description of the spacetime metric. In the Hamiltonian formalism, some conserved quantities generate a dual description of the metric. The Killing tensors belonging to the conserved objects imply in a nontrivial class of dual metrics even for a Schwarzschild metric in the original spacetime

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11

DA ROCHA, ROLDÃO, J. M. HOFF DA SILVA, and ALEX E. BERNARDINI. "ELKO SPINOR FIELDS AS A TOOL FOR PROBING EXOTIC TOPOLOGICAL SPACETIME FEATURES." International Journal of Modern Physics: Conference Series 03 (January 2011): 133–42. http://dx.doi.org/10.1142/s201019451100122x.

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We report about some achievements and developments provided by the ELKO program, in particular the ones recently accomplished.1 Exotic dark spinor fields has been investigated in the context of inequivalent spin structures on arbitrary curved spacetimes, which induces an additional term on the associated Dirac operator, related to a Čech cohomology class. Exotic terms operating on standard model Dirac spinor fields are usually absorbed by gauge transformations encoded as a shift of some vector potential representing an element of the cohomology group H1(M, ℤ2). That is not the case of ELKO, on

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12

Franco, Nicolas. "Physical models from noncommutative causality." EPJ Web of Conferences 182 (2018): 02043. http://dx.doi.org/10.1051/epjconf/201818202043.

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We introduced few years ago a new notion of causality for noncommutative spacetimes directly related to the Dirac operator and the concept of Lorentzian spectral triple. In this paper, we review in a non-technical way the noncommutative causal structure of many toy models as almost commutative spacetimes and the Moyal-Weyl spacetime. We show that those models present some unexpected physical interpretations as a geometrical explanation of the Zitterbewegung trembling motion of a fermion as well as some geometrical constraints on translations and energy jumps of wave packets on the Moyal spacet

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13

Delaporte, Héloïse, and Astrid Eichhorn. "The principled-parameterized approach to gravitational collapse." Journal of Cosmology and Astroparticle Physics 2025, no. 03 (2025): 074. https://doi.org/10.1088/1475-7516/2025/03/074.

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Abstract New physics beyond General Relativity impacts black-hole spacetimes. The effects of new physics can be investigated in a largely theory-agnostic way by following the principled-parameterized approach. In this approach, a classical black-hole metric is upgraded by following a set of principles, such as regularity, i.e., the absence of curvature singularities. We expect these principles to hold in many theories beyond General Relativity. In the present paper, we implement this approach for time-dependent spacetimes describing gravitational collapse. We find that the Vaidya spacetime bec

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14

Schleich, K., and D. M. Witt. "Designer de Sitter spacetimes." Canadian Journal of Physics 86, no. 4 (2008): 591–95. http://dx.doi.org/10.1139/p07-191.

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Recent observations in cosmology indicate an accelerating expansion of the Universe postulated to arise from some form of dark energy, the paradigm being positive cosmological constant. De Sitter spacetime is the well-known isotropic solution to the Einstein equations with cosmological constant. However, as discussed here, it is not the most general, locally isotropic solution. One can construct an infinite family of such solutions, designer de Sitter spacetimes, which are everywhere locally isometric to a region of de Sitter spacetime. However, the global dynamics of these designer cosmologie

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15

Minguzzi, Ettore. "Destructuring Physics: A functional derivation of spacetime." Journal of Physics: Conference Series 3017, no. 1 (2025): 012004. https://doi.org/10.1088/1742-6596/3017/1/012004.

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Abstract I propose that Physics should be formulated using minimal mathematical structure, beginning with its foundational arena: spacetime. This paper opens with a concise overview of several research directions explored in previous work. Among these are the proposal to represent spacetime at the quantum scale using (measure) closed ordered spaces; the unification of causality and topology through quasi-uniformities; the concept of the product trick to unify causality and metricity; the introduction of upper semi-continuous (stable) Lorentzian distances; the representation of spacetime via st

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16

Kumar, Jitendra, Shafqat Ul Islam, and Sushant G. Ghosh. "Loop Quantum Gravity motivated multihorizon rotating black holes." Journal of Cosmology and Astroparticle Physics 2022, no. 11 (2022): 032. http://dx.doi.org/10.1088/1475-7516/2022/11/032.

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Abstract With a semiclassical polymerization in the loop quantum gravity (LQG), the interior of the Schwarzschild black holes provides a captivating single-horizon regular black hole spacetime. The shortage of rotating black hole models in loop quantum gravity (LQG) substantially restrains the progress of testing LQG from observations. Motivated by this, starting with a spherical LQG black hole as a seed metric, we construct a rotating spacetime using the revised Newman-Janis algorithm, namely, the LQG-motivated rotating black holes (LMRBH), which encompasses Kerr (l = 0) black holes as an exc

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17

Kabel, Viktoria, Anne-Catherine de la Hamette, Esteban Castro-Ruiz, and Časlav Brukner. "Quantum conformal symmetries for spacetimes in superposition." Quantum 8 (December 4, 2024): 1547. https://doi.org/10.22331/q-2024-12-04-1547.

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Without a complete theory of quantum gravity, the question of how quantum fields and quantum particles behave in a superposition of spacetimes seems beyond the reach of theoretical and experimental investigations. Here we use an extension of the quantum reference frame formalism to address this question for the Klein-Gordon field residing on a superposition of conformally equivalent metrics. Based on the group structure of “quantum conformal transformations&apos;&apos;, we construct an explicit quantum operator that can map states describing a quantum field on a superposition of spacet

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18

WANAS, M. I., and SAMAH A. AMMAR. "SPACETIME STRUCTURE AND ELECTROMAGNETISM." Modern Physics Letters A 25, no. 20 (2010): 1705–21. http://dx.doi.org/10.1142/s0217732310032883.

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Two Lagrangian functions are used to construct geometric field theories. One of these Lagrangians depends on the curvature of space, while the other depends on curvature and torsion. It is shown that the theory constructed from the first Lagrangian gives rise to pure gravity, while the theory constructed using the second Lagrangian gives rise to both gravity and electromagnetism. The two theories are constructed in a version of absolute parallelism geometry in which both curvature and torsion are, simultaneously, nonvanishing. One single geometric object, W-tensor, reflecting the properties of

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19

Bernar, Rafael P., Luís C. B. Crispino, and Atsushi Higuchi. "Circular geodesic radiation in Schwarzschild spacetime: A semiclassical approach." International Journal of Modern Physics D 27, no. 11 (2018): 1843002. http://dx.doi.org/10.1142/s0218271818430022.

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Extreme curvature settings and nontrivial causal structure of curved spacetimes may have interesting theoretical and practical implications for quantum field theories. Radiation emission in black hole spacetimes is one such scenario in which the semiclassical approach, i.e. quantum fields propagating in a nondynamical background spacetime, adds a very simple conceptual point of view and allows us to compute the emitted power in a straightforward way. Within this context, we reexamine sources in circular orbit around a Schwarzschild black hole, investigating the emission of scalar, electromagne

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20

Crispim, T. M., Marcos V. de S. Silva, G. Alencar, Celio R. Muniz, and Diego Sáez-Chillón Gómez. "Field sources for wormholes with multiple throats/anti-throats." Classical and Quantum Gravity 42, no. 8 (2025): 085005. https://doi.org/10.1088/1361-6382/adc654.

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Abstract In this work, we investigate wormhole geometries with multiple throats and anti-throats in general relativity. The existence of these structures is identified through the analysis of minima and maxima in the area of the solution. Using embedding diagrams, we visualize the geometry and demonstrate that these objects exhibit a complex structure, distinct from standard single-throat wormholes. We further analyze the geodesic motion in such spacetimes. The solutions are derived from Einstein’s equations by coupling a phantom scalar field to nonlinear electrodynamics, and we show that dist

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21

Romero, Juan M., and J. David Vergara. "Lifshitz field theories, Snyder noncommutative spacetime and momentum-dependent metric." Modern Physics Letters A 30, no. 29 (2015): 1550155. http://dx.doi.org/10.1142/s0217732315501552.

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In this paper, we propose three different modified relativistic particles. In the first case, we propose a particle with metrics depending on the momenta and we show that the quantum version of these systems includes different field theories, as Lifshitz field theories. As a second case, we propose a particle that implies a modified symplectic structure and we show that the quantum version of this system gives different noncommutative spacetimes, for example the Snyder spacetime. In the third case, we combine both structures before mentioned, namely noncommutative spacetimes and momentum-depen

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22

CAMCI, UGUR. "DIRAC ANALYSIS AND INTEGRABILITY OF GEODESIC EQUATIONS FOR CYLINDRICALLY SYMMETRIC SPACETIMES." International Journal of Modern Physics D 12, no. 08 (2003): 1431–44. http://dx.doi.org/10.1142/s0218271803003621.

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Dirac's constraint analysis and the symplectic structure of geodesic equations are obtained for the general cylindrically symmetric stationary spacetime. For this metric, using the obtained first order Lagrangian, the geodesic equations of motion are integrated, and found some solutions for Lewis, Levi-Civita, and Van Stockum spacetimes.

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23

Triantafyllopoulos, Alkiviadis, Emmanuel Kapsabelis, and Panayiotis C. Stavrinos. "Raychaudhuri Equations, Tidal Forces, and the Weak-Field Limit in Schwarzshild–Finsler–Randers Spacetime." Universe 10, no. 1 (2024): 26. http://dx.doi.org/10.3390/universe10010026.

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In this article, we study the form of the deviation of geodesics (tidal forces) and the Raychaudhuri equation in a Schwarzschild–Finsler–Randers (SFR) spacetime which has been investigated in previous papers. This model is obtained by considering the structure of a Lorentz tangent bundle of spacetime and, in particular, the kind of the curvatures in generalized metric spaces where there is more than one curvature tensor, such as Finsler-like spacetimes. In these cases, the concept of the Raychaudhuri equation is extended with extra terms and degrees of freedom from the dependence on internal v

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24

Stoica, O. C. "Spacetime Causal Structure and Dimension from Horismotic Relation." Journal of Gravity 2016 (May 25, 2016): 1–6. http://dx.doi.org/10.1155/2016/6151726.

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A reflexive relation on a set can be a starting point in defining the causal structure of a spacetime in General Relativity and other relativistic theories of gravity. If we identify this relation as the relation between lightlike separated events (the horismos relation), we can construct in a natural way the entire causal structure: causal and chronological relations, causal curves, and a topology. By imposing a simple additional condition, the structure gains a definite number of dimensions. This construction works with both continuous and discrete spacetimes. The dimensionality is obtained

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25

Gómez, Jose, and Douglas Engholm. "Natural constants as properties of the Spacetime structure. A geometrical and mathematical design." Revista de Investigación de Física 26, no. 2 (2023): 63–86. http://dx.doi.org/10.15381/rif.v26i2.23654.

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In current physics there are two Natural constants with meanings that remain unresolved: the Cosmological and the Fine Structure constants. Both are related to the theory of relativity and quantum mechanics. Here we attempt to give meaning to each of these constants and the relationship that can exist between them by proposing a new system of units based on Spacetime Structure. We will extend this new concept to unsolved questions in physics and cosmology, as well as describing the process by which the Spacetime Structure premises were developed to provide a basis for our thesis that Spacetime

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26

Claude, Gauthier &. Pierre Gravel. "Spacetimes with Polycrystalline Symmetry." MATHEMATICS EDUCATION LV, no. 1 (2021): 1–11. https://doi.org/10.5281/zenodo.5790968.

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We find the conditions imposed on the metric of a spacetime by requiring that its spacelike hypersurfaces possess, at a given scale, more than one Euclidean crystalline symmetry. Such spacetimes gather into four classes. We show that three of these classes correspond to spacetimes without physical meaning. It follows that no material object can be created with the perfect crystalline structure belonging to these three classes. This result implies contradictions between general relativity and crystallography.

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27

Brightwell, Graham, and Ruth Gregory. "Structure of random discrete spacetime." Physical Review Letters 66, no. 3 (1991): 260–63. http://dx.doi.org/10.1103/physrevlett.66.260.

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28

McKIE, JOHNR. "Conventionalism, realism, and spacetime structure." Theoria 54, no. 2 (2008): 81–101. http://dx.doi.org/10.1111/j.1755-2567.1988.tb00713.x.

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29

Barrett, Thomas William, and J. B. Manchak. "On Coordinates and Spacetime Structure." Philosophy of Physics 2, no. 1 (2024): 11. http://dx.doi.org/10.31389/pop.131.

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Philosophers and physicists often claim that the “privileged coordinates” of a physical theory provide a window into its structure. The purpose of this paper is to examine whether this is the case. We show that there are general relativistic spacetimes that admit the same privileged coordinates but have different structure, and we infer from this that privileged coordinates do not provide a perfect guide to underlying structure. We conclude by isolating the conditions under which privileged coordinates do perfectly reflect structure.

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30

Ni, Wei-Tou. "On spacetime structure and electrodynamics." International Journal of Modern Physics D 25, no. 11 (2016): 1603001. http://dx.doi.org/10.1142/s0218271816030012.

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Electrodynamics is the most tested fundamental physical theory. Relativity arose from the completion of Maxwell–Lorentz electrodynamics. Introducing the metric [Formula: see text] as gravitational potential in 1913, versed in general (coordinate-)covariant formalism in 1914 and shortly after the completion of general relativity, Einstein put the Maxwell equations in general covariant form with only the constitutive relation between the excitation and the field dependent on and connected by the metric in 1916. Further clarification and developments by Weyl in 1918, Murnaghan in 1921, Kottler in

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31

Kirchbach, M., and D. V. Ahluwalia. "Spacetime structure of massive gravitino." Physics Letters B 529, no. 1-2 (2002): 124–31. http://dx.doi.org/10.1016/s0370-2693(02)01237-6.

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32

Brandt, Howard E. "Structure of spacetime tangent bundle." Foundations of Physics Letters 4, no. 6 (1991): 523–36. http://dx.doi.org/10.1007/bf00689889.

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33

Szab�, L�szl� E. "Spacetime structure on quantum lattice." International Journal of Theoretical Physics 31, no. 9 (1992): 1803–10. http://dx.doi.org/10.1007/bf00671788.

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ZHOU, SHENG, JUHUA CHEN, and YONGJIU WANG. "GEODESIC STRUCTURE OF TEST PARTICLE IN BARDEEN SPACETIME." International Journal of Modern Physics D 21, no. 09 (2012): 1250077. http://dx.doi.org/10.1142/s0218271812500770.

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The Bardeen model describes a regular spacetime, i.e. a singularity-free black hole spacetime. In this paper, by analyzing the behavior of the effective potential for the particles and photons, we investigate the timelike and null geodesic structures in the Bardeen spacetime. At the same time, all kinds of orbits, which are allowed according to the energy level corresponding to the effective potentials, are numerically simulated in detail. We find many-world bound orbits, two-world escape orbits and escape orbits in this spacetime. We also find that bound orbits precession directions are oppos

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CALCAGNI, GIANLUCA. "MULTIFRACTIONAL SPACETIMES, ASYMPTOTIC SAFETY AND HOŘAVA–LIFSHITZ GRAVITY." International Journal of Modern Physics A 28, no. 19 (2013): 1350092. http://dx.doi.org/10.1142/s0217751x13500929.

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We compare the recently formulated multifractional spacetimes with field theories of quantum gravity based on the renormalization group (RG), such as asymptotic safety and Hořava–Lifshitz gravity. The change of spacetime dimensionality with the probed scale is realized in both cases by an adaptation of the measurement tools ("rods") to the scale, but in different ways. In the multifractional case, by an adaptation of the position-space measure, which can be encoded into an explicit scale dependence of effective coordinates. In the case of RG-based theories, by an adaptation of the momenta. The

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Zhang, Lu, Songbai Chen, and Jiliang Jing. "Gravitational lensing by a black hole with torsion." International Journal of Modern Physics D 27, no. 12 (2018): 1850110. http://dx.doi.org/10.1142/s0218271818501109.

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In this paper, we have investigated the gravitational lensing in a spherically symmetric spacetime with torsion in the generalized Einstein–Cartan–Kibble–Sciama (ECKS) theory of gravity by considering higher order terms. The torsion parameters change the spacetime structure, which affects the photon sphere, the deflection angle and the strong gravitational lensing. The condition of existence of horizons is not inconsistent with that of the photon sphere. Especially, there exists a novel case in which there is horizon but no photon sphere for the considered spacetime. In this special case, the

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Henderson, Laura J., Su Yu Ding, and Robert B. Mann. "Entanglement harvesting with a twist." AVS Quantum Science 4, no. 1 (2022): 014402. http://dx.doi.org/10.1116/5.0078314.

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One consequence of the cosmic censorship conjecture is that any topological structure will ultimately collapse to within the horizons of a set of black holes, and as a result, an external classical observer will be unable to probe it. However, a single two-level quantum system [Unruh–DeWitt (UDW) detector] that remains outside of the horizon has been shown to distinguish between a black hole and its associated geon counterpart via its different response rates. Here, we extend this investigation of the quantum vacuum outside of an [Formula: see text] geon by considering the entanglement structu

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YANG, HYUN SEOK. "EMERGENT GEOMETRY AND QUANTUM GRAVITY." Modern Physics Letters A 25, no. 28 (2010): 2381–97. http://dx.doi.org/10.1142/s0217732310034067.

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We explain how quantum gravity can be defined by quantizing spacetime itself. A pinpoint is that the gravitational constant [Formula: see text] whose physical dimension is of (length)2 in natural unit introduces a symplectic structure of spacetime which causes a noncommutative spacetime at the Planck scale L P . The symplectic structure of spacetime M leads to an isomorphism between symplectic geometry (M, ω) and Riemannian geometry (M, g) where the deformations of symplectic structure ω in terms of electromagnetic fields F = dA are transformed into those of Riemannian metric g. This approach

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NG, Y. JACK. "SPACETIME FOAM." International Journal of Modern Physics D 11, no. 10 (2002): 1585–90. http://dx.doi.org/10.1142/s0218271802002931.

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Spacetime is composed of a fluctuating arrangement of bubbles or loops called spacetime foam, or quantum foam. We use the holographic principle to deduce its structure, and show that the result is consistent with gedanken experiments involving spacetime measurements. We propose to use laser-based atom interferometry techniques to look for spacetime fluctuations. Our analysis makes it clear that the physics of quantum foam is inextricably linked to that of black holes. A negative experimental result, therefore, might have non-trivial ramifications for semiclassical gravity and black hole physic

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Fewster, Christopher J. "The art of the state." International Journal of Modern Physics D 27, no. 11 (2018): 1843007. http://dx.doi.org/10.1142/s0218271818430071.

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Quantum field theory (QFT) on curved spacetimes lacks an obvious distinguished vacuum state. We review a recent no-go theorem that establishes the impossibility of finding a preferred state in each globally hyperbolic spacetime, subject to certain natural conditions. The result applies in particular to the free scalar field, but the proof is model-independent and therefore of wider applicability. In addition, we critically examine the recently proposed “SJ states”, that are determined by the spacetime geometry alone, but which fail to be Hadamard in general. We describe a modified construction

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41

Siddiqi, Mohd Danish, Fatemah Mofarreh, Aliya Naaz Siddiqui, and Shah Alam Siddiqui. "Geometrical Structure in a Relativistic Thermodynamical Fluid Spacetime." Axioms 12, no. 2 (2023): 138. http://dx.doi.org/10.3390/axioms12020138.

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The goal of the present research paper is to study how a spacetime manifold evolves when thermal flux, thermal energy density and thermal stress are involved; such spacetime is called a thermodynamical fluid spacetime (TFS). We deal with some geometrical characteristics of TFS and obtain the value of cosmological constant Λ. The next step is to demonstrate that a relativistic TFS is a generalized Ricci recurrent TFS. Moreover, we use TFS with thermodynamic matter tensors of Codazzi type and Ricci cyclic type. In addition, we discover the solitonic significance of TFS in terms of the Ricci metr

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42

Le Bihan, Baptiste. "Priority Monism Beyond Spacetime." Metaphysica 19, no. 1 (2018): 95–111. http://dx.doi.org/10.1515/mp-2018-0005.

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AbstractI will defend two claims. First, Schaffer’s priority monism is in tension with many research programs in quantum gravity. Second, priority monism can be modified into a view more amenable to this physics. The first claim is grounded in the fact that promising approaches to quantum gravity such as loop quantum gravity or string theory deny the fundamental reality of spacetime. Since fundamental spacetime plays an important role in Schaffer’s priority monism by being identified with the fundamental structure, namely the cosmos, the disappearance of spacetime in these views might undermin

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Baron, Sam, and Baptiste Le Bihan. "Composing Spacetime." Journal of Philosophy 119, no. 1 (2022): 33–54. http://dx.doi.org/10.5840/jphil202211912.

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According to a number of approaches in theoretical physics, spacetime does not exist fundamentally. Rather, spacetime exists by depending on another, more fundamental, non-spatiotemporal structure. A prevalent opinion in the literature is that this dependence should not be analyzed in terms of composition. We should not say, that is, that spacetime depends on an ontology of non-spatiotemporal entities in virtue of having them as parts. But is that really right? On the contrary, we argue that a mereological approach to dependent spacetime is not only viable, but promises to enhance our understa

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Kothawala, Dawood. "Small-scale structure of spacetime and its implications." International Journal of Modern Physics D 28, no. 06 (2019): 1950079. http://dx.doi.org/10.1142/s0218271819500792.

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If there exists a lower bound [Formula: see text] to spacetime intervals which is Lorentz-invariant, then the effective description of spacetime that incorporates such a lower bound must necessarily be nonlocal. Such a nonlocal description can be derived using standard tools of differential geometry, but using as basic variables certain bi-tensors instead of the conventional metric tensor [Formula: see text]. This allows one to construct a qmetric [Formula: see text], using the Synge’s world function [Formula: see text] and the van Vleck determinant [Formula: see text], that incorporates the l

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Eichhorn, Astrid, Aaron Held, and Philipp-Vincent Johannsen. "Universal signatures of singularity-resolving physics in photon rings of black holes and horizonless objects." Journal of Cosmology and Astroparticle Physics 2023, no. 01 (2023): 043. http://dx.doi.org/10.1088/1475-7516/2023/01/043.

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Abstract Within quantum-gravity approaches and beyond, different mechanisms for singularity resolution in black holes exist. Under a set of assumptions that we spell out in detail, these mechanisms leave their imprint in shadow images of spherically symmetric black holes. We find that even current EHT accuracy is sufficient to place nontrivial constraints on the scale of new physics within one modified spacetime, if the EHT measurement of M87* is combined with an independent measurement of the black-hole mass. In other spacetimes, increased accuracy is required that the next-generation EHT may

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KIM, SANG PYO. "PROBING THE VACUUM STRUCTURE OF SPACETIME." International Journal of Modern Physics: Conference Series 12 (January 2012): 310–19. http://dx.doi.org/10.1142/s2010194512006514.

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We explore the question of how to probe the vacuum structure of space time by a massive scalar field through interaction with background gravitons. Using the Γ-regularization for the in-/out-state formalism, we find the effective action of a scalar field in a conformally, asymptotically flat spacetime and a four-dimensional de Sitter space, which is a gravitational analog of the Heisenberg-Euler and Schwinger effective action for a charged scalar in a constant electric field. The effective action is nonperturbative in that it sums all one-loop diagrams with arbitrary number of external lines o

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Dolan, B. P., Kumar S. Gupta, and A. Stern. "Noncommutativity and quantum structure of spacetime." Journal of Physics: Conference Series 174 (June 1, 2009): 012023. http://dx.doi.org/10.1088/1742-6596/174/1/012023.

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Gregory, Ruth, and Caroline Santos. "Spacetime structure of the global vortex." Classical and Quantum Gravity 20, no. 1 (2002): 21–35. http://dx.doi.org/10.1088/0264-9381/20/1/302.

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Curiel, Erik. "On the Existence of Spacetime Structure." British Journal for the Philosophy of Science 69, no. 2 (2018): 447–83. http://dx.doi.org/10.1093/bjps/axw014.

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Marlow, A. R. "Quantum theoretical origin of spacetime structure." International Journal of Theoretical Physics 25, no. 5 (1986): 561–71. http://dx.doi.org/10.1007/bf00668790.

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