scholarly journals AN ISOTROPIZATION MECHANISM IN BIANCHI I MODEL

2003 ◽  
Vol 12 (08) ◽  
pp. 1499-1508
Author(s):  
H. H. FLICHE ◽  
R. TRIAY ◽  
M. NOVELLO ◽  
L. R. De FREITAS
Keyword(s):  
Initial Conditions ◽  
Hamiltonian Formalism ◽  
Anisotropic Pressure ◽  
Energy Tensor ◽  
Stress Energy Tensor ◽  
Stress Energy ◽  
Elimination Mechanism ◽  
Pass Through ◽  
The Universe ◽  
Efficient Elimination

We ask whether the problem on the initial conditions in Cosmology can be solved if an efficient elimination mechanism of the anisotropy was present at earlier epochs. We explore the consequences of the existence of an epoch in which the material content of the Universe was represented by an stress-energy tensor possessing anisotropic pressure which depends nonlinearly on the expansion parameter. We show that for selected candidate behaviors the associated shear pass through a maximum and vanishes asymptotically. We use the Hamiltonian formalism to define a constant of motion which enables us to classify the cosmological world-models.

scholarly journals Existence and Uniqueness of Solutions of the Semiclassical Einstein Equation in Cosmological Models

2021 ◽  
Author(s):  
Paolo Meda ◽  
Nicola Pinamonti ◽  
Daniel Siemssen
Keyword(s):  
Einstein Equation ◽  
Existence And Uniqueness ◽  
Inversion Formula ◽  
Initial Conditions ◽  
Energy Tensor ◽  
Stress Energy Tensor ◽  
Expectation Values ◽  
Uniqueness Of Solutions ◽  
Stress Energy ◽  
Non Local

AbstractWe prove existence and uniqueness of solutions of the semiclassical Einstein equation in flat cosmological spacetimes driven by a quantum massive scalar field with arbitrary coupling to the scalar curvature. In the semiclassical approximation, the backreaction of matter to curvature is taken into account by equating the Einstein tensor to the expectation values of the stress-energy tensor in a suitable state. We impose initial conditions for the scale factor at finite time, and we show that a regular state for the quantum matter compatible with these initial conditions can be chosen. Contributions with derivative of the coefficient of the metric higher than the second are present in the expectation values of the stress-energy tensor and the term with the highest derivative appears in a non-local form. This fact forbids a direct analysis of the semiclassical equation, and in particular, standard recursive approaches to approximate the solution fail to converge. In this paper, we show that, after partial integration of the semiclassical Einstein equation in cosmology, the non-local highest derivative appears in the expectation values of the stress-energy tensor through the application of a linear unbounded operator which does not depend on the details of the chosen state. We prove that an inversion formula for this operator can be found, furthermore, the inverse happens to be more regular than the direct operator and it has the form of a retarded product, hence, causality is respected. The found inversion formula applied to the traced Einstein equation has thus the form of a fixed point equation. The proof of local existence and uniqueness of the solution of the semiclassical Einstein equation is then obtained applying the Banach fixed point theorem.

SQUEEZED STATE REPRESENTATION OF QUANTUM FLUCTUATIONS AND SEMICLASSICAL THEORY

1998 ◽  
Vol 13 (03) ◽  
pp. 165-172 ◽  
Author(s):  
P. K. SURESH ◽  
V. C. KURIAKOSE
Keyword(s):  
Anisotropic Pressure ◽  
Energy Tensor ◽  
Semiclassical Theory ◽  
Stress Energy Tensor ◽  
Squeezed State ◽  
State Representation ◽  
Expectation Values ◽  
Squeezed Vacuum ◽  
Stress Energy ◽  
Vacuum States

A squeezed state representation is constructed for each mode of a quantized scalar field in a classical spatially homogeneous anisotropic background cosmology. The expectation values of stress–energy tensor are calculated in squeezed vacuum states. The results for the fluctuations in energy density and anisotropic pressure are also presented.

scholarly journals A PROPOSED SCALE-DEPENDENT COSMOLOGY FOR THE INHOMOGENEOUS UNIVERSE

1996 ◽  
Vol 05 (03) ◽  
pp. 293-312 ◽  
Author(s):  
C.W. KIM ◽  
J. SONG
Keyword(s):  
Hubble Parameter ◽  
Globular Clusters ◽  
Observational Cosmology ◽  
Energy Tensor ◽  
Stress Energy Tensor ◽  
Inhomogeneous Universe ◽  
Stress Energy ◽  
Walker Metric ◽  
Age Of The Universe ◽  
The Universe

We propose a scale-dependent cosmology with the stress-energy tensor of viscous fluid, in which the Robertson-Walker metric and the Einstein equation are generalized in such a way that Ω0, H0 and the age of the Universe all become scale-dependent. Its implications on the observational cosmology and possible modifications of the standard Friedmann cosmology are discussed. For example, since the age of the Universe in this model depends on the local values of Ω0 and the Hubble parameter, the age of the locally open Universe even with the high value of hubble parameter can be long enough to accommodate the measured ages of the oldest stars and globular clusters.

scholarly journals Stress-energy tensor correlators from the world-sheet

2021 ◽  
Vol 2021 (3) ◽  
Author(s):  
Hanno Bertle ◽  
Andrea Dei ◽  
Matthias R. Gaberdiel
Keyword(s):  
Vertex Operator ◽  
Energy Tensor ◽  
Stress Energy Tensor ◽  
World Sheet ◽  
Stress Energy ◽  
The World

Abstract The large N limit of symmetric orbifold theories was recently argued to have an AdS/CFT dual world-sheet description in terms of an sl(2, ℝ) WZW model. In previous work the world-sheet state corresponding to the symmetric orbifold stress-energy tensor was identified. We calculate certain 2- and 3-point functions of the corresponding vertex operator on the world-sheet, and demonstrate that these amplitudes reproduce exactly what one expects from the dual symmetric orbifold perspective.

ON THE ELECTROMAGNETIC PERTURBATIONS OF A MULTICONICAL SPACETIME

1996 ◽  
Vol 11 (27) ◽  
pp. 2171-2177
Author(s):  
A.N. ALIEV
Keyword(s):  
Cosmic Strings ◽  
Energy Tensor ◽  
Stress Energy Tensor ◽  
Stress Energy ◽  
Electromagnetic Perturbations

The electromagnetic perturbations propagating in the multiconical spacetime of N parallel cosmic strings are described. The expression for vacuum average of the stress-energy tensor is reduced to a form involving only zero-spin-weighted perturbation modes.

scholarly journals Kerr-Newman stress-tensor from minimal coupling

2020 ◽  
Vol 2020 (12) ◽  
Author(s):  
Ming-Zhi Chung ◽  
Yu-tin Huang ◽  
Jung-Wook Kim
Keyword(s):  
Form Factor ◽  
Stress Tensor ◽  
Energy Tensor ◽  
Stress Energy Tensor ◽  
Minimal Coupling ◽  
Massive Spin ◽  
Stress Energy ◽  
Newman Black Hole ◽  
Higher Spin ◽  
The One

Abstract In this paper, we demonstrate that at leading order in post Minkowskian (PM) expansion, the stress-energy tensor of Kerr-Newman black hole can be recovered to all orders in spin from three sets of minimal coupling: the electric and gravitational minimal coupling for higher-spin particles, and the “minimal coupling” for massive spin-2 decay. These couplings are uniquely defined from kinematic consideration alone. This is shown by extracting the classical piece of the one-loop stress-energy tensor form factor, which we provide a basis that is valid to all orders in spin. The 1 PM stress tensor, and the metric in the harmonic gauge, is then recovered from the classical spin limit of the form factor.

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