scholarly journals On the spatially homogeneous and isotropic Einstein-Vlasov-Fokker-Planck system with cosmological scalar field

2018 ◽  
Vol 11 (5) ◽  
pp. 1063-1083
Author(s):  
Simone Calogero ◽  
◽  
Stephen Pankavich ◽  
Keyword(s):  
Scalar Field ◽  
Spatially Homogeneous ◽  
Cosmological Scalar ◽  
Fokker Planck

Geometric phase of cosmological scalar and tensor perturbations in f(R) gravity

2018 ◽  
Vol 33 (14) ◽  
pp. 1850077
Author(s):  
Hamideh Balajany ◽  
Mohammad Mehrafarin
Keyword(s):  
Scalar Field ◽  
Harmonic Oscillator ◽  
Geometric Phase ◽  
Berry Phase ◽  
Time Dependent ◽  
Einstein Theory ◽  
Tensor Perturbations ◽  
Cosmological Scalar ◽  
Conformal Equivalence

By using the conformal equivalence of f(R) gravity in vacuum and the usual Einstein theory with scalar-field matter, we derive the Hamiltonian of the linear cosmological scalar and tensor perturbations in f(R) gravity in the form of time-dependent harmonic oscillator Hamiltonians. We find the invariant operators of the resulting Hamiltonians and use their eigenstates to calculate the adiabatic Berry phase for sub-horizon modes as a Lewis–Riesenfeld phase.

scholarly journals Wave-like spatially homogeneous models of Stäckel spacetimes (2.1) type in the scalar-tensor theory of gravity

2020 ◽  
Vol 35 (33) ◽  
pp. 2050275
Author(s):  
Konstantin Osetrin ◽  
Altair Filippov ◽  
Evgeny Osetrin
Keyword(s):  
Scalar Field ◽  
Explicit Form ◽  
Scalar Tensor Theory ◽  
Tensor Theory ◽  
Test Particles ◽  
Homogeneous Wave ◽  
General Scalar ◽  
Spatially Homogeneous ◽  
Theory Of Gravity ◽  
The Universe

Six exact solutions are obtained in the general scalar-tensor theory of gravity related to spatially homogeneous wave-like models of the Universe. Wave-like spacetime models allow the existence of privileged coordinate systems where the eikonal equation and the Hamilton–Jacobi equation of test particles can be integrated by the method of complete separation of variables with the separation of isotropic (wave) variables on which the space metric depends (non-ignored variables). An explicit form of the scalar field and two functions of the scalar field that are part of the general scalar-tensor theory of gravity are found. The explicit form of the eikonal function and the action function for test particles in the considered models is given. The obtained solutions are of type III according to the Bianchi classification and type N according to the Petrov classification. Wave-like spatially homogeneous spacetime models can describe primordial gravitational waves of the Universe.

scholarly journals DYNAMICS OF A GENERALIZED COSMOLOGICAL SCALAR–TENSOR THEORY

2002 ◽  
Vol 11 (05) ◽  
pp. 669-684 ◽  
Author(s):  
TAKAO FUKUI ◽  
JAMES M. OVERDUIN
Keyword(s):  
Scalar Field ◽  
Dimensional Space ◽  
Time Derivative ◽  
Analytic Solutions ◽  
Cosmological Term ◽  
Order Unity ◽  
Tensor Theory ◽  
Dimensional Space Time ◽  
Free Parameters ◽  
Cosmological Scalar

A generalized scalar–tensor (GST) theory is investigated whose cosmological (or quintessence) term depends on both a scalar field and its time derivative. A correspondence with solutions of five-dimensional Space–Time–Matter (STM) theory is noted. Analytic solutions are found for the scale factor, scalar field and cosmological term. Models with free parameters of order unity are consistent with recent observational data and could be relevant to both the dark matter and cosmological "constant" problems.

scholarly journals Spatially homogeneous solutions of the Vlasov–Nordström–Fokker–Planck system

2014 ◽  
Vol 257 (10) ◽  
pp. 3700-3729 ◽  
Author(s):  
José Antonio Alcántara Felix ◽  
Simone Calogero ◽  
Stephen Pankavich
Keyword(s):  
Homogeneous Solutions ◽  
Spatially Homogeneous ◽  
Fokker Planck

THERMAL SQUEEZING AND DENSITY FLUCTUATIONS IN SEMICLASSICAL THEORY OF GRAVITY

2001 ◽  
Vol 16 (11) ◽  
pp. 707-717 ◽  
Author(s):  
P. K. SURESH
Keyword(s):  
Scalar Field ◽  
Coherent State ◽  
Density Fluctuation ◽  
Density Fluctuations ◽  
Semiclassical Theory ◽  
Squeezed State ◽  
State Representation ◽  
Walker Metric ◽  
Spatially Homogeneous ◽  
Theory Of Gravity

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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