scholarly journals Chameleon stars supported by a cosmological scalar field

2012 ◽  
Vol 86 (6) ◽  
Author(s):  
Vladimir Folomeev
Keyword(s):  
Scalar Field ◽  
Cosmological Scalar

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 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 PHANTOM UNIVERSE FROM CPT SYMMETRIC QFT

2006 ◽  
Vol 15 (08) ◽  
pp. 1299-1310 ◽  
Author(s):  
ALEXANDER A. ANDRIANOV ◽  
FRANCESCO CANNATA ◽  
ALEXANDER Y. KAMENSHCHIK
Keyword(s):  
Field Theory ◽  
Dark Energy ◽  
Scalar Field ◽  
Complex Potential ◽  
Vacuum Energy ◽  
Scalar Fields ◽  
Smooth Transition ◽  
Cpt Symmetry ◽  
Energy Equivalence ◽  
Cosmological Scalar

We develop a generalization of semiclassical field theory for the case of non-Hermitian Hamiltonians with CPT symmetry and construct a classical cosmological, scalar-field based model describing a smooth transition from ordinary dark energy to the phantom one. Our model arises from a Lagrangian with a complex potential leading to a non-trivial vacuum with real vacuum energy. Equivalence with models involving two scalar fields one of which is phantom-like is discussed.

scholarly journals Jacobi Stability Analysis of Scalar Field Models with Minimal Coupling to Gravity in a Cosmological Background

2016 ◽  
Vol 2016 ◽  
pp. 1-26 ◽  
Author(s):  
Bogdan Dănilă ◽  
Tiberiu Harko ◽  
Man Kwong Mak ◽  
Praiboon Pantaragphong ◽  
Sorin V. Sabau
Keyword(s):  
Stability Analysis ◽  
Scalar Field ◽  
Scalar Fields ◽  
Cosmological Evolution ◽  
Order System ◽  
Unstable State ◽  
Scalar Field Models ◽  
Klein Gordon ◽  
Cosmological Scalar ◽  
The Stability

We study the stability of the cosmological scalar field models by using the Jacobi stability analysis, or the Kosambi-Cartan-Chern (KCC) theory. In this approach, we describe the time evolution of the scalar field cosmologies in geometric terms, by performing a “second geometrization” and considering them as paths of a semispray. By introducing a nonlinear connection and a Berwald-type connection associated with the Friedmann and Klein-Gordon equations, five geometrical invariants can be constructed, with the second invariant giving the Jacobi stability of the cosmological model. We obtain all the relevant geometric quantities, and we formulate the condition for Jacobi stability in scalar field cosmologies. We consider the Jacobi stability properties of the scalar fields with exponential and Higgs type potential. The Universe dominated by a scalar field exponential potential is in Jacobi unstable state, while the cosmological evolution in the presence of Higgs fields has alternating stable and unstable phases. We also investigate the stability of the phantom quintessence and tachyonic scalar field models, by lifting the first-order system to the tangent bundle. It turns out that in the presence of a power law potential both of these models are Jacobi unstable during the entire cosmological evolution.

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