NONMINIMAL COUPLING, QUARTIC POTENTIAL AND PERFECT FLUID COSMOLOGIES

1995 ◽  
Vol 04 (06) ◽  
pp. 767-779 ◽  
Author(s):  
S. CAPOZZIELLO ◽  
R. DE RITIS ◽  
C. RUBANO ◽  
P. SCUDELLARO
Keyword(s):  
Scalar Field ◽  
Equation Of State ◽  
Exact Solutions ◽  
Perfect Fluid ◽  
Einstein Gravity ◽  
Nonminimal Coupling ◽  
Stiff Matter ◽  
Quartic Potential ◽  
Fluid Matter

Perfect-fluid matter, satisfying the equation of state p=(γ−1)ρ, is considered in cosmologies where the geometry is nonminimally coupled with a scalar field ɸ and the potential of ɸ is λɸ4+Λ. Exact solutions are found when γ is a constant describing the ordinary forms of matter (γ=1, dust, γ=4/3, radiation, γ=2, stiff matter and γ=0, scalar field matter) and a discussion is done in order to recover Einstein gravity and the Newton constant observed today. The various solutions can be classified according to the different values of γ, λ and Λ.

EXACT SOLUTIONS IN BRANS-DICKE MATTER COSMOLOGIES

1996 ◽  
Vol 05 (01) ◽  
pp. 85-98 ◽  
Author(s):  
S. CAPOZZIELLO ◽  
R. DE RITIS ◽  
C. RUBANO ◽  
P. SCUDELLARO
Keyword(s):  
Exact Solutions ◽  
Perfect Fluid ◽  
State Equation ◽  
The State ◽  
Nonminimal Coupling ◽  
Ordinary Matter ◽  
Fluid Matter

We investigate Brans-Dicke cosmology with perfect-fluid matter and give a method for selecting exact solutions parametrized by the constant γ of the state equation p=(γ−1)ρ and the parameter ξ of the nonminimal coupling in which the Brans-Dicke theory can be recast. In this sense, we can classify the solutions having and not having inflationary behavior in the presence of ordinary matter.

scholarly journals STRING DILATON FLUID COSMOLOGY

1999 ◽  
Vol 08 (02) ◽  
pp. 213-227 ◽  
Author(s):  
S. CAPOZZIELLO ◽  
G. LAMBIASE ◽  
R. CAPALDO
Keyword(s):  
Exact Solutions ◽  
Perfect Fluid ◽  
Spatial Dimension ◽  
State Equation ◽  
Einstein Gravity ◽  
Asymptotic Freedom ◽  
Spatial Curvature ◽  
Effective Coupling ◽  
Fluid Matter ◽  
Dimension Number

We investigate (n+1)-dimensional string–dilaton cosmology with effective dilaton potential in presence of perfect-fluid matter. We get exact solutions parametrized by the constant γ of the state equation p=(γ-1)ρ, the spatial dimension number n, the bulk of matter, and the spatial curvature constant k. Several interesting cosmological behaviours are selected. Finally we discuss the recovering of ordinary Einstein gravity starting from string dominated regime and a sort of asymptotic freedom due to string effective coupling.

scholarly journals Isotropic exact solutions in $$F(R,Y,\phi )$$ gravity via Noether symmetries

2021 ◽  
Vol 81 (2) ◽  
Author(s):  
Saira Waheed ◽  
Iqra Nawazish ◽  
M. Zubair
Keyword(s):  
Scalar Field ◽  
Exact Solutions ◽  
Field Potential ◽  
Noether Symmetries ◽  
Dynamical Equations ◽  
Curvature Invariant ◽  
Gauge Symmetries ◽  
Cosmic Evolution ◽  
Fluid Matter ◽  
Alpha Beta

AbstractThe present article investigates the existence of Noether and Noether gauge symmetries of flat Friedman–Robertson–Walker universe model with perfect fluid matter ingredients in a generalized scalar field formulation namely $$f(R,Y,\phi )$$ f ( R , Y , ϕ ) gravity, where R is the Ricci scalar and Y denotes the curvature invariant term defined by $$Y=R_{\alpha \beta }R^{\alpha \beta }$$ Y = R α β R α β , while $$\phi $$ ϕ represents scalar field. For this purpose, we assume different general cases of generic $$f(R,Y,\phi )$$ f ( R , Y , ϕ ) function and explore its possible forms along with field potential $$V(\phi )$$ V ( ϕ ) by taking constant and variable coupling function of scalar field $$\omega (\phi )$$ ω ( ϕ ) . In each case, we find non-trivial symmetry generator and its related first integrals of motion (conserved quantities). It is seen that due to complexity of the resulting system of Lagrange dynamical equations, it is difficult to find exact cosmological solutions except for few simple cases. It is found that in each case, the existence of Noether symmetries leads to power law form of scalar field potential and different new types of generic function. For the acquired exact solutions, we discuss the cosmology generated by these solutions graphically and discuss their physical significance which favors the accelerated expanding eras of cosmic evolution.

A note on generalized Robertson–Walker space-times

2016 ◽  
Vol 13 (06) ◽  
pp. 1650079 ◽  
Author(s):  
Carlo Alberto Mantica ◽  
Young Jin Suh ◽  
Uday Chand De
Keyword(s):  
Vector Field ◽  
Scalar Field ◽  
Perfect Fluid ◽  
Curvature Tensor ◽  
Weyl Tensor ◽  
Space Time ◽  
Stiff Matter ◽  
Conformal Curvature ◽  
Conformal Curvature Tensor ◽  
Mass Less Scalar Field

A generalized Robertson–Walker (GRW) space-time is the generalization of the classical Robertson–Walker space-time. In the present paper, we show that a Ricci simple manifold with vanishing divergence of the conformal curvature tensor admits a proper concircular vector field and it is necessarily a GRW space-time. Further, we show that a stiff matter perfect fluid space-time or a mass-less scalar field with time-like gradient and with divergence-free Weyl tensor are GRW space-times.

scholarly journals LRS Bianchi I model with perfect fluid equation-of-state

2019 ◽  
Vol 28 (03) ◽  
pp. 1950056 ◽  
Author(s):  
Vijay Singh ◽  
Aroonkumar Beesham
Keyword(s):  
Equation Of State ◽  
General Solution ◽  
Perfect Fluid ◽  
Vacuum Energy ◽  
Energy Model ◽  
Field Equations ◽  
Systematic Treatment ◽  
Fluid Equation ◽  
Stiff Matter ◽  
Bianchi I

The general solution of the field equations in LRS Bianchi-I spacetime with perfect fluid equation-of-state (EoS) is presented. The models filled with dust, vacuum energy, Zel’dovich matter and disordered radiation are studied in detail. A unified and systematic treatment of the solutions is presented, and some new solutions are found. The dust, stiff matter and disordered radiation models describe only a decelerated universe, whereas the vacuum energy model exhibits a transition from a decelerated to an accelerated phase.

scholarly journals Inflation and linear expansion in the radiation dominated era in Jordan–Brans–Dicke cosmology

2019 ◽  
Vol 28 (04) ◽  
pp. 1950066
Author(s):  
Medine Ildes ◽  
Metin Arik ◽  
Mikhail B. Sheftel
Keyword(s):  
Scalar Field ◽  
Cosmological Model ◽  
Linear Expansion ◽  
Closed Universe ◽  
Expanding Universe ◽  
Scale Invariant ◽  
Stiff Matter ◽  
Quartic Potential ◽  
Model Based

We present several features of a cosmological model based on the Brans–Dicke–Jordan–Thirry action which is scale invariant with a quartic potential for the Jordan scalar field. We show that the radiation dominated era starts with a closed universe which expands exponentially and the late radiation dominated era expands linearly. We find that there may be a scale-invariant phase with stiff matter between these two radiation dominated eras. The introduction of matter in the linearly expanding universe may cause deceleration or acceleration.

Sign in / Sign up

Export Citation Format

Share Document