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.

scholarly journals COSMOLOGY IN NONLINEAR BORN–INFELD SCALAR FIELD THEORY WITH NEGATIVE POTENTIALS

2007 ◽  
Vol 22 (12) ◽  
pp. 2173-2195 ◽  
Author(s):  
WEI FANG ◽  
H. Q. LU ◽  
Z. G. HUANG
Keyword(s):  
Field Theory ◽  
Scalar Field ◽  
Upper Bound ◽  
Expanding Universe ◽  
Scalar Field Theory ◽  
Stiff Matter ◽  
Ordinary Matter ◽  
Cosmological Solutions ◽  
Potential Parameters ◽  
Linear Scalar

The cosmological evolution in Nonlinear Born–Infeld (hereafter NLBI) scalar field theory with negative potentials was investigated. The cosmological solutions in some important evolutive epoches were obtained. The different evolutional behaviors between NLBI and linear (canonical) scalar field theory have been presented. A notable characteristic is that NLBI scalar field behaves as ordinary matter nearly the singularity while the linear scalar field behaves as "stiff" matter. We find that in order to accommodate current observational accelerating expanding universe the value of potential parameters |m| and |V0| must have an upper bound. We compare different cosmological evolutions for different potential parameters m, V0.

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.

Tachyon scalar field in a braneworld cosmology

2018 ◽  
Vol 33 (34) ◽  
pp. 1845017 ◽  
Author(s):  
Dragoljub D. Dimitrijevic ◽  
Neven Bilić ◽  
Goran S. Djordjevic ◽  
Milan Milosevic ◽  
Marko Stojanovic
Keyword(s):  
Scalar Field ◽  
Cosmological Model ◽  
Power Law ◽  
Inverse Power ◽  
Warp Factor ◽  
Braneworld Cosmology ◽  
Model Based ◽  
Inverse Power Law ◽  
Cosmological Context

We analyze a tachyon cosmological model based on the dynamics of a 3-brane in the bulk of the second Randall–Sundrum model. This model contains extended general warp functions, i.e. generalized bulk geometry. We study a power law warp factor in cosmological context. This type of warp factor generates an inverse power law tachyonic potential.

scholarly journals Scale Invariance, Horizons, and Inflation

2021 ◽  
Author(s):  
Andre Maeder ◽  
Vesselin G Gueorguiev
Keyword(s):  
Scalar Field ◽  
Scale Invariance ◽  
Maxwell Equations ◽  
High Redshift ◽  
Empty Space ◽  
Causal Connection ◽  
Cosmological Constant Problem ◽  
Scale Invariant ◽  
Starting Point ◽  
Final Answer

Abstract Maxwell equations and the equations of General Relativity are scale invariant in empty space. The presence of charge or currents in electromagnetism or the presence of matter in cosmology are preventing scale invariance. The question arises on how much matter within the horizon is necessary to kill scale invariance. The scale invariant field equation, first written by Dirac in 1973 and then revisited by Canuto et al. in 1977, provides the starting point to address this question. The resulting cosmological models show that, as soon as matter is present, the effects of scale invariance rapidly decline from ϱ = 0 to ϱc, and are forbidden for densities above ϱc. The absence of scale invariance in this case is consistent with considerations about causal connection. Below ϱc, scale invariance appears as an open possibility, which also depends on the occurrence of in the scale invariant context. In the present approach, we identify the scalar field of the empty space in the Scale Invariant Vacuum (SIV) context to the scalar field ϕ in the energy density $\varrho = \frac{1}{2} \dot{\varphi }^2 + V(\varphi )$ of the vacuum at inflation. This leads to some constraints on the potential. This identification also solves the so-called “cosmological constant problem”. In the framework of scale invariance, an inflation with a large number of e-foldings is also predicted. We conclude that scale invariance for models with densities below ϱc is an open possibility; the final answer may come from high redshift observations, where differences from the ΛCDM models appear.

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