scholarly journals Energy Conditions of Built-In Inflation Models inf(T)Gravitational Theories

2015 ◽  
Vol 2015 ◽  
pp. 1-10
Author(s):  
Gamal G. L. Nashed
Keyword(s):  
Flat Space ◽  
Space Time ◽  
Energy Conditions ◽  
Frw Universe ◽  
Open Universe ◽  
Gravitational Theories ◽  
Friedmann Robertson Walker

We examine the validity of energy conditions of built-in inflation models inf(T)gravitational theories. For this purpose, we formulate the inequalities of energy conditions by assuming the flat and nonflat Friedmann-Robertson-Walker (FRW) universe. We find the feasible constraints on the constants of integration and evaluate their possible ranges graphically for the consistency of these energy conditions for flat, closed, and open universes. We constrain the constants of integration for flat space-time from the inflation epoch while the closed and open universe constants are constrained from late universe.

Tensorial rank of gravitational theories in flat space-time

1983 ◽  
Vol 75 (1) ◽  
pp. 50-56 ◽  
Author(s):  
G. Cavalleri ◽  
G. Spinelli
Keyword(s):  
Flat Space ◽  
Space Time ◽  
Gravitational Theories

C-field cosmology for barotropic fluid distribution with variable bulk viscosity and vacuum energy (Λ) in Friedmann–Robertson–Walker (FRW) space–time

2015 ◽  
Vol 93 (1) ◽  
pp. 14-17
Author(s):  
Raj Bali ◽  
Seema Saraf
Keyword(s):  
Bulk Viscosity ◽  
Vacuum Energy ◽  
Big Bang ◽  
Negative Energy ◽  
Space Time ◽  
Energy Conditions ◽  
Fluid Distribution ◽  
Massless Scalar ◽  
Barotropic Fluid ◽  
Friedmann Robertson Walker

A cosmological model that admits barotropic fluid distribution and a negative energy massless scalar creation field as a source in the presence of bulk viscosity and vacuum energy (Λ) in Friedmann–Robertson–Walker space–time is investigated. It has been shown that the model satisfies observational tests and is thus an alternative to the standard Big Bang model. The model is free from real singularity and particle horizon. The creation field increases with time, which matches Hoyle and Narlikar (Proc. Roy. Soc. A, 282, 178 (1964). doi:10.1098/rspa.1964.0225 ). To get the deterministic results, we have assumed that the coefficient of bulk viscosity, ζαρ1/2, where ρ is the matter density, ρ = 3H2, Λ ∼ H2, where H is the Hubble parameter. The model satisfies the energy conditions (weak, dominant, and strong). The deceleration parameter, q < 0, shows that the model represents an accelerating phase of the universe.

Dark energy model in higher-dimensional FRW universe with respect to generalized entropy of Sharma and Mittal of flat FRW space–time

2019 ◽  
Vol 97 (11) ◽  
pp. 1185-1186 ◽  
Author(s):  
E.C. Gunay Demirel
Keyword(s):  
Dark Energy ◽  
Dark Energy Model ◽  
State Parameter ◽  
Space Time ◽  
Observational Evidence ◽  
The State ◽  
Frw Universe ◽  
Generalized Entropy ◽  
Higher Dimensional ◽  
Friedmann Robertson Walker

In this study, we report the state parameter of dark energy in higher dimensional Friedmann–Robertson–Walker (FRW) space–time according to generalized entropy of Sharma and Mittal. In this case we analyze the state parameter of dark energy according to today’s observational evidence.

scholarly journals HAWKING-LIKE RADIATION AS TUNNELING FROM THE APPARENT HORIZON IN AN FRW UNIVERSE

2010 ◽  
Vol 19 (02) ◽  
pp. 159-169 ◽  
Author(s):  
TAO ZHU ◽  
JI-RONG REN ◽  
DOUGLAS SINGLETON
Keyword(s):  
Black Hole Physics ◽  
Apparent Horizon ◽  
Space Time ◽  
Frw Universe ◽  
Standard Result ◽  
Exterior Region ◽  
Tunneling Method ◽  
Usual Quantum ◽  
The Relationship ◽  
Friedmann Robertson Walker

We study Hawking-like radiation in a Friedmann–Robertson–Walker (FRW) universe using the quasi-classical WKB/tunneling method, which pictures this process as a "tunneling" of particles from behind the apparent horizon. The correct temperature of the Hawking-like radiation from the FRW space–time is obtained using a canonical invariant tunneling amplitude. In contrast to the usual quantum-mechanical WKB/tunneling problem, where the tunneling amplitude has only a spatial contribution, we find that the tunneling amplitude for FRW space–time (i.e. the imaginary part of the action) has both spatial and temporal contributions. In addition we study backreaction and energy conservation of the radiated particles and find that the tunneling probability and the change in entropy, [Formula: see text], are related by the relationship [Formula: see text], which differs from the standard result, [Formula: see text]. By regarding the whole FRW universe as an isolated adiabatic system, the change in the total entropy is zero. Then, splitting the entropy between the interior and exterior parts of the horizon [Formula: see text], we can explain the origin of the minus sign difference with the usual result: our [Formula: see text] is for the interior region, while the standard result from black hole physics is for the exterior region.

scholarly journals Two theorems on flat space-time gravitational theories

1980 ◽  
Vol 12 (10) ◽  
pp. 825-835
Author(s):  
Mario Castagnino ◽  
Luis Chimento
Keyword(s):  
Flat Space ◽  
Space Time ◽  
Gravitational Theories

scholarly journals Almost-Pseudo-Ricci Symmetric FRW Universe with a Dynamic Cosmological Term and Equation of State

Universe ◽  
2021 ◽  
Vol 7 (7) ◽  
pp. 205
Author(s):  
Sanjay Mandal ◽  
Avik De ◽  
Tee-How Loo ◽  
Pradyumn Kumar Sahoo
Keyword(s):  
Equation Of State ◽  
Cosmological Parameters ◽  
Cosmological Term ◽  
Ricci Scalar ◽  
Energy Conditions ◽  
Late Time ◽  
Frw Universe ◽  
Accelerating Expansion ◽  
Expansion Of The Universe ◽  
The Universe

The objective of the present paper is to investigate an almost-pseudo-Ricci symmetric FRW spacetime with a constant Ricci scalar in a dynamic cosmological term Λ(t) and equation of state (EoS) ω(t) scenario. Several cosmological parameters are calculated in this setting and thoroughly studied, which shows that the model satisfies the late-time accelerating expansion of the universe. We also examine all of the energy conditions to check our model’s self-stability.

scholarly journals Flat Space-Time and Gravitation

1944 ◽  
Vol 30 (10) ◽  
pp. 324-334 ◽  
Author(s):  
G. D. Birkhoff
Keyword(s):  
Flat Space ◽  
Space Time
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