scholarly journals Role of extended gravity theory in matter bounce dynamics

2022 ◽  
Author(s):  
A.S. Agrawal ◽  
S K Tripathy ◽  
Sarmistha Pal ◽  
B Mishra
Keyword(s):  
Big Bang ◽  
Gravity Theory ◽  
Geometrical Parameters ◽  
Extended Gravity ◽  
Dynamical Parameters ◽  
Frame Work ◽  
The Stability ◽  
The Big Bang ◽  
Bouncing Cosmologies

Abstract In this work, we have studied some bouncing cosmologies in the frame work of $f(R,T)$ gravity. The bouncing scenario has been formulated to avoid the big bang singularity. The physical and geometrical parameters are investigated. The effect of the extended gravity theory on the dynamical parameters of the model is investigated. It is found that, the $f(R,T)$ gravity parameter affects the cosmic dynamics substantially. We have also, tested the model through the calculation of the cosmographic coefficients and the $Om(z)$ parameter. A scalar field reconstruction of the bouncing scenario is also carried out. The stability of the model are tested under linear, homogeneous and isotropic perturbations.

scholarly journals On the stability of Einstein universe in f(R, T, Rμν Tμν) gravity

2018 ◽  
Vol 33 (36) ◽  
pp. 1850216 ◽  
Author(s):  
M. Sharif ◽  
Arfa Waseem
Keyword(s):  
State Parameter ◽  
Big Bang ◽  
Graphical Analysis ◽  
Momentum Tensor ◽  
Field Equations ◽  
Einstein Universe ◽  
Existence And Stability ◽  
The Stability ◽  
The Big Bang ◽  
Big Bang Singularity

This paper investigates the existence and stability of Einstein universe in the context of f(R, T, Q) gravity, where Q = R[Formula: see text] T[Formula: see text]. Considering linear homogeneous perturbations around scale factor and energy density, we formulate static as well as perturbed field equations. We parametrize the stability regions corresponding to conserved as well as non-conserved energy–momentum tensor using linear equation of state parameter for particular models of this gravity. The graphical analysis concludes that for a suitable choice of parameters, stable regions of the Einstein universe are obtained which indicates that the big bang singularity can be avoided successfully by the emergent mechanism in non-minimal matter-curvature coupled gravity.

scholarly journals Kantowski–Sachs Tsallis holographic dark energy model with sign-changeable interaction

2021 ◽  
Vol 81 (11) ◽  
Author(s):  
Y. Sobhanbabu ◽  
M. Vijaya Santhi
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Deceleration Parameter ◽  
Graphical Representation ◽  
Holographic Dark Energy ◽  
State Parameter ◽  
Field Equations ◽  
Dynamical Parameters ◽  
Frame Work ◽  
The Stability

AbstractIn this work devoted to the investigation of the Tsallis holographic dark energy (IR cut-off is Hubble radius) in homogeneous and anisotropic Kantowski–Sachs Universe within the frame-work of Saez–Ballester scalar tensor theory of gravitation. We have constructed non-interacting and interacting Tsallis holographic dark energy models by solving the field equations using the relationship between the metric potentials. This relation leads to a viable deceleration parameter model which exhibits a transition of the Universe from deceleration to acceleration. In interacting case, we focus on sign-changeable interaction between Tsallis holographic dark energy and dark matter. The dynamical parameters like equation of state parameter, energy densities of Tsallis holographic dark energy and dark matter, deceleration parameter, and statefinder parameters of the models are explained through graphical representation. And also, we discussed the stability analysis of the our models.

scholarly journals Cosmology at the top of the α′ tower

2021 ◽  
Vol 2021 (7) ◽  
Author(s):  
Jerome Quintin ◽  
Heliudson Bernardo ◽  
Guilherme Franzmann
Keyword(s):  
Energy Condition ◽  
Big Bang ◽  
Null Energy Condition ◽  
Einstein Frame ◽  
Accelerated Expansion ◽  
De Sitter ◽  
The Big Bang ◽  
Big Bang Singularity ◽  
Matter Sector

Abstract The cosmology of the fully α′-corrected duality-invariant action for the Neveu-Schwarz sector of string theory is revisited, with special emphasis on its coupling to matter sources. The role of the duality covariant pressure and dilatonic charge of the matter sector is explored in various contexts, from the low-curvature regime to non-perturbative solutions in α′. We comment on how an infinite tower of α′ corrections allows for fixed-dilaton de Sitter solutions, even in vacuum. We further investigate the necessary conditions for accelerated expansion in the Einstein frame, as well as for non-singular bounces that could resolve the big bang singularity. In particular, explicit examples are constructed, which show that the tower of α′ corrections may support an Einstein-frame non-singular cosmological bouncing background, even when the matter sector respects the null energy condition.

Origins of Gravitational Waves and Detectors

2020 ◽  
pp. 88-107
Author(s):  
John W. Moffat
Keyword(s):  
Black Holes ◽  
Neutron Stars ◽  
Gravitational Waves ◽  
Radio Telescope ◽  
Big Bang ◽  
Gravity Theory ◽  
Primordial Gravitational Waves ◽  
The Big Bang ◽  
The Waves

Civita criticized Einstein’s papers on gravitational waves: their energy momentum is frame dependent and therefore does not fit the covariance of Einstein’s gravity theory. Infeld and Rosen did not believe gravitational waves existed, and Einstein changed his mind on their existence repeatedly. Others did believe in them, such as Fock and Feynman. Weber constructed his “Weber bar” to detect gravitational waves, but when he claimed success, he was criticized. He then proposed using a Michelson-Morley type of interferometer with lasers to detect gravitational waves, as did Weiss. Merging black holes and neutron stars were proposed as detectable sources of gravitational waves. Taylor and Hulse, using the large Arecibo radio telescope, indirectly detected gravitational waves from inspiraling neutron stars. Primordial gravitational waves, still emanating from the Big Bang, were claimed to have been detected by BICEP2, but the waves were eventually shown to be a result of foreground dust.

scholarly journals Limitations of Observational Cosmology

1990 ◽  
Vol 123 ◽  
pp. 543-550
Author(s):  
Menas Kafatos
Keyword(s):  
Theoretical Models ◽  
Big Bang ◽  
Theoretical Physics ◽  
Observational Cosmology ◽  
Observable Universe ◽  
Fundamental Properties ◽  
Distant Galaxies ◽  
The Big Bang ◽  
The Universe

AbstractUnlike the usual situation with theoretical physics which is testable in the laboratory, in cosmological theories of the universe one faces the following problems: The observer is part of the system, the universe, and this system cannot be altered to test physical theory. Even though one can in principle consider any part of the observable universe as separate from the acts of observation, the very hypothesis of big bang implies that in the distant past, space-time regions containing current observers were part of the same system. One, therefore, faces a situation where the observer has to be considered as inherently a part of the entire system. The existence of horizons of knowledge in any cosmological view of the universe is then tantamount to inherent observational limits imposed by acts of observation and theory itself. For example, in the big bang cosmology the universe becomes opaque to radiation early on, and the images of extended distant galaxies merge for redshifts, z, of the order of a few. Moreover, in order to measure the distance of a remote galaxy to test any cosmological theory, one has to disperse its light to form a spectrum which would cause confusion with other background galaxies. Since the early universe should be described in quantum terms, it follows that the same problems regarding quantum reality and the role of the observer apply to the universe as a whole. One of the most fundamental properties of quantum theory, non-locality, may then apply equally well to the universe. Some of the problems facing big bang cosmology, like the horizon and flatness problems, may not then be preconditions on theoretical models but may instead be the manifestations of the quantum nature of the universe.

scholarly journals Anisotropic quantum cosmology with minimally coupled scalar field

2019 ◽  
Vol 34 (34) ◽  
pp. 1950283 ◽  
Author(s):  
Saumya Ghosh ◽  
Sunandan Gangopadhyay ◽  
Prasanta K. Panigrahi
Keyword(s):  
Scalar Field ◽  
Wave Packet ◽  
Quantum Cosmology ◽  
Hamiltonian Formalism ◽  
Big Bang ◽  
Type I ◽  
The Big Bang ◽  
The Universe ◽  
Big Bang Singularity

In this paper, we perform the Wheeler–DeWitt quantization for Bianchi type I anisotropic cosmological model in the presence of a scalar field minimally coupled to the Einstein–Hilbert gravity theory. We also consider the cosmological (perfect) fluid to construct the matter sector of the model whose dynamics plays the role of time. After obtaining the Wheeler–DeWitt equation from the Hamiltonian formalism, we then define the self-adjointness relations properly. Doing that, we proceed to get a solution for the Wheeler–DeWitt equation and construct a well-behaved wave function for the universe. The wave packet is next constructed from a superposition of the wave functions with different energy eigenvalues together with a suitable weight factor which renders the norm of the wave packet finite. It is then concluded that the Big-Bang singularity can be removed in the context of quantum cosmology.

scholarly journals Of Cosmic Background Anisotropies

1996 ◽  
Vol 168 ◽  
pp. 31-44
Author(s):  
G.F. Smoot
Keyword(s):  
Large Scale ◽  
Thermal Emission ◽  
Big Bang ◽  
Microwave Background ◽  
The Standard Model ◽  
The Big Bang ◽  
The Universe ◽  
Fundamental Physical ◽  
Large Scale Structure Formation

Observations of the Cosmic Microwave Background (CMB) Radiation have put the standard model of cosmology, the Big Bang, on firm footing and provide tests of various ideas of large scale structure formation. CMB observations now let us test the role of gravity and General Relativity in cosmology including the geometry, topology, and dynamics of the Universe. Foreground galactic emissions, dust thermal emission and emission from energetic electrons, provide a serious limit to observations. Nevertheless, observations may determine if the evolution of the Universe can be understood from fundamental physical principles.

De Sitter and bounce solutions from anisotropy in extended gravity cosmology

2019 ◽  
Vol 34 (39) ◽  
pp. 1950321 ◽  
Author(s):  
B. Mishra ◽  
G. Ribeiro ◽  
P. H. R. S. Moraes
Keyword(s):  
Big Bang ◽  
Late Time ◽  
Type I ◽  
De Sitter ◽  
Field Equations ◽  
Extended Gravity ◽  
Numerical Fitting ◽  
De Sitter Universe ◽  
The Big Bang ◽  
The Universe

We investigate the consequences of incepting the Bianchi type I metric in the [Formula: see text] gravity theory field equations. We particularly derive solutions for a matter-dominated universe. From such a scenario, it is possible to predict a late-time de Sitter universe. Moreover, depending on the numerical fitting function for the scale factor, the universe is predicted to bounce and evade the Big Bang singularity.

Can Quantum Measurements Control Temperature?

2020 ◽  
pp. 189-202
Author(s):  
Gershon Kurizki ◽  
Goren Gordon
Keyword(s):  
Quantum Effects ◽  
Big Bang ◽  
Quantum Measurements ◽  
Environment Interaction ◽  
Hot Environment ◽  
Time Flow ◽  
Time Arrow ◽  
The Big Bang ◽  
Measurement Rate

Henry is trapped in a burning building because of Eve’s mischief. Henry’s entanglement with the hot environment is ominous: his states receive excessive energy from the environment, threatening his physiology. Can quantum effects rescue Henry from the fire? Unexpectedly, Eve comes to his rescue. She frequently measures his energy in a “quantum non-demolition” (QND) fashion which is expected to keep his state intact. Surprisingly, Henry grows hotter or colder depending on Eve’s measurement rate! These quantum effects seem to violate the laws of thermodynamics. Engraved in stone as these laws and the ensuing time directionality (time arrow) may be, they fail if the system is examined too frequently, whence time arrow loses its meaning. One may speculate over the role of such anomalies in the Big Bang. These anomalies support Parmenides’ view that time flow is determined by the observer’s choices. The appendix to this chapter elaborates on the dynamics induced by system–environment interaction changes.

Sign in / Sign up

Export Citation Format

Share Document