Formation Of Emergent Universe in Brane Scenario as a Consequence of Particle Creation (original) (raw)
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Emergent universe in the braneworld scenario
The European Physical Journal C, 2016
According to Padmanabhan's proposal, the difference between the surface degrees of freedom and the bulk degrees of freedom in a region of space may result in the acceleration of Universe expansion through the relation V / t = N sur − N bulk where N bulk and N sur are referred to the degrees of freedom related to the matter and energy content inside the bulk and surface area, respectively (Padmanabhan, arXiv:1206.4916v1, 2012). In this paper, we study the dynamical effect of the extrinsic geometrical embedding of an arbitrary four-dimensional brane in a higher-dimensional bulk space and investigate the corresponding degrees of freedom. Considering the modification of the Friedmann equations arising from a general braneworld scenario, we obtain a correction term in Padmanabhan's relation, denoting the number of degrees of freedom related to the extrinsic geometry of the brane embedded in higher-dimensional spacetime as V / t = N sur − N bulk − N extr where N extr is for the degree of freedom related to the extrinsic geometry of the brane, while N sur and N bulk are defined as before. Finally, we study the validity of the first and second laws of thermodynamics for this general braneworld scenario in the state of thermal equilibrium and in the presence of confined matter fields to the brane with the induced geometric matter fields.
Thermodynamics of gravitationally induced particle creation scenario in DGP braneworld
In this paper, we discuss the thermodynamical analysis for gravitationally induced particle creation scenario in the framework of DGP braneworld model. For this purpose, we consider apparent horizon as the boundary of the universe. We take three types of entropy such as Bakenstein entropy, logarithmic corrected entropy and power law corrected entropy with ordinary creation rate Γ. We analyze the first law and generalized second law of thermodynamics analytically for these entropies which hold under some constraints. The behavior of total entropy in each case is also discussed which implies the validity of generalized second law of thermodynamics. Also, we check the thermodynamical equilibrium condition for two phases of creation rate, that is constant and variable Γ and found its validity in all cases of entropy.
The present study, on the expansion of universe, is based on an assumption regarding the possibility of inter-conversion between matter and dark energy, through some interaction of matter with the scalar field in the framework of Brans-Dicke theory. The field equations for a spatially flat space-time have been solved using an empirical dependence of scalar field parameter upon the scale factor. To represent the behaviour regarding the non-conservation of matter, a function, expressed in terms of the Hubble parameter, has been empirically incorporated into the field equations. Their solution shows that, this function, whose value is proportional to the matter content of the universe, decreases monotonically with time. This matter-field interaction generates late time acceleration, causing the deceleration parameter to change its sign from positive to negative. Time dependence of the proportion of dark energy component of the universe has been determined and shown graphically. Time variation of gravitational constant and the Brans-Dicke dimensionless parameter has been analyzed in the present study. The rate of generation of dark energy from matter has been found to affect the time variations of deceleration parameter and gravitational constant.
The present study, on the expansion of universe, is based on an assumption regarding the possibility of inter-conversion between matter and dark energy, through some interaction of matter with the scalar field in the framework of Brans-Dicke theory. The field equations for a spatially flat space-time have been solved using an empirical dependence of scalar field parameter upon the scale factor. To represent the behaviour regarding the non-conservation of matter, a function, expressed in terms of the Hubble parameter, has been empirically incorporated into the field equations. Their solution shows that, this function, whose value is proportional to the matter content of the universe, decreases monotonically with time. This matter-field interaction generates late time acceleration, causing the deceleration parameter to change its sign from positive to negative. Time dependence of the proportion of dark energy component of the universe has been determined and shown graphically. Time variation of gravitational constant and the Brans-Dicke dimensionless parameter has been analyzed in the present study. The rate of generation of dark energy from matter has been found to affect the time variations of deceleration parameter and gravitational constant.
Stable emergent Universe - a creation without Big-Bang
Astronomische Nachrichten, 2015
Riemannian volume forms, global Weyl-scale symmetry spontaneous breakdown, flat regions of scalar potential, non-singular origin of the universe Based on an earlier introduced new class of generalized gravity-matter models defined in terms of two independent non-Riemannian volume forms (alternative generally covariant integration measure densities) on the space-time manifold, we derive an effective "Einstein-frame" theory featuring the following remarkable properties: (i) We obtain effective potential for the cosmological scalar field possessing two infinitely large flat regions which allows for a unified description of both early universe inflation as well as of present dark energy epoch; (ii) For a specific parameter range the model possesses a non-singular stable "emergent universe" solution which describes an initial phase of evolution that precedes the inflationary phase.
FRW in Cosmological Self-creation Theory
International Journal of Theoretical Physics, 2013
We use the Brans-Dicke theory from the framework of General Relativity (Einstein frame), but now the total energy momentum tensor fulfills the following condition 1 φ T µνM + T µν (φ) ;ν = 0. We take as a first model the flat FRW metric and with the law of variation for Hubble's parameter proposal by Berman [1], we find solutions to the Einstein field equations by the cases: inflation (γ = −1), radiation (γ = 1 3), stiff matter (γ = 1). For the Inflation case the scalar field grows fast and depends strongly of the constant Mγ=−1 that appears in the solution, for the Radiation case, the scalar stop its expansion and then decrease perhaps due to the presence of the first particles. In the Stiff Matter case, the scalar field is decreasing so for a large time, φ → 0. In the same line of classical solutions, we find an exact solution to the Einstein field equations for the stiff matter (γ = 1) and flat universe, using the Hamilton-Jacobi scheme.
Thermodynamics of cosmological matter creation
Proceedings of the National Academy of Sciences, 1988
A type of cosmological history that includes large-scale entropy production is proposed. These cosmologies are based on reinterpretation of the matter-energy stress tensor in Einstein's equations. This modifies the usual adiabatic energy conservation laws, thereby including irreversible matter creation. This creation corresponds to an irreversible energy flow from the gravitational field to the created matter constituents. This point of view results from consideration of the thermodynamics of open systems in the framework of cosmology. It is shown that the second law of thermodynamics requires that space-time transforms into matter, while the inverse transformation is forbidden. It appears that the usual initial singularity associated with the big bang is structurally unstable with respect to irreversible matter creation. The corresponding cosmological history therefore starts from an instability of the vacuum rather than from a singularity. This is exemplified in the framework of a simple phenomenological model that leads to a three-stage cosmology: the first drives the cosmological system from the initial instability to a de Sitter regime, and the last connects with the usual matter-radiation Robertson-Walker universe. Matter as well as entropy creation occurs during the first two stages, while the third involves the traditional cosmological evolution. A remarkable fact is that the de Sitter stage appears to be an attractor independent of the initial fluctuation. This is also the case for all the physical predictions involving the present Robertson-Walker universe. Most results obtained previously, in the framework of quantum field theory, can now be obtained on a macroscopic basis. It is shown that this description leads quite naturally to the introduction of primeval black holes as the intermediate stage between the Minkowski vacuum and the present matter-radiation universe. The instability at the origin of the universe is the result of fluctuations of the vacuum in which black holes act as membranes that stabilize these fluctuations. In short, black holes will be produced by an "inverse" Hawking radiation process and, once formed, will decompose into "real" matter through the usual Hawking radiation. In this way, the irreversible transformation of space-time into matter can be described as a phase separation between matter and gravitation in which black holes play the role of "critical nuclei."
Journal of Cosmology and Astroparticle Physics, 2014
We explore the possibility of emergent cosmology using the effective potential formalism. We discover new models of emergent cosmology which satisfy the constraints posed by the cosmic microwave background (CMB). We demonstrate that, within the framework of modified gravity, the emergent scenario can arise in a universe which is spatially open/closed. By contrast, in general relativity (GR) emergent cosmology arises from a spatially closed pasteternal Einstein Static Universe (ESU). In GR the ESU is unstable, which creates fine tuning problems for emergent cosmology. However, modified gravity models including Braneworld models, Loop Quantum Cosmology (LQC) and Asymptotically Free Gravity result in a stable ESU. Consequently, in these models emergent cosmology arises from a larger class of initial conditions including those in which the universe eternally oscillates about the ESU fixed point. We demonstrate that such an oscillating universe is necessarily accompanied by graviton production. For a large region in parameter space graviton production is enhanced through a parametric resonance, casting serious doubts as to whether this emergent scenario can be past-eternal.
A New Cosmological Model: Origin and Maintenance of the Universe
HAL (Le Centre pour la Communication Scientifique Directe), 2023
We wish to suggest an alternative physical origin and organisation of the universe contrasting with the Standard Model of Cosmology [ ]. The masses of Standard Model (SM) particles [ ] are 1 2 generated by interactions between a quantum field, and thermal and particle diffusion waves-the Thermon-PDW mechanism-a process which is observationally confirmed [ ]. An exact 3 "ensemble" of quantum fields responding to harmonic solutions of interacting thermal and particle diffusion waves [ , ] solves the problem of particle mass. However, this generates its own 4 5 complication: an obligatory requirement for a thermal source perfusing continuously throughout the universe. This constraint (and others) is accommodated by several properties of the principal hypothesis. Furthermore, if this interpretation is validated, it eliminates many difficulties due to the orthodox cosmological model, such as reverse engineering fundamental laws of physics, the initial singularity, initial high temperatures and densities and inflation; generally SMC as a whole should be discarded [1] together with other model possibilities, including string theory solutions, multiverse, quantum loop theories and physics beyond the Standard Model of Particles [ , ]. The 6 7
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The presence of a 4-form field in a fixed background spacetime can give rise to the creation of brane universes, that mimic the Swinger pair production. By means of a canonical quantum approach, we study the birth of a brane universe involving its intrinsic curvature. The nucleation probability for the brane is calculated taking into account both an instanton method and a WKB approximation. We discuss some cosmological implications resulting from the model.