scholarly journals Particle creation in flat Friedmann–Robertson–Walker (FRW) universe in the framework of f(T) gravity

2013 ◽  
Vol 91 (2) ◽  
pp. 168-174 ◽  
Author(s):  
M.R. Setare ◽  
M.J.S. Houndjo
Keyword(s):  
Particle Production ◽  
Particle Creation ◽  
Massless Particle ◽  
Vacuum State ◽  
Scalar Fields ◽  
Teleparallel Gravity ◽  
Ricci Scalar ◽  
Frw Universe ◽  
Torsion Scalar ◽  
Friedmann Robertson Walker

We study particle production in a flat Friedmann–Robertson–Walker universe in the framework of f(T) gravity. An exact power-law solution is obtained by solving the Friedmann equations and assuming that matter is minimally coupled with gravitation. The torsion scalar, T, appears to plays the same role as the curvature (Ricci scalar) in general relativity (GR) and its modified theories, f(R). Particularly, in the phantom phase, we observe that the vacuum state corresponds to a vanishing torsion scalar and particle production becomes important as the torsion scalar diverges. This aspect not only provides the equivalence between teleparallel gravity and GR, but also between their respective modified versions, f(T) and f(R), in the view of massless particle production phenomenon when matter is minimally coupled with gravity. However, when the gravitational and scalar fields are not minimally coupled, it appears that this similarity between the teleparallel gravity and GR may break down, because the torsion scalar no longer has the same time-dependent expression as the Ricci scalar.

scholarly journals Disformal Transformations in Modified Teleparallel Gravity

Symmetry ◽  
2020 ◽  
Vol 12 (1) ◽  
pp. 152 ◽  
Author(s):  
Alexey Golovnev ◽  
María José Guzmán
Keyword(s):  
General Relativity ◽  
Torsion Tensor ◽  
Teleparallel Gravity ◽  
Ricci Scalar ◽  
Gravity Models ◽  
Boundary Term ◽  
Jordan Frame ◽  
Explicit Formulas ◽  
Torsion Scalar ◽  
Geometric Objects

In this work, we explore disformal transformations in the context of the teleparallel equivalent of general relativity and modified teleparallel gravity. We present explicit formulas in components for disformal transformations of the main geometric objects in these theories such as torsion tensor, torsion vector and contortion. Most importantly, we consider the boundary term which distinguishes the torsion scalar from the Ricci scalar. With that we show for f ( T ) gravity that disformal transformations from the Jordan frame representation are unable to straightforwardly remove local Lorentz breaking terms that characterize it. However, we have shown that disformal transformations have interesting properties, which can be useful for future applications in scalar-torsion gravity models, among others.

Low redshift universe and a varying ghost dark energy

2016 ◽  
Vol 31 (09) ◽  
pp. 1650055 ◽  
Author(s):  
M. Khurshudyan
Keyword(s):  
Dark Energy ◽  
Large Scale ◽  
Particle Production ◽  
Canonical Quantization ◽  
Particle Creation ◽  
Massless Particle ◽  
Suggested Model ◽  
Ghost Dark Energy ◽  
Large Scale Universe ◽  
Theoretical Results

Recently, a phenomenological modification of ghost dark energy has been suggested and appropriate models of low redshift universe have been constructed. In this paper, we will consider a model of low redshift universe in General Relativity containing another model of varying ghost dark energy. In this model, an effective fluid is a radiation-like fluid in an early universe and evolves to quintessence dark energy in large scale universe. Cosmographic analysis of new model is performed and appropriate constraints on the parameters of the model are obtained. We have a look at suggested model via statefinder hierarchy in addition to thermodynamical description of it. We also study massless particle creation possibility in a radiation dominated universe of our cosmological model. According to our theoretical results, massless particle production is possible. To study particle creation, a straight analogy between quantization in Minkowski background and canonical quantization of a scalar field in curved dynamical backgrounds is taken into account.

scholarly journals Reconstruction of the New Agegraphic Polytropic Gas Dark Energy Model in the Flat Friedmann Robertson Walker (FRW) Universe

2021 ◽  
Vol 13 (3) ◽  
pp. 779-784
Author(s):  
P. Das ◽  
K. P. Singh
Keyword(s):  
Dark Energy ◽  
Dark Energy Model ◽  
Scalar Fields ◽  
Energy Model ◽  
Accelerated Expansion ◽  
Frw Universe ◽  
Agegraphic Dark Energy ◽  
New Agegraphic Dark Energy ◽  
Polytropic Gas ◽  
Friedmann Robertson Walker

In this paper, we study the Polytropic Gas Dark Energy model and New Agegraphic Dark Energy model in the flat Friedmann Robertson Walker (FRW) Universe and establish a correspondence between them for the scalar fields. This correspondence allows reconstructing the potential of the Polytropic Gas scalar fields and dynamics of the scalar fields according to the evolutions of the New Agegraphic Dark Energy, which describes the accelerated expansion of the Universe.

OSCILLATORY PHASE OF NONCLASSICAL THERMAL INFLATON IN FRW UNIVERSE

2010 ◽  
Vol 19 (07) ◽  
pp. 1147-1195 ◽  
Author(s):  
K. K. VENKATARATNAM ◽  
P. K. SURESH
Keyword(s):  
Particle Production ◽  
Particle Creation ◽  
Squeezed States ◽  
Semiclassical Theory ◽  
Squeezed State ◽  
Nonclassical States ◽  
Frw Universe ◽  
Semiclassical Gravity ◽  
Oscillatory Phase ◽  
Classical Gravity

A minimally coupled nonclassical homogeneous scalar field is examined in the flat FRW universe in the semiclassical theory of gravity. Particle production in thermal coherent and squeezed states is studied for the flat FRW universe, in the oscillatory phase of the inflaton. Solutions for the semiclassical Friedmann equations are obtained in the thermal nonclassical states. Validity of the semiclassical theory is examined in the thermal coherent and squeezed states in the oscillatory phase of inflaton. Particle creation can be enhanced due to thermal and quantum effects. Quantum fluctuations of the inflaton in thermal coherent and squeezed state formalisms are also studied. Classical gravity differ from semiclassical gravity in the thermal coherent state only by an amplitude factor.

scholarly journals MASSIVE PARTICLE CREATION IN A STATIC (1 + 1)-DIMENSIONAL SPACE-TIME

1994 ◽  
Vol 09 (31) ◽  
pp. 2857-2869
Author(s):  
D. J. LAMB ◽  
A. Z. CAPRI ◽  
S. M. ROY
Keyword(s):  
Coordinate System ◽  
Particle Production ◽  
Dimensional Space ◽  
Massive Particle ◽  
Particle Creation ◽  
Vacuum State ◽  
Space Time ◽  
Physical Principle ◽  
Dimensional Space Time ◽  
Static Space

We show explicitly that there is particle creation in a static space-time. This is done by studying the field in a coordinate system based on a physical principle which has recently been proposed. There the field is quantized by decomposing it into positive and negative frequency modes on a particular space-like surface. This decomposition depends explicitly on the surface where the decomposition is performed, so that an observer who travels from one surface to another will observe particle production due to the different vacuum state.

Quantum fluctuations and particle production in the oscillatory phase of a thermal inflaton in a FRW universe

2019 ◽  
Vol 35 (06) ◽  
pp. 2050022 ◽  
Author(s):  
Renu Dhayal ◽  
Meghna Rathore ◽  
K. K. Venkataratnam
Keyword(s):  
Scalar Field ◽  
Einstein Equation ◽  
Particle Production ◽  
Particle Creation ◽  
Quantum Fluctuations ◽  
Oscillatory Behavior ◽  
Thermal Vacuum ◽  
Frw Universe ◽  
Oscillatory Phase ◽  
Thermal States

By the use of coherent and squeezed thermal states formalism, we analyzed the phenomena of particle creation when coherently oscillating a homogeneous scalar field (Inflaton) in semi-classical gravity. We also obtained an estimated solution for the semi-classical Einstein equation in non-classical thermal states formalism perturbatively, which is similar to the power-law expansion of classical Einstein equation. This solution, apart from a particular condition, shows oscillatory behavior in nature. We also analyzed a coherently oscillating homogeneous scalar field, in a thermal vacuum, coherent thermal, squeezed thermal vacuum and coherent squeezed thermal states, suffering from particle creation, and created particles are showing oscillatory behavior. Particle production can be raised due to thermal and quantum effects. We also studied quantum fluctuations of a homogeneous scalar field in the above-mentioned non-classical thermal states.

Extended scalar–tensor theory and thermodynamics in teleparallel framework

2016 ◽  
Vol 31 (33) ◽  
pp. 1650185 ◽  
Author(s):  
Mustafa Salti ◽  
Oktay Aydogdu ◽  
Irfan Acikgoz
Keyword(s):  
Lagrangian Density ◽  
Scalar Fields ◽  
Teleparallel Gravity ◽  
The Other ◽  
Field Energy ◽  
Field Equations ◽  
Energy Effect ◽  
Tensor Theory ◽  
Equilibrium Profiles ◽  
Friedmann Robertson Walker

We present here a new modified gravitation theory for the galactic dark energy effect by using a general Lagrangian density which is represented by an arbitrary function f(T, [Formula: see text], X) where T describes the torsion scalar in teleparallel gravity while X shows the kinetic scalar field energy. While the function is in general form, once reduced, the model can be transformed into some of the other well-known gravitation theories. After deriving the corresponding field equations and considering the flat Friedmann–Robertson–Walker type universe which is filled with ordinary cosmic matter, we discuss both the non-equilibrium and equilibrium profiles of galactic thermodynamics. We find that there exists an equilibrium picture of thermodynamics. Additionally, we also generalize ordinary f(T, [Formula: see text], X) model’s action to the case in which there exists an interaction between the chameleon and scalar fields.

GENERATING Λ FROM THE VACUUM

1999 ◽  
Vol 14 (33) ◽  
pp. 2269-2275 ◽  
Author(s):  
VARUN SAHNI
Keyword(s):  
Cosmological Constant ◽  
Vacuum Energy ◽  
Particle Production ◽  
Particle Creation ◽  
Scalar Fields ◽  
Momentum Tensor ◽  
Inflationary Universe ◽  
Static Universe ◽  
Effective Cosmological Constant ◽  
Close Relationship

The close relationship between the cosmological constant and the vacuum has been emphasized in the past by Zeldovich amongst others. We briefly discuss different approaches to the cosmological constant issue including the possibility that Λ could be generated by vacuum polarization in a static universe. Fresh possibilities occur in an expanding universe. An inflationary universe generically leads to particle creation from the vacuum, the nature and extent of particle production depending upon the mass of the field and its coupling to gravity. For ultra-light, non-minimally coupled scalar fields, particle production can be large and the resulting vacuum energy–momentum tensor will have the form of an effective cosmological constant. The inflationary scenario therefore, could give rise to a universe that is both flat andΛ-dominated, in agreement with observations.

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 A Quantum Kinetic Equation for Particle Production in the Schwinger Mechanism

1998 ◽  
Vol 07 (06) ◽  
pp. 709-722 ◽  
Author(s):  
S. Schmidt ◽  
D. Blaschke ◽  
G. Röpke ◽  
S. A. Smolyansky ◽  
A. V. Prozorkevich ◽  
...  
Keyword(s):  
Kinetic Equation ◽  
Particle Production ◽  
Source Term ◽  
Particle Creation ◽  
Pair Creation ◽  
Density Approximation ◽  
Quantum Kinetic Equation ◽  
Homogeneous Electric Field ◽  
Collisional Damping ◽  
Schwinger Mechanism

A quantum kinetic equation is derived for the description of pair production in a time-dependent homogeneous electric field E(t). As a source term, the Schwinger mechanism for particle creation is incorporated. Possible particle production due to collisions and collisional damping are neglected. The main result is a kinetic equation of non-Markovian character. In the low density approximation, the source term is reduced to the leading part of the well known Schwinger formula for the probability of pair creation. We discuss the momentum and time dependence of the derived source term and compare with other approaches.

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