scholarly journals Born–Infeld-type modified gravity

2019 ◽  
Vol 16 (05) ◽  
pp. 1950070
Author(s):  
S. I. Kruglov
Keyword(s):  
Modified Gravity ◽  
Dimensionless Parameter ◽  
Cosmological Parameters ◽  
Minkowski Spacetime ◽  
Exponential Model ◽  
De Sitter Spacetime ◽  
De Sitter ◽  
Starobinsky Model ◽  
Sitter Spacetime ◽  
The Universe

We propose and investigate the modified Born–Infeld-type gravity model with the function [Formula: see text]. At different values of the dimensionless parameter [Formula: see text], the action is converted into some models including general relativity ([Formula: see text]), the Starobinsky model ([Formula: see text]), the exponential model of gravity ([Formula: see text]), and a model proposed in [S. I. Kruglov, Born–Infeld-like modified gravity, Int. J. Theor. Phys. 52 (2013) 2477–2484; S. I. Kruglov, Notes on Born–Infeld-like modified gravity, Astrophys. Space Sci. 361 (2016) 73] ([Formula: see text]). A bound on the parameters, [Formula: see text][Formula: see text]cm2, are due to local tests. The constant curvature solutions are obtained, and we found the potential, and the mass of the scalaron in the Einstein frame. The model describes the inflation of the universe. The de Sitter spacetime is unstable and a Minkowski spacetime is stable. We investigate the cosmological parameters and some critical points of autonomous equations.

scholarly journals LITTLE RIP COSMOLOGICAL MODELS WITH TIME-DEPENDENT EQUATION OF STATE

2012 ◽  
Vol 27 (36) ◽  
pp. 1250210 ◽  
Author(s):  
I. BREVIK ◽  
V. V. OBUKHOV ◽  
K. E. OSETRIN ◽  
A. V. TIMOSHKIN
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Cosmological Models ◽  
Time Dependent ◽  
De Sitter Spacetime ◽  
De Sitter ◽  
Energy Models ◽  
Sitter Spacetime ◽  
The Universe ◽  
Far Future

Specific dark energy models, leading to the Little Rip (LR) cosmology in the far future, are investigated. Conditions for the occurrence of LR in terms of the parameters present in the proposed equation of state for the dark energy cosmic fluid are studied. Estimates about the time needed before the occurrence of the small singularity in the standard LR model in which the universe approaches the de Sitter spacetime asymptotically, are given.

scholarly journals Production of scalar particles in electric field on de Sitter expanding universe

2014 ◽  
Vol 29 (27) ◽  
pp. 1450138 ◽  
Author(s):  
Mihaela-Andreea Băloi
Keyword(s):  
Electric Field ◽  
Particle Production ◽  
Perturbation Methods ◽  
Transition Amplitude ◽  
Scalar Particle ◽  
De Sitter Spacetime ◽  
De Sitter ◽  
Scalar Particles ◽  
Sitter Spacetime ◽  
The Universe

The scalar particle production from vacuum in the presence of an electric field, on the de Sitter spacetime is studied. We use perturbation methods to define the transition amplitude. We obtain that the momentum is not conserved in this process. The probability density of pair production is computed by squaring the transition amplitude. Our graphical representations show that, the probability of scalar particle production was important only in the early stages of the universe, when Hubble's constant was very large in comparison with the mass of the particle. Also, we propose here a criterion for particle–antiparticle separation.

scholarly journals Gravitational thermodynamics of causal diamonds in (A)dS

2019 ◽  
Vol 7 (6) ◽  
Author(s):  
Theodore Jacobson ◽  
Manus Visser
Keyword(s):  
Killing Vector ◽  
Minkowski Spacetime ◽  
Conformal Killing ◽  
De Sitter Spacetime ◽  
Conformal Killing Vector ◽  
De Sitter ◽  
Thermodynamic Relation ◽  
Killing Field ◽  
Sitter Spacetime ◽  
Gravitational Thermodynamics

The static patch of de Sitter spacetime and the Rindler wedge of Minkowski spacetime are causal diamonds admitting a true Killing field, and they behave as thermodynamic equilibrium states under gravitational perturbations. We explore the extension of this gravitational thermodynamics to all causal diamonds in maximally symmetric spacetimes. Although such diamonds generally admit only a conformal Killing vector, that seems in all respects to be sufficient. We establish a Smarr formula for such diamonds and a ``first law" for variations to nearby solutions. The latter relates the variations of the bounding area, spatial volume of the maximal slice, cosmological constant, and matter Hamiltonian. The total Hamiltonian is the generator of evolution along the conformal Killing vector that preserves the diamond. To interpret the first law as a thermodynamic relation, it appears necessary to attribute a negative temperature to the diamond, as has been previously suggested for the special case of the static patch of de Sitter spacetime. With quantum corrections included, for small diamonds we recover the ``entanglement equilibrium'' result that the generalized entropy is stationary at the maximally symmetric vacuum at fixed volume, and we reformulate this as the stationarity of free conformal energy with the volume not fixed.

scholarly journals Primordial Dark Energy from a Condensate of Spinors in a 5D Vacuum

2013 ◽  
Vol 2013 ◽  
pp. 1-7
Author(s):  
Pablo Alejandro Sánchez ◽  
Mauricio Bellini
Keyword(s):  
Dark Energy ◽  
Energy Density ◽  
Inflationary Universe ◽  
De Sitter Spacetime ◽  
De Sitter ◽  
Dark Energy Density ◽  
Sitter Spacetime ◽  
Interesting Candidate ◽  
Expansion Of The Universe ◽  
The Universe

We explore the possibility that the expansion of the universe can be driven by a condensate of spinors which are free of interactions in a 5D relativistic vacuum defined in an extended de Sitter spacetime which is Riemann flat. The extra coordinate is considered as noncompact. After making a static foliation on the extra coordinate, we obtain an effective 4D (inflationary) de Sitter expansion which describes an inflationary universe. We found that the condensate of spinors studied here could be an interesting candidate to explain the presence of dark energy in the early universe. The dark energy density which we are talking about is poured into smaller subhorizon scales with the evolution of the inflationary expansion.

scholarly journals Stringy Bubbles Solve de Sitter Troubles

Universe ◽  
2021 ◽  
Vol 7 (10) ◽  
pp. 363
Author(s):  
Per Berglund ◽  
Tristan Hübsch ◽  
Djordje Minic
Keyword(s):  
Bubble Nucleation ◽  
Recent Analysis ◽  
Mass Hierarchy ◽  
De Sitter Spacetime ◽  
De Sitter ◽  
Positive Cosmological Constant ◽  
Accelerating Expansion ◽  
Sitter Spacetime ◽  
Expansion Of The Universe ◽  
The Universe

Finding four-dimensional de Sitter spacetime solutions in string theory has been a vexing quest ever since the discovery of the accelerating expansion of the universe. Building on a recent analysis of bubble-nucleation in the decay of (false-vacuum) AdS backgrounds where the interfacing bubbles themselves exhibit a de Sitter geometry we show that this resonates strongly with a stringy cosmic brane construction that naturally provides for an exponential mass-hierarchy and the localization of both gravity and matter, in addition to an exponentially suppressed positive cosmological constant. Finally, we argue that these scenarios can be realized in terms of a generalization of a small resolution of a conifold singularity in the context of a (Lorentzian) Calabi–Yau 5-fold, where the isolated (Lorentzian) two complex dimensional Fano variety is a four-dimensional de Sitter spacetime.

scholarly journals DE SITTER TRANSITIVITY, CONFORMAL TRANSFORMATIONS AND CONSERVATION LAWS

2014 ◽  
Vol 23 (04) ◽  
pp. 1450035 ◽  
Author(s):  
J. G. PEREIRA ◽  
A. C. SAMPSON ◽  
L. L. SAVI
Keyword(s):  
Variational Principles ◽  
Matrix Representation ◽  
Minkowski Spacetime ◽  
The Other ◽  
Conformal Transformations ◽  
De Sitter Spacetime ◽  
De Sitter ◽  
Matrix Representations ◽  
Sitter Group ◽  
Sitter Spacetime

Minkowski spacetime is transitive under ordinary translations, a transformation that do not have matrix representations. The de Sitter spacetime, on the other hand, is transitive under a combination of translations and proper conformal transformations, which do have a matrix representation. Such matrix, however, is not by itself a de Sitter generator: it gives rise to a conformal re-scaling of the metric, a transformation not belonging to the de Sitter group, and in general not associated with diffeomorphisms in spacetime. When dealing with variational principles and Noether's theorem in de Sitter spacetime, it is necessary to regularize the transformations in order to eliminate the conformal re-scaling of the metric.

scholarly journals INFLATIONARY DARK ENERGY FROM A CONDENSATE OF SPINORS IN A 5D VACUUM

2013 ◽  
Vol 22 (12) ◽  
pp. 1342028 ◽  
Author(s):  
PABLO ALEJANDRO SÁNCHEZ ◽  
MAURICIO BELLINI
Keyword(s):  
Dark Energy ◽  
Early Universe ◽  
Inflationary Universe ◽  
De Sitter Spacetime ◽  
De Sitter ◽  
Physical Origin ◽  
Sitter Spacetime ◽  
Interesting Candidate ◽  
Expansion Of The Universe ◽  
The Universe

What is the physical origin of dark energy? Could this energy be originated by other fields than the inflaton? In this paper, we explore the possibility that the expansion of the universe can be driven by a condensate of spinors. These spinors are free of interactions on five-dimensional (5D) relativistic vacuum in an extended de Sitter spacetime. The extra coordinate is considered as noncompact. After making a static foliation on the extra coordinate, we obtain an effective four-dimensional (4D) (inflationary) de Sitter expansion which describes an inflationary universe. In view of our results, we conclude that the condensate of spinors here studied could be an interesting candidate to explain the presence of dark energy in the early universe.

scholarly journals MINKOWSKI BRANE IN ASYMPTOTIC dS5 SPACETIME WITHOUT FINE-TUNING

2004 ◽  
Vol 19 (19) ◽  
pp. 1447-1451 ◽  
Author(s):  
ZHE CHANG ◽  
SHAO-XIA CHEN ◽  
XIN-BING HUANG
Keyword(s):  
Cosmological Constant ◽  
Minkowski Spacetime ◽  
Fine Tuning ◽  
Dimensional Manifold ◽  
De Sitter Spacetime ◽  
De Sitter ◽  
Positive Cosmological Constant ◽  
Coordinate Axis ◽  
Sitter Spacetime

We discuss properties of a three-brane in an asymptotic five-dimensional de Sitter spacetime. It is found that a Minkowski solution can be obtained without fine-tuning. In the model, the tiny observed positive cosmological constant is interpreted as a curvature of five-dimensional manifold, but the Minkowski spacetime, where we live, is a natural three-brane perpendicular to the fifth coordinate axis.

scholarly journals Cosmological particle creation beyond de Sitter

2019 ◽  
Vol 28 (09) ◽  
pp. 1930015 ◽  
Author(s):  
Sujoy K. Modak
Keyword(s):  
Dark Energy ◽  
Particle Creation ◽  
Vacuum State ◽  
De Sitter Spacetime ◽  
De Sitter ◽  
Central Focus ◽  
Sitter Spacetime ◽  
Multi Stage ◽  
Classical Behavior ◽  
The Universe

Over the years, de Sitter spacetime has been a central focus in studies involving quantum fields, for its importance in the early and late expansion stages of the universe. While de Sitter spacetime closely mimics characteristics of the inflationary and dark energy dominated universe, it does not help to understand the radiation and matter dominated expansions. In this paper, we revisit some recent works involving the author which study gravitational particle creation beyond the de Sitter stage. Specifically, we present novel aspects of particle creation in the radiation dominated universe and then provide an analysis of time evolution of the primordial (Bunch–Davies) vacuum state, its particle excitation and quantum versus classical behavior of field modes in a multi-stage universe, comprising of (i) the inflationary de Sitter (ii) the radiation dominated and (iii) the late dark energy dominated stages.

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