scholarly journals dS/CFT at uniform energy density and a de Sitter “bluewall”

2014 ◽  
Vol 2014 (4) ◽  
Author(s):  
Diptarka Das ◽  
Sumit R. Das ◽  
K. Narayan
2015 ◽  
Vol 30 (21) ◽  
pp. 1550105
Author(s):  
Zhonghua Li ◽  
Limei Zhang

It is known that for self-gravitating radiation stars in anti-de Sitter (AdS) spacetime, there is a critical dimension, larger than it, the stars always maintain stability with any central energy density [Formula: see text]; smaller than it, there is a maximal mass for the [Formula: see text] and when the [Formula: see text] continues to increase, the total mass of stars becomes a function of the [Formula: see text], and the function appears as an oscillation behavior and therefore the stars become unstable. In this paper we extend this study to the nonlinear case, in this case the equation of state is [Formula: see text], in AdS spacetime, where a and b are two constant parameters. For the nonlinear case,the equations of gravitational field are more complicated, so the relation of total mass to the central energy density is numerically investigated. In particular, the effect of the two parameters a and b and the relation between spacetime dimension d, mass and [Formula: see text] are analyzed. We find that the critical dimension changes when the parameters a and b vary, namely the equation of state. In particular, the critical dimension decreases when b decreases.


It is shown that for stars with radii in the range 2.25 GM/c 2 < R < ca . 3 GM/c 2 , quasi-normal axial modes of oscillation are possible. These modes are explicitly evaluated for stellar models of uniform energy density.


2021 ◽  
Vol 81 (6) ◽  
Author(s):  
Zdeněk Stuchlík ◽  
Jan Hladík ◽  
Jaroslav Vrba ◽  
Camilo Posada

AbstractExtremely compact objects trap gravitational waves or neutrinos, assumed to move along null geodesics in the trapping regions. The trapping of neutrinos was extensively studied for spherically symmetric extremely compact objects constructed under the simplest approximation of the uniform energy density distribution, with radius located under the photosphere of the external spacetime; in addition, uniform emissivity distribution of neutrinos was assumed in these studies. Here we extend the studies of the neutrino trapping for the case of the extremely compact Tolman VII objects representing the simplest generalization of the internal Schwarzschild solution with uniform distribution of the energy density, and the correspondingly related distribution of the neutrino emissivity that is thus again proportional to the energy density; radius of such extremely compact objects can overcome the photosphere of the external Schwarzschild spacetime. In dependence on the parameters of the Tolman VII spacetimes, we determine the “local” and “global” coefficients of efficiency of the trapping and demonstrate that the role of the trapping is significantly stronger than in the internal Schwarzschild spacetimes. Our results indicate possible influence of the neutrino trapping in cooling of neutron stars.


2020 ◽  
Vol 35 (32) ◽  
pp. 2050270
Author(s):  
Amir Ghalee

We present a new mechanism to condense a scalar field coupled to the Gauss–Bonnet term. We propose a scenario in which the condensed state will emerge from the background energy density in the late-Universe. During the radiation and dust-dominated eras, the energy density of the scalar field, [Formula: see text], decreases at a slower rate than the background density. Eventually, [Formula: see text] dominates over the energy density of dust and the scalar field could be condensed. In the condensed phase, we have the de Sitter phase for the universe with [Formula: see text]. Moreover, we study the cosmological perturbations of the model and explore predictions of the model.


2006 ◽  
Vol 21 (35) ◽  
pp. 2685-2701 ◽  
Author(s):  
CARLOS CASTRO

A class of proper and novel generalizations of the (anti) de Sitter solutions (parametrized by a family of radial functions R(r)) are presented that could provide a very plausible resolution of the cosmological constant problem along with a natural explanation of the ultraviolet/infrared (uv/ir) entanglement required to solve this problem. A nonvanishing value of the vacuum energy density of the order of [Formula: see text] is derived in agreement with the experimental observations. The presence of the radial function R(r) is instrumental to understand why the cosmological constant is not zero and why it is so tiny. The correct lower estimate of the mass of the observable universe related to the Dirac–Eddington's large number N = 1080 is also obtained. Finally we present our most recent findings of how Weyl Geometry via a Brans–Dicke scalar field solves the riddle of dark energy in addition to providing another derivation of the vacuum energy density.


2015 ◽  
Vol 2015 ◽  
pp. 1-7
Author(s):  
Jung-Jeng Huang

In Schrödinger picture we study the possible effects of trans-Planckian physics on the quantum evolution of massive nonminimally coupled scalar field in de Sitter space. For the nonlinear Corley-Jacobson type dispersion relations with quartic or sextic correction, we obtain the time evolution of the vacuum state wave functional during slow-roll inflation and calculate explicitly the corresponding expectation value of vacuum energy density. We find that the vacuum energy density is finite. For the usual dispersion parameter choice, the vacuum energy density for quartic correction to the dispersion relation is larger than for sextic correction, while for some other parameter choices, the vacuum energy density for quartic correction is smaller than for sextic correction. We also use the backreaction to constrain the magnitude of parameters in nonlinear dispersion relation and show how the cosmological constant depends on the parameters and the energy scale during the inflation at the grand unification phase transition.


2013 ◽  
Vol 2013 ◽  
pp. 1-7
Author(s):  
Pablo Alejandro Sánchez ◽  
Mauricio Bellini

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.


1973 ◽  
Vol 9 (6) ◽  
pp. 711-712 ◽  
Author(s):  
A. Bettinger ◽  
L. Jacob ◽  
C. Meunier ◽  
J. Pezot

2016 ◽  
Vol 2016 ◽  
pp. 1-8 ◽  
Author(s):  
Haidar Sheikhahmadi ◽  
Ali Aghamohammadi ◽  
Khaled Saaidi

During this work, using subtraction renormalization mechanism, zero point quantum fluctuations for bosonic scalar fields in a de-Sitter like background are investigated. By virtue of the observed value for spectral index,ns(k), for massive scalar field the best value for the first slow roll parameter,ϵ, is achieved. In addition, the energy density of vacuum quantum fluctuations for massless scalar field is obtained. The effects of these fluctuations on other components of the universe are studied. By solving the conservation equation, for some different examples, the energy density for different components of the universe is obtained. In the case which all components of the universe are in an interaction, the different dissipation functions,Q~i, are considered. The time evolution ofρDE(z)/ρcri(z)shows thatQ~=3γH(t)ρmhas the best agreement in comparison to observational data including CMB, BAO, and SNeIa data set.


2021 ◽  
Vol 4 (3) ◽  

The Cosmic Time Hypothesis (CTH) presented in this paper is a purely axiomatic theory. In contrast to today's standard model of cosmology, the ɅCDM model, it does not contain empirical parameters such as the cosmological constant Ʌ, nor does it contain sub-theories such as the inflation theory. The CTH was developed solely on the basis of the general theory of relativity (GRT), aiming for the greatest possible simplicity. The simplest cosmological model permitted by ART is the Einstein-de Sitter model. It is the basis for solving some of the fundamental problems of cosmology that concern us today. First of all, the most important results of the CTH: It solves one of the biggest problems of cosmology the problem of the cosmological constant (Ʌ)-by removing the relation between and the vacuum energy density ɛv (Λ=0, ɛv > 0). According to the CTH, the vacuum energy density ɛv is not negative and constant, as previously assumed, but positive and time-dependent (ɛv ̴ t -2). ɛv is part of the total energy density (Ɛ) of the universe and is contained in the energy-momentum tensor of Einstein's field equations. Cosmology is thus freed from unnecessary ballast, i.e. a free parameter (= natural constant) is omitted (Ʌ = 0). Conclusion: There is no "dark energy"! According to the CTH, the numerical value of the vacuum energy density v is smaller by a factor of ≈10-122 than the value calculated from quantum field theory and is thus consistent with observation. The measurement data obtained from observations of SNla supernovae, which suggest a currently accelerated expansion of the universe, result - if interpreted from the point of view of the CTH - in a decelerated expansion, as required by the Einstein-de Sitter universe. Dark matter could also possibly not exist, because the KZH demands that the "gravitational constant" is time-dependent and becomes larger the further the observed objects are spatially and thus also temporally distant from us. Gravitationally bound local systems, e.g. Earth - Moon or Sun - Earth, expand according to the same law as the universe. This explains why Hubble's law also applies within very small groups of galaxies, as observations show. The CTH requires that the strongest force (strong nuclear force) and the weakest (gravitational force) at Planck time (tp ≈10-43 seconds after the "big bang") when all forces of nature are supposed to have been united in a single super force, were of equal magnitude and had the same range. According to the KZH, the product of the strength and range of the gravitational force is constant, i.e. independent of time, and is identical to the product of the strength and range of the strong nuclear force. At Planck time, the universe had the size of an elementary particle (Rp = rE ≈10-15 m). This value also corresponds to the range of the strong nuclear force (Yukawa radius) and the Planck length at Planck time. The CTH provides a possible explanation for Mach's first and second principles. It solves some old problems of the big bang theory in a simple and natural way. The problem of the horizon, flatness, galaxy formation and the age of the world. The inflation theory thus becomes superfluous. • The CTH provides the theoretical basis for the theory of Earth expansion • In Cosmic Time, there was no Big Bang. The universe is infinitely old. • Unlike other cosmological models, the CTH does not require defined "initial conditions" because there was no beginning. • The CTH explains why the cosmic expansion is permanently in an unstable state of equilibrium, which is necessary for a long-term flat (Euclidean), evolutionarily developing universe.


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