scholarly journals Linear perturbations of the Linet - Tian metrics with apositive cosmological constant.

2021 ◽  
Author(s):  
Reinaldo J Gleiser
Keyword(s):  
Cosmological Constant ◽  
Linear Perturbations

scholarly journals AN ANALYTIC APPROACH TO THE LATE ISW EFFECT IN A Λ DOMINATED UNIVERSE

2005 ◽  
Vol 20 (30) ◽  
pp. 7233-7240 ◽  
Author(s):  
VIKTOR CZINNER ◽  
MÁTYÁS VASÚTH ◽  
ÁRPÁD LUKÁCS
Keyword(s):  
Power Spectrum ◽  
Cosmological Constant ◽  
Time Dependence ◽  
Ideal Fluid ◽  
Analytic Solution ◽  
Einstein Equations ◽  
Microwave Background ◽  
Frw Universe ◽  
Scale Invariant ◽  
Linear Perturbations

The integrated Sachs–Wolfe (ISW) effect in a Λ dominated universe can be an important factor in the evolution of cosmic microwave background fluctuations. With the inclusion of cosmological constant we present the complete analytic solution of the covariant linear perturbations of the Einstein equations in the Newtonian gauge, in the case of a spatially flat (K = 0), Friedman–Robertson–Walker (FRW) universe, filled with pressureless ideal fluid. We use the analytic time dependence of the perturbation potentials to derive the anisotropy power spectrum of the late ISW effect. We choose the scale invariant Harrison–Zeldovich spectrum for obtaining the Cℓ momenta and show the agreement of our results with earlier, numeric calculations.

scholarly journals The stability of self-accelerating Universe in modified gravity with dynamical torsion

2017 ◽  
Vol 32 (23n24) ◽  
pp. 1750137 ◽  
Author(s):  
Vasilisa Nikiforova
Keyword(s):  
Cosmological Constant ◽  
Modified Gravity ◽  
Degrees Of Freedom ◽  
The Self ◽  
Accelerating Universe ◽  
Effective Cosmological Constant ◽  
Linear Perturbations ◽  
The Stability ◽  
Scalar Sector ◽  
Rule Out

We consider the model of modified gravity with dynamical torsion. This model was previously found to have promising stability properties about various backgrounds. Here, we study the stability of linear perturbations about the self-accelerating solution. We apply the (3[Formula: see text]+[Formula: see text]1)-decomposition and consider the scalar sector of perturbations. We find that the number of degrees of freedom is equal to 2, which is the same as in Minkowski background. However, there is at least one instability in the scalar sector, if the value of background torsion is large enough. This does not rule out the possibility of stable self-acceleration with torsion of the order of the effective cosmological constant.

scholarly journals Primordial universe with the running cosmological constant

2020 ◽  
Vol 80 (9) ◽  
Author(s):  
Jhonny A. Agudelo Ruiz ◽  
Tibério de Paula Netto ◽  
Júlio C. Fabris ◽  
Ilya L. Shapiro
Keyword(s):  
Dark Matter ◽  
Cosmological Constant ◽  
Vacuum Energy ◽  
Vacuum Decay ◽  
Matter Power Spectrum ◽  
Cosmic Background ◽  
Linear Perturbations ◽  
The Impact ◽  
Best Fit ◽  
Matter Sector

AbstractTheoretically, the running of the cosmological constant in the IR region is not ruled out. On the other hand, from the QFT viewpoint, the energy released due to the variation of the cosmological constant in the late Universe cannot go to the matter sector. For this reason, the phenomenological bounds on such a running are not sufficiently restrictive. The situation can be different in the early Universe when the gravitational field was sufficiently strong to provide an efficient creation of particles from the vacuum. We develop a framework for systematically exploring this possibility. It is supposed that the running occurs in the epoch when the Dark Matter already decoupled and is expanding adiabatically, while the usual matter should be regarded approximately massless and can be abundantly created from vacuum due to the decay of vacuum energy. By using the handy model of Reduced Relativistic Gas for describing the warm Dark Matter, we consider the dynamics of both cosmic background and linear perturbations and evaluate the impact of the vacuum decay on the matter power spectrum and to the first CMB peak. Additionally, using the combined SNIa+BAO data, we find the best-fit values for the free parameters of the model.

scholarly journals COSMOLOGICAL PERTURBATIONS AND THE RUNNING COSMOLOGICAL CONSTANT MODEL

2012 ◽  
Vol 21 (03) ◽  
pp. 1250026 ◽  
Author(s):  
ALAN M. VELASQUEZ-TORIBIO
Keyword(s):  
Growth Rate ◽  
Cosmological Constant ◽  
Linear Growth ◽  
Characteristic Parameter ◽  
Density Fluctuations ◽  
Linear Growth Rate ◽  
Cluster Number ◽  
Matter Power Spectrum ◽  
Linear Perturbations ◽  
Standard Cosmological Model

We study the matter density fluctuations in the running cosmological constant (RCC) model using linear perturbations in the longitudinal gauge. Using this observable, we calculate the growth rate of structures and the matter power spectrum, and compare these results to SDSS data and the available data for linear growth rate. The distribution of collapsed structures may also constrain models of dark energy. It is shown that the RCC model enhances departures from the ΛCDM model for both cluster number and cumulative cluster number predicted. In general, increasing the characteristic parameter ν leads to significant growth of the cluster number. We found that the theory of perturbations provides a useful tool to distinguish between the new model RCC and the standard cosmological model ΛCDM.

Cosmological constant

2018 ◽  
Author(s):  
Michael Kachelriess
Keyword(s):  
Dark Energy ◽  
Cosmological Constant ◽  
Accelerated Expansion ◽  
Vacuum Fluctuations ◽  
Present Epoch ◽  
Modify Gravity ◽  
Expansion Of The Universe ◽  
The Universe

The contribution of vacuum fluctuations to the cosmological constant is reconsidered studying the dependence on the used regularisation scheme. Then alternative explanations for the observed accelerated expansion of the universe in the present epoch are introduced which either modify gravity or add a new component of matter, dubbed dark energy. The chapter closes with some comments on attempts to quantise gravity.

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