Late-time behavior of primordial gravitational waves in expanding universe

1988 ◽  
Vol 20 (2) ◽  
pp. 183-190 ◽  
Author(s):  
Alexander Feinstein
Keyword(s):  
Gravitational Waves ◽  
Late Time ◽  
Time Behavior ◽  
Expanding Universe ◽  
Primordial Gravitational Waves

Interacting dark energy models in f(T) gravity

2017 ◽  
Vol 32 (18) ◽  
pp. 1750097 ◽  
Author(s):  
M. Khurshudyan ◽  
R. Myrzakulov ◽  
As. Khurshudyan
Keyword(s):  
Phase Transition ◽  
Observational Data ◽  
Large Scale ◽  
Cosmological Models ◽  
Accelerated Expansion ◽  
Late Time ◽  
Time Behavior ◽  
Expanding Universe ◽  
Theory Of Gravity ◽  
Large Scale Universe

The accelerated expansion of the large-scale universe can be explained in various ways. There are various modifications, and each of them makes an attempt to give its own explanation of the physics behind it. It is well known that modern cosmology is full of various phenomenological assumptions to obtain comprehensive results comparable with observational data. General Relativity is the main theory of gravity and proposed modifications compared to it, giving a hope to find explanations of phenomenological assumptions. f(T) theory of gravity is one of the options. In this paper, we will consider a particular example of f(T) theory and study the effects of various interactions on a cosmological model. Phase space analysis is used to have a qualitative understanding of the late-time behavior of the suggested cosmological models. During our study, we found that among phenomenological models suggested in this paper, we have cosmological models being in good agreement with the observational data. Moreover, study of the behavior of the deceleration parameter q showed a phase transition from a decelerated expanding universe to the accelerated (recent) expanding universe. On the other hand, for the parameters of the models giving the mentioned phase transition, we have estimated the present day values of statefinder parameters (r, s).

scholarly journals Decoding the phases of early and late time reheating through imprints on primordial gravitational waves

2021 ◽  
Vol 104 (6) ◽  
Author(s):  
Md Riajul Haque ◽  
Debaprasad Maity ◽  
Tanmoy Paul ◽  
L. Sriramkumar
Keyword(s):  
Gravitational Waves ◽  
Late Time ◽  
Primordial Gravitational Waves

scholarly journals On the Present Time Approximate Values of the Characteristic Parameters of the Primordial Gravitational Waves

2003 ◽  
Vol 214 ◽  
pp. 376-381
Author(s):  
M. Melek
Keyword(s):  
Temporal Variation ◽  
Gravitational Waves ◽  
Conventional Approach ◽  
Expanding Universe ◽  
Characteristic Parameters ◽  
Spectral Densities ◽  
Frw Universe ◽  
Frequency Bands ◽  
Future Networks ◽  
Primordial Gravitational Waves

An approach is used to find out the present time approximate values of the characteristic amplitudes, the spectral densities, the intensties and the frequencies of the Primordial Gravitational Waves (PmGW), in the spatially perturbed Friedman - Robertson - Walker (FRW) adiabatically expanding Universe. The temporal variation of the magnitude of the time gradient of the characteristic amplitudes of the PmGW is calculated in spatial perturbed FRW Universe. The obtained results via this non-conventional approach may be of interest to shed some light on the possibilities of searching for the PmGW at definite frequency bands by the existing and the future networks of detectors.

scholarly journals Fluctuations in the Microwave Background Caused by Anisotropy of the Universe and Gravitational Waves

1977 ◽  
Vol 74 ◽  
pp. 335-339
Author(s):  
I. D. Novikov
Keyword(s):  
Gravitational Waves ◽  
Galaxy Formation ◽  
Expanding Universe ◽  
Microwave Background ◽  
Primordial Gravitational Waves ◽  
Order Of Magnitude ◽  
Density Perturbations ◽  
The Universe

The problem described in the title has already been theoretically analysed several times (see for example Dautcourt, 1969 and Novikov, 1974). Recently, however some important new aspects of the problem have been discovered; they are discussed briefly in this report which is based upon the calculations of Doroshkevich, Lukash, Novikov and Polnarev. First consider the influence of primordial gravitational waves on the microwave background. It is natural to assume that in the Universe, in addition to acoustic (or adiabatic) density perturbations which result in galaxy formation and corresponding metric perturbations, there also exist metric perturbations in the form of gravitational waves with wavelengths of the same order of magnitude as the acoustic perturbations. The amplitude of such gravitational waves could in principle be quite arbitrary. Their amplitude can be estimated by comparing the theory of such waves in the expanding Universe with the observed fluctuations in the microwave background which are now available or will be in future.

scholarly journals Late Time Attractors of Some Varying Chaplygin Gas Cosmological Models

Symmetry ◽  
2021 ◽  
Vol 13 (5) ◽  
pp. 769
Author(s):  
Martiros Khurshudyan ◽  
Ratbay Myrzakulov
Keyword(s):  
Dark Energy ◽  
Gravitational Interaction ◽  
Chaplygin Gas ◽  
Cosmological Models ◽  
Late Time ◽  
Time Behavior ◽  
Coincidence Problem ◽  
Energy Models ◽  
Non Linear ◽  
Bayesian Machine Learning

The goal of this paper is to study new cosmological models where the dark energy is a varying Chaplygin gas. This specific dark energy model with non-linear EoS had been often discussed in modern cosmology. Contrary to previous studies, we consider new forms of non-linear non-gravitational interaction between dark matter and assumed dark energy models. We applied the phase space analysis allowing understanding the late time behavior of the models. It allows demonstrating that considered non-gravitational interactions can solve the cosmological coincidence problem. On the other hand, we applied Bayesian Machine Learning technique to learn the constraints on the free parameters. In this way, we gained a better understanding of the models providing a hint which of them can be ruled out. Moreover, the learning based on the simulated expansion rate data shows that the models cannot solve the H0 tension problem.

scholarly journals Probing primordial gravitational waves: Ali CMB Polarization Telescope

2018 ◽  
Vol 6 (1) ◽  
pp. 145-154 ◽  
Author(s):  
Hong Li ◽  
Si-Yu Li ◽  
Yang Liu ◽  
Yong-Ping Li ◽  
Yifu Cai ◽  
...  
Keyword(s):  
Gravitational Waves ◽  
High Energy Physics ◽  
Transition Edge Sensor ◽  
High Energy ◽  
Cpt Symmetry ◽  
Joint Project ◽  
Current Limit ◽  
Scientific Goal ◽  
Primordial Gravitational Waves ◽  
Cmb Polarization

Abstract In this paper, we will give a general introduction to the Ali CMB Polarization Telescope (AliCPT) project, which is a Sino–US joint project led by the Institute of High Energy Physics and involves many different institutes in China. It is the first ground-based Cosmic Microwave Background (CMB) polarization experiment in China and an integral part of China's Gravitational-wave Program. The main scientific goal of the AliCPT project is to probe the primordial gravitational waves (PGWs) originating from the very early Universe. The AliCPT project includes two stages. The first stage, referred to as AliCPT-1, is to build a telescope in the Ali region of Tibet at an altitude of 5250 meters. Once completed, it will be the highest ground-based CMB observatory in the world and will open a new window for probing PGWs in the northern hemisphere. The AliCPT-1 telescope is designed to have about 7000 transition-edge sensor detectors at 95 GHz and 150 GHz. The second stage is to have a more sensitive telescope (AliCPT-2) with more than 20 000 detectors. Our simulations show that AliCPT will improve the current constraint on the tensor-to-scalar ratio r by one order of magnitude with three years' observation. Besides the PGWs, AliCPT will also enable a precise measurement of the CMB rotation angle and provide a precise test of the CPT symmetry. We show that three years' observation will improve the current limit by two orders of magnitude.

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