Gravitational waves: A probe to the physics in the early universe

2015 ◽  
Vol 30 (28n29) ◽  
pp. 1545005
Author(s):  
Qing-Guo Huang
Keyword(s):  
Quantum Theory ◽  
Gravitational Waves ◽  
Early Universe ◽  
Upper Bound ◽  
Planck Scale ◽  
Big Bang ◽  
Planck Data ◽  
Inflationary Scenario ◽  
Fundamental Scale ◽  
The Big Bang

Gravitational waves can escape from the big bang and can be taken as a probe to the physics, in particular the inflation, in the early universe. Planck scale is a fundamental scale for quantum theory of gravity. Requiring the excursion distance of inflaton in the field space during inflation yields an upper bound on the tensor-to-scalar ratio. For example, [Formula: see text] for [Formula: see text]. In the typical inflationary scenario, we predict [Formula: see text] and [Formula: see text] which are consistent with Planck data released in 2015 quite well. Subtracting the contribution of thermal dust measured by Planck, BICEP2 data implies [Formula: see text] which is the tightest bound on the tensor-to-scalar ratio from current experiments.

scholarly journals Relativistic Cosmology with an Introduction to Inflation

Universe ◽  
2021 ◽  
Vol 7 (8) ◽  
pp. 276
Author(s):  
Muhammad Zahid Mughal ◽  
Iftikhar Ahmad ◽  
Juan Luis García Guirao
Keyword(s):  
Standard Model ◽  
Early Universe ◽  
Large Scale ◽  
Initial Conditions ◽  
Big Bang ◽  
Relativistic Cosmology ◽  
The Standard Model ◽  
Big Bang Model ◽  
The Big Bang ◽  
The Universe

In this review article, the study of the development of relativistic cosmology and the introduction of inflation in it as an exponentially expanding early phase of the universe is carried out. We study the properties of the standard cosmological model developed in the framework of relativistic cosmology and the geometric structure of spacetime connected coherently with it. The geometric properties of space and spacetime ingrained into the standard model of cosmology are investigated in addition. The big bang model of the beginning of the universe is based on the standard model which succumbed to failure in explaining the flatness and the large-scale homogeneity of the universe as demonstrated by observational evidence. These cosmological problems were resolved by introducing a brief acceleratedly expanding phase in the very early universe known as inflation. The cosmic inflation by setting the initial conditions of the standard big bang model resolves these problems of the theory. We discuss how the inflationary paradigm solves these problems by proposing the fast expansion period in the early universe. Further inflation and dark energy in fR modified gravity are also reviewed.

scholarly journals Phenomenological Implications of Modified Loop Cosmologies: An Overview

2021 ◽  
Vol 8 ◽  
Author(s):  
Bao-Fei Li ◽  
Parampreet Singh ◽  
Anzhong Wang
Keyword(s):  
Initial Conditions ◽  
Scale Effects ◽  
Hybrid Approach ◽  
Planck Scale ◽  
Power Spectra ◽  
Big Bang ◽  
Hamiltonian Constraint ◽  
Hybrid Approaches ◽  
Effective Dynamics ◽  
The Big Bang

In this paper, we first provide a brief review of the effective dynamics of two recently well-studied models of modified loop quantum cosmologies (mLQCs), which arise from different regularizations of the Hamiltonian constraint and show the robustness of a generic resolution of the big bang singularity, replaced by a quantum bounce due to non-perturbative Planck scale effects. As in loop quantum cosmology (LQC), in these modified models the slow-roll inflation happens generically. We consider the cosmological perturbations following the dressed and hybrid approaches and clarify some subtle issues regarding the ambiguity of the extension of the effective potential of the scalar perturbations across the quantum bounce, and the choice of initial conditions. Both of the modified regularizations yield primordial power spectra that are consistent with current observations for the Starobinsky potential within the framework of either the dressed or the hybrid approach. But differences in primordial power spectra are identified among the mLQCs and LQC. In addition, for mLQC-I, striking differences arise between the dressed and hybrid approaches in the infrared and oscillatory regimes. While the differences between the two modified models can be attributed to differences in the Planck scale physics, the permissible choices of the initial conditions and the differences between the two perturbation approaches have been reported for the first time. All these differences, due to either the different regularizations or the different perturbation approaches in principle can be observed in terms of non-Gaussianities.

scholarly journals The holographic spacetime model of cosmology

2018 ◽  
Vol 27 (14) ◽  
pp. 1846005 ◽  
Author(s):  
Tom Banks ◽  
W. Fischler
Keyword(s):  
Dark Matter ◽  
Gravitational Waves ◽  
Structure Formation ◽  
Big Bang ◽  
Baryon Asymmetry ◽  
Gaussian Fluctuations ◽  
Primordial Gravitational Waves ◽  
Conventional Models ◽  
Non Gaussian ◽  
The Big Bang

This essay outlines the Holographic Spacetime (HST) theory of cosmology and its relation to conventional theories of inflation. The predictions of the theory are compatible with observations, and one must hope for data on primordial gravitational waves or non-Gaussian fluctuations to distinguish it from conventional models. The model predicts an early era of structure formation, prior to the Big Bang. Understanding the fate of those structures requires complicated simulations that have not yet been done. The result of those calculations might falsify the model, or might provide a very economical framework for explaining dark matter and the generation of the baryon asymmetry.

The First Stars

2013 ◽  
Author(s):  
Abraham Loeb ◽  
Steven R. Furlanetto
Keyword(s):  
Phase Transition ◽  
Early Universe ◽  
Galaxy Formation ◽  
Big Bang ◽  
First Stars ◽  
Complex Chemical ◽  
Radiative Processes ◽  
Complex Processes ◽  
The Big Bang ◽  
The Universe

This chapter considers the emergence of the complex chemical and radiative processes during the first stages of galaxy formation. It studies the appearance of the first stars, their feedback processes, and the resulting ionization structures that emerged during and shortly after the cosmic dawn. The formation of the first stars tens or hundreds of millions of years after the Big Bang had marked a crucial transition in the early Universe. Before this point, the Universe was elegantly described by a small number of parameters. But as soon as the first stars formed, more complex processes entered the scene. To illustrate this, the chapter provides a brief outline of the prevailing (though observationally untested) theory for this cosmological phase transition.

Relativistic Theory of the Behavior of Irregularities in an Expanding World Model

2020 ◽  
pp. 304-378
Author(s):  
P. J. E. Peebles
Keyword(s):  
Early Universe ◽  
Relativistic Theory ◽  
Inertial Mass ◽  
Big Bang ◽  
Causal Connection ◽  
The Mean ◽  
Homogeneous Background ◽  
The Big Bang ◽  
The Universe ◽  
Relativistic Analysis

This chapter presents the full relativistic analysis of the evolution of mass clustering. The full relativistic theory is needed to deal with three important aspects of density irregularities in the early universe. First, when the pressure is high the relativistic active gravitational mass and inertial mass associated with pressure affect the dynamics. Second, when the mean density is high, a fluctuation of even modest fractional amount containing a modest mass can have a large effect on the space curvature. One is thus led to deal with the interaction of speculations on the nature of the mass distribution and of the geometry in the early universe. Third, the horizon shrinks to zero at the time of the big bang: the seed fluctuations out of which galaxies might form were larger than the horizon and so were not in causal connection reckoned from the time of the big bang. Of course, this curious point applies as well to the homogeneous background: it was somehow contrived that all parts of the universe now visible were set expanding with quite precise uniformity even though an observer could not have discovered this much before the present epoch.

scholarly journals Quasi-Steady State Cosmology

1994 ◽  
Vol 159 ◽  
pp. 293-299
Author(s):  
G. Burbidge ◽  
F. Hoyle ◽  
J.V. Narlikar
Keyword(s):  
Steady State ◽  
Early Universe ◽  
Particle Physics ◽  
Physical Theory ◽  
Big Bang ◽  
Quasi Steady State ◽  
Recent Developments ◽  
History Of ◽  
The Big Bang ◽  
The Universe

The standard big bang cosmology has the universe created out of a primeval explosion that not only created matter and radiation but also spacetime itself. The big bang event itself cannot be discussed within the framework of a physical theory but the events following it are in principle considered within the scope of science. The recent developments on the frontier between particle physics and cosmology highlight the attempts to chart the history of the very early universe.

Gravitational waves from the big bang

1980 ◽  
Vol 29 (16) ◽  
pp. 528-532
Author(s):  
A. Qadir ◽  
A. A. Mufti
Keyword(s):  
Gravitational Waves ◽  
Big Bang ◽  
The Big Bang

First stars, hypernovae, and superluminous supernovae

2016 ◽  
Vol 25 (10) ◽  
pp. 1630025
Author(s):  
Ken’ichi Nomoto
Keyword(s):  
Early Universe ◽  
Big Bang ◽  
Elemental Abundance ◽  
Heavy Elements ◽  
Relativistic Jets ◽  
First Stars ◽  
Evolution Of Galaxies ◽  
Abundance Patterns ◽  
The Big Bang

After the big bang, production of heavy elements in the early universe takes place starting from the formation of the first (Pop III) stars, their evolution, and explosion. The Pop III supernova (SN) explosions have strong dynamical, thermal, and chemical feedback on the formation of subsequent stars and evolution of galaxies. However, the nature of Pop III stars/supernovae (SNe) have not been well-understood. The signature of nucleosynthesis yields of the first SN can be seen in the elemental abundance patterns observed in extremely metal-poor (EMP) stars. We show that the abundance patterns of EMP stars, e.g. the excess of C, Co, Zn relative to Fe, are in better agreement with the yields of hyper-energetic explosions (Hypernovae, (HNe)) rather than normal supernovae. We note the large variation of the abundance patterns of EMP stars propose that such a variation is related to the diversity of the GRB-SNe and posssibly superluminous supernovae (SLSNe). For example, the carbon-enhanced metal-poor (CEMP) stars may be related to the faint SNe (or dark HNe), which could be the explosions induced by relativistic jets. Finally, we examine the various mechanisms of SLSNe.

The early universe in a generalized theory of gravitation

1982 ◽  
Vol 60 (5) ◽  
pp. 659-663 ◽  
Author(s):  
J. W. Moffat ◽  
D. Vincent
Keyword(s):  
Early Universe ◽  
Initial Conditions ◽  
Big Bang ◽  
Field Equations ◽  
Anisotropic Solution ◽  
Plane Symmetric ◽  
Frw Model ◽  
Theory Of Gravitation ◽  
The Big Bang ◽  
The Universe

The standard Friedmann–Robertson–Walker (FRW) big-bang model of the universe requires special initial conditions: the early universe is highly homogeneous and isotropic even though there exist causally disconnected regions (horizon problem). A plane symmetric (anisotropic) solution of a system of field equations in a generalized theory of gravitation, predicts the beginning of the universe as a vacuum instability at a specific fundamental time (which can be associated with the Planck time (tp)), after which matter is created as the universe begins to expand. At a time t = tc there is a singular expansion, the anisotropy vanishes, and the physical horizon becomes infinite. Thereafter the solution of the field equations goes over into the FRW model. Thus the special initial conditions of the FRW model at the big-bang singularity t = tc are predicted by the theory.

scholarly journals Temporal (t > 0) Space and Gravitational Waves

2021 ◽  
Author(s):  
Francis T.S. Yu
Keyword(s):  
Gravitational Waves ◽  
Empty Space ◽  
Big Bang ◽  
Gravitational Energy ◽  
Induced Gravity ◽  
Temporal Space ◽  
Time Space ◽  
The Big Bang ◽  
Gravitation Force ◽  
Over Time

I will begin with the nature of our temporal (t > 0) universe, since without temporal space there would be no gravitation force because gravitational field cannot be created within an empty space. When we are dealing with physical realizability of science, Einstein’s relativity theories cannot be ignored since relativistic mechanics is dealing with very large objects. Nevertheless I will show that huge gravitational waves can be created by a gigantic mass annihilation only within a temporal (t > 0) space. Since gravitational energy has never been consider as a significant component within big bang creation, I will show it is a key component to ignite the big bang explosion, contrary to commonly believed that big bang explosion was ignited by time. I will show a huge gravitation energy reservoir induced by a gigantic mass had had been created over time well before the big bang started. Since the assumed singularity mass within a temporal (t > 0) had had gotten heavier and heavier similar to a gigantic black hole that continuingly swallows up huge chunk of substances within the space. From which we see that it is the gravitational force that triggers the thermo-nuclei big bang creation, instead ignited by time as postulated. Aside the thermo-nuclei creation, it had a gigantic gravitational wave release as mass annihilates rapidly by big bang explosion. From which we see that it is the induced gravitational reservoir changes with time, but not the induced gravity changes (i.e., curves) time–space. In other words if there has no temporal (t > 0) space then there will be no gravitational waves.

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