scholarly journals Big bounce with finite-time singularity: The F(R) gravity description

2017 ◽  
Vol 26 (08) ◽  
pp. 1750085 ◽  
Author(s):  
S. D. Odintsov ◽  
V. K. Oikonomou
Keyword(s):  
Big Bang ◽  
Einstein Frame ◽  
Jordan Frame ◽  
Cosmological Perturbations ◽  
Scale Invariant ◽  
Type Iv ◽  
Big Rip ◽  
Cosmological Scenario ◽  
The Big Bang ◽  
Big Bounce

An alternative to the Big Bang cosmologies is obtained by the Big Bounce cosmologies. In this paper, we study a bounce cosmology with a Type IV singularity occurring at the bouncing point in the context of [Formula: see text] modified gravity. We investigate the evolution of the Hubble radius and we examine the issue of primordial cosmological perturbations in detail. As we demonstrate, for the singular bounce, the primordial perturbations originating from the cosmological era near the bounce do not produce a scale-invariant spectrum and also the short wavelength modes after these exit the horizon, do not freeze, but grow linearly with time. After presenting the cosmological perturbations study, we discuss the viability of the singular bounce model, and our results indicate that the singular bounce must be combined with another cosmological scenario, or should be modified appropriately, in order that it leads to a viable cosmology. The study of the slow-roll parameters leads to the same result indicating that the singular bounce theory is unstable at the singularity point for certain values of the parameters. We also conformally transform the Jordan frame singular bounce, and as we demonstrate, the Einstein frame metric leads to a Big Rip singularity. Therefore, the Type IV singularity in the Jordan frame becomes a Big Rip singularity in the Einstein frame. Finally, we briefly study a generalized singular cosmological model, which contains two Type IV singularities, with quite appealing features.

scholarly journals Measurement and Implications of the Cosmic Microwave Background Spectrum

1996 ◽  
Vol 168 ◽  
pp. 17-29
Author(s):  
John C. Mather
Keyword(s):  
Background Radiation ◽  
Far Infrared ◽  
Big Bang ◽  
Scale Invariant ◽  
Background Spectrum ◽  
Nasa Goddard Space ◽  
Wide Range ◽  
Infrared Background ◽  
Microwave Radiometers ◽  
The Big Bang

The Cosmic Background Explorer (COBE) was developed by NASA Goddard Space Flight Center to measure the diffuse infrared and microwave radiation from the early universe. It also measured emission from nearby sources such as the stars, dust, molecules, atoms, ions, and electrons in the Milky Way, and dust and comets in the Solar System. It was launched 18 November 1989 on a Delta rocket, carrying one microwave instrument and two cryogenically cooled infrared instruments. The Far Infrared Absolute Spectrophotometer (FIRAS) mapped the sky at wavelengths from 0.01 to 1 cm, and compared the CMBR to a precise blackbody. The spectrum of the CMBR differs from a blackbody by less than 0.03%. The Differential Microwave Radiometers (DMR) measured the fluctuations in the CMBR originating in the Big Bang, with a total amplitude of 11 parts per million on a 10° scale. These fluctuations are consistent with scale-invariant primordial fluctuations. The Diffuse Infrared Background Experiment (DIRBE) spanned the wavelength range from 1.2 to 240 μm and mapped the sky at a wide range of solar elongation angles to distinguish foreground sources from a possible extragalactic Cosmic Infrared Background Radiation (CIBR). In this paper we summarize the COBE mission and describe the results from the FIRAS instrument. The results from the DMR and DIRBE were described by Smoot and Hauser at this Symposium.

scholarly journals Quantization of time and the big bang via scale-invariant loop gravity

2020 ◽  
Vol 800 ◽  
pp. 135106
Author(s):  
Charles H.-T. Wang ◽  
Marcin Stankiewicz
Keyword(s):  
Big Bang ◽  
Scale Invariant ◽  
The Big Bang ◽  
Loop Gravity

scholarly journals Cosmology at the top of the α′ tower

2021 ◽  
Vol 2021 (7) ◽  
Author(s):  
Jerome Quintin ◽  
Heliudson Bernardo ◽  
Guilherme Franzmann
Keyword(s):  
Energy Condition ◽  
Big Bang ◽  
Null Energy Condition ◽  
Einstein Frame ◽  
Accelerated Expansion ◽  
De Sitter ◽  
The Big Bang ◽  
Big Bang Singularity ◽  
Matter Sector

Abstract The cosmology of the fully α′-corrected duality-invariant action for the Neveu-Schwarz sector of string theory is revisited, with special emphasis on its coupling to matter sources. The role of the duality covariant pressure and dilatonic charge of the matter sector is explored in various contexts, from the low-curvature regime to non-perturbative solutions in α′. We comment on how an infinite tower of α′ corrections allows for fixed-dilaton de Sitter solutions, even in vacuum. We further investigate the necessary conditions for accelerated expansion in the Einstein frame, as well as for non-singular bounces that could resolve the big bang singularity. In particular, explicit examples are constructed, which show that the tower of α′ corrections may support an Einstein-frame non-singular cosmological bouncing background, even when the matter sector respects the null energy condition.

scholarly journals On Gauge Invariant Cosmological Perturbations in UV-modified Hořava Gravity: A Brief Introduction

2018 ◽  
Vol 168 ◽  
pp. 08003 ◽  
Author(s):  
Mu-In Park
Keyword(s):  
Detailed Balance ◽  
Big Bang ◽  
Matter Field ◽  
Cosmological Perturbations ◽  
Scale Invariant ◽  
Gauge Invariant ◽  
Four Dimensions ◽  
Detailed Balance Condition ◽  
Scalar Matter ◽  
Horava Gravity

We revisit gauge invariant cosmological perturbations in UV-modified, z = 3 Hořava gravity with one scalar matter field, which has been proposed as a renormalizable gravity theory without the ghost problem in four dimensions. We confirm that there is no extra graviton modes and general relativity is recovered in IR, which achieves the consistency of the model. From the UV-modification terms which break the detailed balance condition in UV, we obtain scale-invariant power spectrums for non-inflationary backgrounds, like the power-law expansions, without knowing the details of early expansion history of Universe. This could provide a new framework for the Big Bang cosmology.

scholarly journals The Solution of the Cosmological Constant Problem: The Cosmological Constant Exponential Decrease in the Super-Early Universe

Universe ◽  
2020 ◽  
Vol 6 (12) ◽  
pp. 230
Author(s):  
Ol’ga Babourova ◽  
Boris Frolov
Keyword(s):  
Cosmological Constant ◽  
Big Bang ◽  
Cosmological Constant Problem ◽  
Scale Invariant ◽  
Weyl Space ◽  
Effective Cosmological Constant ◽  
Exponential Decrease ◽  
The Big Bang ◽  
Modern Era ◽  
Gauge Theory Of Gravity

The stage of a super-early (primordial) scale-invariant Universe is considered on the basis of the Poincaré–Weyl gauge theory of gravity in a Cartan–Weyl space-time. An approximate solution has been found that demonstrates an inflationary behavior of the scale factor and, at the same time, a sharp exponential decrease in the effective cosmological constant from a huge value at the beginning of the Big Bang to an extremely small (but not zero) value in the modern era, which solves the well-known “cosmological constant problem.”

scholarly journals REALISTIC CYCLIC MAGNETIC UNIVERSE

2012 ◽  
Vol 21 (09) ◽  
pp. 1250073 ◽  
Author(s):  
L. G. MEDEIROS
Keyword(s):  
Magnetic Field ◽  
Big Bang ◽  
Nonlinear Electrodynamics ◽  
Baryonic Matter ◽  
Big Rip ◽  
Cosmological Scenario ◽  
Free Parameters ◽  
Big Bang Model ◽  
Theoretical Considerations ◽  
The Magnetic Field

This work presents a complete cyclic cosmological scenario based on nonlinear magnetic field. It is constructed from a model composed of five fluids, namely baryonic matter, dark matter, radiation, neutrinos and a cosmological magnetic field. The first four fluids are treated in the standard way and the fifth fluid, the magnetic field, is described by a nonlinear electrodynamics. The free parameters are fitted by observational data (SNIa, CMB, extragalactic magnetic fields, etc.) and by simple theoretical considerations. As a result arises a cyclic cosmological model that preserves the main successes of the standard Big Bang model and solves some other problems such as the initial singularity, the present acceleration and the Big Rip.

A holographic big bang?

2015 ◽  
Vol 24 (12) ◽  
pp. 1544029
Author(s):  
N. Afshordi ◽  
R. B. Mann ◽  
R. Pourhasan
Keyword(s):  
Cosmological Model ◽  
Big Bang ◽  
Initial Singularity ◽  
Scale Invariant ◽  
The Big Bang ◽  
The Universe ◽  
Important Test

We present a cosmological model in which the Universe emerges out of the collapse of a five-dimensional (5D) star as a spherical three-brane. The initial singularity of the big bang becomes hidden behind a causal horizon. Near scale-invariant primordial curvature perturbations can be induced on the brane via a thermal atmosphere that is in equilibrium with the brane, circumventing the need for a separate inflationary process and providing an important test of the model.

scholarly journals Gravity as the breakdown of conformal invariance

2015 ◽  
Vol 24 (12) ◽  
pp. 1543002 ◽  
Author(s):  
Giovanni Amelino-Camelia ◽  
Michele Arzano ◽  
Giulia Gubitosi ◽  
João Magueijo
Keyword(s):  
Gravity Waves ◽  
Conformal Invariance ◽  
Scale Invariance ◽  
Big Bang ◽  
Two Dimensional ◽  
Top Down ◽  
Scale Invariant ◽  
Primordial Power Spectrum ◽  
The Big Bang ◽  
The Universe

In this paper, we propose that at the beginning of the universe gravity existed in a limbo either because it was switched off or because it was only conformally coupled to all particles. This picture can be reverse-engineered from the requirement that the cosmological perturbations be (nearly) scale-invariant without the need for inflation. It also finds support in recent results in quantum gravity suggesting that spacetime becomes two-dimensional at super-Planckian energies. We advocate a novel top-down approach to cosmology based on the idea that gravity and the Big Bang Universe are relics from the mechanism responsible for breaking the fundamental conformal invariance. Such a mechanism should leave clear signatures in departures from scale-invariance in the primordial power spectrum and the level of gravity waves generated.

scholarly journals The Solution of the Cosmological Constant Problem: The Cosmological Constant Exponential Decrease in the Super-Early Universe

2020 ◽  
Author(s):  
Ol'ga Babourova ◽  
Boris Frolov
Keyword(s):  
Cosmological Constant ◽  
Big Bang ◽  
Cosmological Constant Problem ◽  
Scale Invariant ◽  
Weyl Space ◽  
Effective Cosmological Constant ◽  
Exponential Decrease ◽  
The Big Bang ◽  
Modern Era ◽  
Gauge Theory Of Gravity

The stage of a super-early scale-invariant Universe is considered on the basis of the Poincaré–Weyl gauge theory of gravity in a Cartan–Weyl space-time. An approximate solution has been found that demonstrates an inflationary behavior of the scale factor and, at the same time, a sharp exponential decrease in the effective cosmological constant from a huge value at the beginning of the Big Bang to an extremely small (but not zero) value in the modern era, which solves the well-known “cosmological constant problem”.

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