scholarly journals A BACK-REACTION INDUCED LOWER BOUND ON THE TENSOR-TO-SCALAR RATIO

2008 ◽  
Vol 23 (10) ◽  
pp. 727-735 ◽  
Author(s):  
PATRICK MARTINEAU ◽  
ROBERT BRANDENBERGER
Keyword(s):  
Lower Bound ◽  
Gravitational Waves ◽  
Power Spectra ◽  
Back Reaction ◽  
Scale Invariant ◽  
Large Classes ◽  
Higher Order Terms ◽  
Scalar Amplitude ◽  
Inflationary Models ◽  
Metric Fluctuations

There are large classes of inflationary models, particularly popular in the context of string theory and braneworld approaches to inflation, in which the ratio of linearized tensor-to-scalar metric fluctuations is very small. In such models, however, gravitational waves produced by scalar modes cannot be neglected. We derive the lower bound on the tensor-to-scalar ratio by considering the back-reaction of the scalar perturbations as a source of gravitational waves. These results show that no cosmological model that is compatible with a metric scalar amplitude of ≈10-5 can have a ratio of the tensor-to-scalar power spectra less than ≈10-8 at recombination and that higher-order terms leads to logarithmic growth for r during radiation domination. Our lower bound also applies to non-inflationary models which produce an almost scale-invariant spectrum of coherent super-Hubble scale metric fluctuations.

scholarly journals STRING GAS COSMOLOGY AND STRUCTURE FORMATION

2007 ◽  
Vol 22 (21) ◽  
pp. 3621-3642 ◽  
Author(s):  
ROBERT H. BRANDENBERGER ◽  
ALI NAYERI ◽  
SUBODH P. PATIL ◽  
CUMRUN VAFA
Keyword(s):  
Gravitational Waves ◽  
Structure Formation ◽  
Causal Mechanism ◽  
De Sitter ◽  
Scale Invariant ◽  
String Gas Cosmology ◽  
Metric Fluctuations

It has recently been shown that a Hagedorn phase of string gas cosmology may provide a causal mechanism for generating a nearly scale-invariant spectrum of scalar metric fluctuations, without the need for an intervening period of de Sitter expansion. A distinctive signature of this structure formation scenario would be a slight blue tilt of the spectrum of gravitational waves. In this paper we give more details of the computations leading to these results, and the assumptions underlying them.

On Primordial Black Holes and secondary gravitational waves generated from inflation with solo/multi-bumpy potential

2021 ◽  
Author(s):  
Rui feng Zheng ◽  
Jia ming Shi ◽  
Taotao Qiu
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Gravitational Waves ◽  
Power Spectra ◽  
Small Scale ◽  
Primordial Black Hole ◽  
Primordial Black Holes ◽  
Slow Roll ◽  
Spherical Collapse ◽  
Scalar Perturbations

Abstract It is well known that primordial black hole (PBH) can be generated in inflation process of the early universe, especially when the inflaton field has some non-trivial features that could break the slow-roll condition. In this paper, we investigate a toy model of inflation with bumpy potential, which has one or several bumps. We found that potential with multi-bump can give rise to power spectra with multi peaks in small-scale region, which can in turn predict the generation of primordial black holes in various mass ranges. We also consider the two possibilities of PBH formation by spherical collapse and elliptical collapse. And discusses the scalar-induced gravitational waves (SIGWs) generated by the second-order scalar perturbations.

scholarly journals Power spectra of random spike fields and related processes

2005 ◽  
Vol 37 (4) ◽  
pp. 1116-1146 ◽  
Author(s):  
Pierre Brémaud ◽  
Laurent Massoulié ◽  
Andrea Ridolfi
Keyword(s):  
Point Process ◽  
Point Processes ◽  
Power Spectra ◽  
Sampling Point ◽  
Birth And Death Processes ◽  
Large Classes ◽  
Random Samples ◽  
Branching Point ◽  
Random Times ◽  
Random Impulse

In this article, we review known results and present new ones concerning the power spectra of large classes of signals and random fields driven by an underlying point process, such as spatial shot noises (with random impulse response and arbitrary basic stationary point processes described by their Bartlett spectra) and signals or fields sampled at random times or points (where the sampling point process is again quite general). We also obtain the Bartlett spectrum for the general linear Hawkes spatial branching point process (with random fertility rate and general immigrant process described by its Bartlett spectrum). We then obtain the Bochner spectra of general spatial linear birth and death processes. Finally, we address the issues of random sampling and linear reconstruction of a signal from its random samples, reviewing and extending former results.

scholarly journals SPECTRA OF RELIC GRAVITONS AND BRANS–DICKE THEORY

2005 ◽  
Vol 20 (02) ◽  
pp. 127-134 ◽  
Author(s):  
B. K. SAHOO
Keyword(s):  
Scalar Field ◽  
Energy Density ◽  
Time Dependence ◽  
Gravitational Waves ◽  
Hubble Parameter ◽  
Frequency Dependent ◽  
Cosmological Expansion ◽  
Relic Gravitational Waves ◽  
Matter Energy ◽  
Inflationary Models

The spectra of relic gravitational waves produced as a result of cosmological expansion of the inflationary models are derived in Brans–Dicke (BD) theory of gravity. The time dependence of the very early Hubble parameter and matter energy density are derived from frequency-dependent spectrum of relic gravitational waves. Also it is found that Brans–Dicke scalar field contributes to the energy density of relic gravitons.

Turning very long tensor perturbations into effective gravitational waves: An estimate of the gravitons’ back reaction

1997 ◽  
Vol 56 (10) ◽  
pp. 6351-6362 ◽  
Author(s):  
M. R. de Garcia Maia ◽  
J. C. Carvalho ◽  
J. S. Alcaniz
Keyword(s):  
Gravitational Waves ◽  
Back Reaction ◽  
Tensor Perturbations

scholarly journals EARLY UNIVERSE SOURCES FOR CMB NON-GAUSSIANITY

2002 ◽  
Vol 17 (29) ◽  
pp. 4273-4280
Author(s):  
ALEJANDRO GANGUI
Keyword(s):  
Power Spectrum ◽  
Cosmic Microwave Background ◽  
Early Universe ◽  
Microwave Background ◽  
Scale Invariant ◽  
Invariant Model ◽  
Primordial Power Spectrum ◽  
Initial States ◽  
Non Gaussian ◽  
Inflationary Models

In the framework of inflationary models with non-vacuum initial states for cosmological perturbations, we study non-Gaussian signatures on the cosmic microwave background (CMB) radiation produced by a broken-scale-invariant model which incorporates a feature at a privileged scale in the primordial power spectrum.

Inflation with non-minimally derivative coupling

2015 ◽  
Vol 30 (28n29) ◽  
pp. 1545004 ◽  
Author(s):  
Nan Yang ◽  
Qing Gao ◽  
Yungui Gong
Keyword(s):  
Gravitational Waves ◽  
Power Law ◽  
Second Order ◽  
Order Correction ◽  
Observational Constraint ◽  
Derivative Coupling ◽  
Primordial Gravitational Waves ◽  
Inflationary Models

We derive the second order correction to the scalar and tensor spectral tilts for the inflationary models with non-minimally derivative coupling. In the high friction limit, the quartic power law potential is consistent with the observational constraint at 95% CL because the amplitude of the primordial gravitational waves is smaller, and the inflaton excursion is sub-Planckian.

Sign in / Sign up

Export Citation Format

Share Document