scholarly journals Towards observational constraints on a negative (1+z)4 type contribution in the Friedmann equation

2006 ◽  
Vol 642 (1-2) ◽  
pp. 13-17 ◽  
Author(s):  
Włodzimierz Godłowski ◽  
Marek Szydłowski
Keyword(s):  
Friedmann Equation ◽  
Observational Constraints ◽  
Type Contribution

scholarly journals A note on supergravity inflation in braneworld

2021 ◽  
Vol 36 (07) ◽  
pp. 2150056
Author(s):  
Mudassar Sabir ◽  
Waqas Ahmed ◽  
Yungui Gong ◽  
Shan Hu ◽  
Tianjun Li ◽  
...  
Keyword(s):  
Energy Density ◽  
Friedmann Equation ◽  
High Energy ◽  
Index Formula ◽  
Observational Constraints ◽  
Braneworld Cosmology ◽  
Numerical Predictions ◽  
Scalar Spectral Index ◽  
High Energy Regime ◽  
Text Correction

We discuss supergravity inflation in braneworld cosmology for the class of potentials [Formula: see text] with [Formula: see text]. These minimal SUGRA models evade the [Formula: see text] problem due to a broken shift symmetry and can easily accommodate the observational constraints. In the high energy regime [Formula: see text], the numerical predictions and approximate analytic formulas are given for the scalar spectral index [Formula: see text] and tensor-to-scalar ratio [Formula: see text]. The models with smaller [Formula: see text] are preferred while the models with larger [Formula: see text] are out of the [Formula: see text] region. Remarkably, the [Formula: see text] correction to the energy density in Friedmann equation results in sub-Planckian inflaton excursions [Formula: see text].

scholarly journals Observational Constraints on Cosmology from the Modified Friedmann Equation

2004 ◽  
Vol 603 (2) ◽  
pp. 365-370 ◽  
Author(s):  
Zong‐Hong Zhu ◽  
Masa‐Katsu Fujimoto ◽  
Xiang‐Tao He
Keyword(s):  
Friedmann Equation ◽  
Observational Constraints

Observational Constraints on Models of the Solar Background Spectrum

1999 ◽  
Vol 516 (2) ◽  
pp. 939-945 ◽  
Author(s):  
Th. Straus ◽  
G. Severino ◽  
F.‐L. Deubner ◽  
B. Fleck ◽  
S. M. Jefferies ◽  
...  
Keyword(s):  
Observational Constraints ◽  
Background Spectrum

A Realistic Grid of Models for the Gravitationally Lensed Einstein Cross (Q2237+0305) and Its Relation to Observational Constraints

1998 ◽  
Vol 495 (2) ◽  
pp. 609-616 ◽  
Author(s):  
Kyu‐Hyun Chae ◽  
David A. Turnshek ◽  
Valery K. Khersonsky
Keyword(s):  
Observational Constraints

scholarly journals Cosmic Analogues of Classic Variational Problems

Universe ◽  
2020 ◽  
Vol 6 (6) ◽  
pp. 71 ◽  
Author(s):  
Valerio Faraoni
Keyword(s):  
Relativistic Particle ◽  
Friedmann Equation ◽  
Variational Calculus ◽  
Variational Problems ◽  
Particle Mechanics ◽  
One Dimensional ◽  
Spatially Homogeneous

Several classic one-dimensional problems of variational calculus originating in non-relativistic particle mechanics have solutions that are analogues of spatially homogeneous and isotropic universes. They are ruled by an equation which is formally a Friedmann equation for a suitable cosmic fluid. These problems are revisited and their cosmic analogues are pointed out. Some correspond to the main solutions of cosmology, while others are analogous to exotic cosmologies with phantom fluids and finite future singularities.

scholarly journals CHAOTIC INFLATION ON THE RANDALL–SUNDRUM TWO-BRANE MODEL

2010 ◽  
Vol 25 (31) ◽  
pp. 2697-2713
Author(s):  
KOUROSH NOZARI ◽  
SIAMAK AKHSHABI
Keyword(s):  
Scalar Field ◽  
Field Potential ◽  
Friedmann Equation ◽  
Warp Factor ◽  
Model Parameters ◽  
Stabilization Mechanism ◽  
Brane Model ◽  
Inflation Model ◽  
Bulk Scalar Field ◽  
Chaotic Inflation

We construct an inflation model on the Randall–Sundrum I (RSI) brane where a bulk scalar field stabilizes the inter-brane separation. We study impact of the bulk scalar field on the inflationary dynamics on the brane. We proceed in two different approaches: in the first approach, the stabilizing field potential is directly appeared in the Friedmann equation and the resulting scenario is effectively a two-field inflation. In the second approach, the stabilization mechanism is considered in the context of a warp factor so that there is just one field present that plays the roles of both inflaton and stabilizer. We study constraints imposed on the model parameters from recent observations.

scholarly journals Magnetospheric Structure of Rotation-Powered Neutron Stars

1992 ◽  
Vol 128 ◽  
pp. 56-77 ◽  
Author(s):  
Jonathan Arons
Keyword(s):  
Radio Emission ◽  
Gamma Radiation ◽  
Heavy Ions ◽  
Theoretical Work ◽  
Future Research ◽  
Observational Constraints ◽  
Polar Caps ◽  
Recent Theoretical Work ◽  
Density Flow ◽  
Promising Avenue

AbstractI survey recent theoretical work on the structure of the magnetospheres of rotation-powered pulsars, within the observational constraints set by their observed spindown, their ability to power synchrotron nebulae and their ability to produce beamed collective radio emission, while putting only a small fraction of their energy into incoherent X- and gamma radiation. I find no single theory has yet given a consistent description of the magnetosphere, but I conclude that models based on a dense outflow of pairs from the polar caps, permeated by a lower density flow of heavy ions, are the most promising avenue for future research.

scholarly journals Can the Local Bubble explain the radio background?

2021 ◽  
Vol 502 (2) ◽  
pp. 2807-2814
Author(s):  
Martin G H Krause ◽  
Martin J Hardcastle
Keyword(s):  
Magnetic Field ◽  
Energy Density ◽  
Radio Emission ◽  
Magnetic Energy ◽  
Cosmic Ray ◽  
Observational Constraints ◽  
Local Bubble ◽  
Magnetic Energy Density ◽  
Magnetic Field Model ◽  
Radio Background

ABSTRACT The ARCADE 2 balloon bolometer along with a number of other instruments have detected what appears to be a radio synchrotron background at frequencies below about 3 GHz. Neither extragalactic radio sources nor diffuse Galactic emission can currently account for this finding. We use the locally measured cosmic ray electron population, demodulated for effects of the Solar wind, and other observational constraints combined with a turbulent magnetic field model to predict the radio synchrotron emission for the Local Bubble. We find that the spectral index of the modelled radio emission is roughly consistent with the radio background. Our model can approximately reproduce the observed antenna temperatures for a mean magnetic field strength B between 3 and 5 nT. We argue that this would not violate observational constraints from pulsar measurements. However, the curvature in the predicted spectrum would mean that other, so far unknown sources would have to contribute below 100 MHz. Also, the magnetic energy density would then dominate over thermal and cosmic ray electron energy density, likely causing an inverse magnetic cascade with large variations of the radio emission in different sky directions as well as high polarization. We argue that this disagrees with several observations and thus that the magnetic field is probably much lower, quite possibly limited by equipartition with the energy density in relativistic or thermal particles (B = 0.2−0.6 nT). In the latter case, we predict a contribution of the Local Bubble to the unexplained radio background at most at the per cent level.

Observational constraints on low cloud feedback reduce uncertainty of climate sensitivity

2021 ◽  
Author(s):  
Timothy A. Myers ◽  
Ryan C. Scott ◽  
Mark D. Zelinka ◽  
Stephen A. Klein ◽  
Joel R. Norris ◽  
...  
Keyword(s):  
Climate Sensitivity ◽  
Cloud Feedback ◽  
Observational Constraints ◽  
Low Cloud
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