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Arxiv (Free subscription) | 32 minutes ago
We study the generation of primordial perturbations in a (single-field) slow-roll inflationary universe. In momentum space, these (Gaussian) perturbations are characterized by a zero mean and a non-zero variance $\Delta^2(k, t)$. However, in position space the variance diverges in the ultraviolet. The requirement of a finite variance in position space forces one to regularize $\Delta^2(k, t)$. This...
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Arxiv (Free subscription) | 32 minutes ago
CMB measurements reveal an unnaturally smooth early universe. We propose a mechanism to make this smoothness natural by weakening the strength of gravity at early times, and therefore altering which initial conditions have low entropy.
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Arxiv (Free subscription) | 32 minutes ago
The problem of cosmological particle creation for a spatially flat, homogeneous and isotropic Universes is discussed in the context of f(R) theories of gravity. Different from cosmological models based on general relativity theory, it is found that a conformal invariant metric does not forbid the creation of massless particles during the early stages (radiation era) of the Universe.
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Arxiv (Free subscription) | 32 minutes ago
The prediction of the spin of the black hole resulting from the merger of a generic black-hole binary system is of great importance to study the cosmological evolution of supermassive black holes. Several attempts have been recently made to model the spin via simple expressions exploiting the results of numerical-relativity simulations. Here I compare the results of all the simulations appeared so...
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Arxiv (Free subscription) | 32 minutes ago
Gowdy waves, one of the standard 'apples with apples' tests, is proposed as a test-bed for constraint-preserving boundary conditions in the non-linear regime. As an illustration, energy-constraint preservation is separately tested in the Z4 framework. Both algebraic conditions, derived from energy estimates, and derivative conditions, deduced from the constraint-propagation system, are considered....
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Arxiv (Free subscription) | 32 minutes ago
We investigate static spherically symmetric vacuum solutions in the IR limit of projectable nonrelativistic quantum gravity, including the renormalisable quantum gravity recently proposed by Ho\v{r}ava. It is found that the projectability condition plays an important role. Without the cosmological constant, the spacetime is uniquely given by the Schwarzschild solution. With the cosmological constant,...
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Arxiv (Free subscription) | 32 minutes ago
We study relativistic stars in the context of scalar tensor theories of gravity that try to account for the observed cosmic acceleration and satisfy the local gravity constraints via the chameleon mechanism. More specifically, we consider two types of models: scalar tensor theories with an inverse power law potential and f(R) theories. Using a relaxation algorithm, we construct numerically static...
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Arxiv (Free subscription) | 32 minutes ago
We study the causal structure of dynamical charged black holes, with a sufficient number of massless fields, using numerical simulations. Neglecting Hawking radiation, the inner horizon is a null Cauchy horizon and a curvature singularity due to mass inflation. When we include Hawking radiation, the inner horizon becomes space-like and is separated from the Cauchy horizon, which is parallel to the...
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Red Orbit (Free subscription) | yesterday
Image Caption: This is a composite of false color images of the galaxies found at the early epoch around 800 million years after the Big Bang. The upper left panel presents the galaxy confirmed in the 787 million year old universe. These galaxies are in the Subaru Deep Field. Credit: These images are created by M. Ouchi et al.
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Astronomy Cmarchesin (Free subscription) | 11/06/2009
False color image of the Z7 galaxy This is a composite of false color images of the galaxies found at the early epoch around 800 million years after the Big Bang. The upper left panel presents the galaxy confirmed in the 787 million year old universe. These galaxies are in the Subaru Deep Field. (These images are created by M. Ouchi et al., which are the reproduction of Figure 3 in the Astrophysical...
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Universe Today (Free subscription) | 11/06/2009
Astronomers looking to pinpoint when the reionozation of the Universe took place have found some of the earliest galaxies about 800 million years after the Big Bang. 22 early galaxies were found using a method that looks for far-away redshifting sources that disappear or "drop-out" at a specific wavelength. The age of one [...]
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Physorg (Free subscription) | 11/06/2009
Astronomers, conducting the broadest survey to date of galaxies from about 800 million years after the Big Bang, have found 22 early galaxies and confirmed the age of one by its characteristic hydrogen signature at 787 million years post Big Bang. The finding is the first age-confirmation of a so-called dropout galaxy at that distant time and pinpoints when an era called the reionization epoch likely...
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Arxiv (Free subscription) | 11/06/2009
The magnetogenesis scenarios triggered by the early variation of the gauge coupling are critically analyzed. In the absence of sources, it is shown that the electric and magnetic power spectra can be explicitly computed by means of electric-magnetic duality transformations. The remnants of a pre-inflationary expansion and the reheating process break explicitly electric-magnetic duality by inducing...
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Arxiv (Free subscription) | 11/06/2009
A solenoid oscillating in vacuum will pair produce charged particles due to the Aharonov-Bohm (AB) interaction. We calculate the radiation pattern and power emitted for charged scalar particles. We extend the solenoid analysis to cosmic strings, and find enhanced radiation from cusps and kinks on loops. We argue by analogy with the electromagnetic AB interaction that cosmic strings should emit photons...
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Arxiv (Free subscription) | 11/06/2009
We present long term evolutions of a single black hole of mass $M$ with the BSSN system using pseudo-spectral methods. For our simulations we use the SGRID code where the BSSN system is implemented in its standard second order in space form. Previously we found that that such simulations are quite unstable. The main goal of this paper is to present two improvements which now allow us to evolve for...
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aronaldox7 | 01/08/2009
Visit site for watching video of episode The Dumpling Paradox
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en - (not a member) - 09/29/2009
There’s only one legitimate place I’ve found to watch it, the rest seem like scams :-/ You can watch it over here though: http://www.vostuu.com/bigbangtheory.html
They...
en - (not a member) - 05/15/2009
thanks
en - (not a member) - 02/25/2009
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stephaxml | 12/20/2008
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csomboza | 12/11/2008
On The Big Bang Theory Season 2 Episode 11 , you will notice that Christmas is stressing out Leonard because his handsome colleague is now dating Penny and Leonard together with his friends are bothered by Sheldon’s obsession of giving presents for Christmas.
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