120 research outputs found

### FRW Universe Models in Conformally Flat Spacetime Coordinates. I: General Formalism

The 3-space of a universe model is defined at a certain simultaneity. Hence
space depends on which time is used. We find a general formula generating all
known and also some new transformations to conformally flat spacetime
coordinates. A general formula for the recession velocity is deduced.Comment: 12 page

### Entropy creation inside black holes points to observer complementarity

Heating processes inside large black holes can produce tremendous amounts of
entropy. Locality requires that this entropy adds on space-like surfaces, but
the resulting entropy (10^10 times the Bekenstein-Hawking entropy in an example
presented in the companion paper) exceeds the maximum entropy that can be
accommodated by the black hole's degrees of freedom. Observer complementarity,
which proposes a proliferation of non-local identifications inside the black
hole, allows the entropy to be accommodated as long as individual observers
inside the black hole see less than the Bekenstein-Hawking entropy. In the
specific model considered with huge entropy production, we show that individual
observers do see less than the Bekenstein-Hawking entropy, offering strong
support for observer complementarity.Comment: 13 pages. This is a companion paper to arXiv:0801.4415; Added
reference

### Large-Scale Structure at z~2.5

We have made a statistically complete, unbiased survey of C IV systems toward
a region of high QSO density near the South Galactic Pole using 25 lines of
sight spanning $1.5<z<2.8$. Such a survey makes an excellent probe of
large-scale structure at early epochs. We find evidence for structure on the
$15-35h^{-1}$ proper Mpc scale ($H_0 \equiv 100$ km $s^{-1}$ Mpc${-1}$) as
determined by the two point C IV - C IV absorber correlation function, and
reject the null hypothesis that C IV systems are distributed randomly on such
scales at the $\sim 3.5\sigma$ level. The structure likely reflects the
distance between two groups of absorbers subtending $\sim~ 13 \times 5 \times
21h^{-3}$ and $\sim 7 \times 1 \times 15h^{-3}$ Mpc$^3$ at $z\sim 2.3$ and $z
\sim 2.5$ respectively. There is also a marginal trend for the association of
high rest equivalent width C IV absorbers and QSOs at similar redshifts but
along different lines of sight. The total number of C IV systems detected is
consistent with that which would be expected based on a survey using many
widely separated lines of sight. Using the same data, we also find 11 Mg II
absorbers in a complete survey toward 24 lines of sight; there is no evidence
for Mg II - Mg II or Mg II - QSO clustering, though the sample size is likely
still small to detect such structure if it exists.Comment: 56 pages including 32 of figures, in gzip-ed uuencoded postscript
format, 1 long table not included, aastex4 package. Accepted for publication
in ApJ Supplement

### Growth factor in f(T) gravity

We derive the evolution equation of growth factor for the matter over-dense
perturbation in $f(T)$ gravity. For instance, we investigate its behavior in
power law model at small redshift and compare it to the prediction of
$\Lambda$CDM and dark energy with the same equation of state in the framework
of Einstein general relativity. We find that the perturbation in $f(T)$ gravity
grows slower than that in Einstein general relativity if \p f/\p T>0 due to
the effectively weakened gravity.Comment: 15 pages,1 figure; v2,typos corrected; v3, discussions added,
accepted by JCA

### A river model of space

Within the theory of general relativity gravitational phenomena are usually
attributed to the curvature of four-dimensional spacetime. In this context we
are often confronted with the question of how the concept of ordinary physical
three-dimensional space fits into this picture. In this work we present a
simple and intuitive model of space for both the Schwarzschild spacetime and
the de Sitter spacetime in which physical space is defined as a specified set
of freely moving reference particles. Using a combination of orthonormal basis
fields and the usual formalism in a coordinate basis we calculate the physical
velocity field of these reference particles. Thus we obtain a vivid description
of space in which space behaves like a river flowing radially toward the
singularity in the Schwarzschild spacetime and radially toward infinity in the
de Sitter spacetime. We also consider the effect of the river of space upon
light rays and material particles and show that the river model of space
provides an intuitive explanation for the behavior of light and particles at
and beyond the event horizons associated with these spacetimes.Comment: 22 pages, 5 figure

### Consistency test of general relativity from large scale structure of the Universe

We construct a consistency test of General Relativity (GR) on cosmological
scales. This test enables us to distinguish between the two alternatives to
explain the late-time accelerated expansion of the universe, that is, dark
energy models based on GR and modified gravity models without dark energy. We
derive the consistency relation in GR which is written only in terms of
observables - the Hubble parameter, the density perturbations, the peculiar
velocities and the lensing potential. The breakdown of this consistency
relation implies that the Newton constant which governs large-scale structure
is different from that in the background cosmology, which is a typical feature
in modified gravity models. We propose a method to perform this test by
reconstructing the weak lensing spectrum from measured density perturbations
and peculiar velocities. This reconstruction relies on Poisson's equation in GR
to convert the density perturbations to the lensing potential. Hence any
inconsistency between the reconstructed lensing spectrum and the measured
lensing spectrum indicates the failure of GR on cosmological scales. The
difficulties in performing this test using actual observations are discussed.Comment: 7 pages, 1 figur

### Scaling in Numerical Simulations of Domain Walls

We study the evolution of domain wall networks appearing after phase
transitions in the early Universe. They exhibit interesting dynamical scaling
behaviour which is not yet well understood, and are also simple models for the
more phenomenologically acceptable string networks. We have run numerical
simulations in two- and three-dimensional lattices of sizes up to 4096^3. The
theoretically predicted scaling solution for the wall area density A ~ 1/t is
supported by the simulation results, while no evidence of a logarithmic
correction reported in previous studies could be found. The energy loss
mechanism appears to be direct radiation, rather than the formation and
collapse of closed loops or spheres. We discuss the implications for the
evolution of string networks.Comment: 7pp RevTeX, 9 eps files (including six 220kB ones

### Next-to-leading resummation of cosmological perturbations via the Lagrangian picture: 2-loop correction in real and redshift spaces

We present an improved prediction of the nonlinear perturbation theory (PT)
via the Lagrangian picture, which was originally proposed by Matsubara (2008).
Based on the relations between the power spectrum in standard PT and that in
Lagrangian PT, we derive analytic expressions for the power spectrum in
Lagrangian PT up to 2-loop order in both real and redshift spaces. Comparing
the improved prediction of Lagrangian PT with $N$-body simulations in real
space, we find that the 2-loop corrections can extend the valid range of wave
numbers where we can predict the power spectrum within 1% accuracy by a factor
of 1.0 ($z=0.5$), 1.3 (1), 1.6 (2) and 1.8 (3) vied with 1-loop Lagrangian PT
results. On the other hand, in all redshift ranges, the higher-order
corrections are shown to be less significant on the two-point correlation
functions around the baryon acoustic peak, because the 1-loop Lagrangian PT is
already accurate enough to explain the nonlinearity on those scales in $N$-body
simulations.Comment: 18pages, 4 figure

### Is cosmology consistent?

We perform a detailed analysis of the latest CMB measurements (including
BOOMERaNG, DASI, Maxima and CBI), both alone and jointly with other
cosmological data sets involving, e.g., galaxy clustering and the Lyman Alpha
Forest. We first address the question of whether the CMB data are internally
consistent once calibration and beam uncertainties are taken into account,
performing a series of statistical tests. With a few minor caveats, our answer
is yes, and we compress all data into a single set of 24 bandpowers with
associated covariance matrix and window functions. We then compute joint
constraints on the 11 parameters of the ``standard'' adiabatic inflationary
cosmological model. Out best fit model passes a series of physical consistency
checks and agrees with essentially all currently available cosmological data.
In addition to sharp constraints on the cosmic matter budget in good agreement
with those of the BOOMERaNG, DASI and Maxima teams, we obtain a heaviest
neutrino mass range 0.04-4.2 eV and the sharpest constraints to date on gravity
waves which (together with preference for a slight red-tilt) favors
``small-field'' inflation models.Comment: Replaced to match accepted PRD version. 14 pages, 12 figs. Tiny
changes due to smaller DASI & Maxima calibration errors. Expanded neutrino
and tensor discussion, added refs, typos fixed. Combined CMB data, window and
covariance matrix at http://www.hep.upenn.edu/~max/consistent.html or from
[email protected]

### Planck-scale quintessence and the physics of structure formation

In a recent paper we considered the possibility of a scalar field providing
an explanation for the cosmic acceleration. Our model had the interesting
properties of attractor-like behavior and having its parameters of O(1) in
Planck units. Here we discuss the effect of the field on large scale structure
and CMB anisotropies. We show how some versions of our model inspired by
"brane" physics have novel features due to the fact that the scalar field has a
significant role over a wider range of redshifts than for typical "dark energy"
models. One of these features is the additional suppression of the formation of
large scale structure, as compared with cosmological constant models. In light
of the new pressures being placed on cosmological parameters (in particular
H_0) by CMB data, this added suppression allows our "brane" models to give
excellent fits to both CMB and large scale structure data.Comment: 18 pages, 12 figures, submitted to PR

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