5,474 research outputs found
Testing Gravity Against Early Time Integrated Sachs-Wolfe Effect
A generic prediction of general relativity is that the cosmological linear
density growth factor is scale independent. But in general, modified
gravities do not preserve this signature. A scale dependent can cause time
variation in gravitational potential at high redshifts and provides a new
cosmological test of gravity, through early time integrated Sachs-Wolfe (ISW)
effect-large scale structure (LSS) cross correlation. We demonstrate the power
of this test for a class of gravity, with the form . Such gravity, even with degenerate
expansion history to CDM, can produce detectable ISW effect at z\ga
3 and l\ga 20. Null-detection of such effect would constrain to
be at confidence level. On the other hand, robust
detection of ISW-LSS cross correlation at high will severely challenge
general relativity.Comment: 5 pages, 2 figures. Accepted to PRD. v2: Revised to address to more
general audience. v3: added discussion
Dark Energy Accretion onto a Black Hole in an Expanding Universe
By using the solution describing a black hole embedded in the FLRW universe,
we obtain the evolving equation of the black hole mass expressed in terms of
the cosmological parameters. The evolving equation indicates that in the
phantom dark energy universe the black hole mass becomes zero before the Big
Rip is reached.Comment: 7 pages, no figures, errors is correcte
Vacuum Energy: If Not Now, Then When?
We review the cosmological evidence for a low matter density universe and a
cosmological constant or dynamical vacuum energy and address the cosmolog$
coincidence problem: why is the matter density about one-half the vacuum energy
{\em now}. This is reasonble, following the anthropic argument of Efstathiou
and of Martel, Schapiro & Weinberg.Comment: 4 pages (latex
Accelerated expansion in modified gravity with a Yukawa-like term
We discuss the Palatini formulation of modified gravity including a
Yukawa-like term. It is shown that in this formulation, the Yukawa term offers
an explanation for the current exponential accelerated expansion of the
universe and reduces to the standard Friedmann cosmology in the appropriate
limit. We then discuss the scalar-tensor formulation of the model as a metric
theory and show that the Yukawa term predicts a power-law acceleration at
late-times. The Newtonian limit of the theory is also discussed in context of
the Palatini formalism.Comment: 9 pages, 2 figures, to appear in IJMP
Measuring the properties of extragalactic dust and implications for the Hubble diagram
Scattering and absorption of light by a homogeneous distribution of
intergalactic large dust grains has been proposed as an alternative,
non-cosmological explanation for the faintness of Type Ia supernovae at z\s im
0.5. We investigate the differential extinction for high-redshift sources
caused by extragalactic dust along the line of sight.
Future observations of Type Ia supernovae up to , e.g. by the
proposed SNAP satellite, will allow the measurement of the properties of dust
over cosmological distances. We show that 1% {\em relative} spectrophotometric
accuracy (or broadband photometry) in the wavelength interval 0.7--1.5 m
is required to measure the extinction caused by ``grey'' dust down to magnitudes.
We also argue that the presence of grey dust is not necessarily inconsistent
with the recent measurement of the brightness of a supernova at (SN
1997ff), in the absence of accurate spectrophotometric information of the
supernova.Comment: Accepted by A&
Eternally inflating cosmologies from intersecting spacelike branes
Intersecting spacelike braneworld cosmologies are investigated. The time axis
is set on the scale parameter of extra space, which may include more than one
timelike metric. Obtained are eternally inflating (i.e. undergoing late-time
inflation) Robertson-Walker spacetime and extra space with a constant scale
factor. In the case of multibrane solutions, some dimensions are static or
shrink. The fact that the largest supersymmetry algebra contains 32
supercharges in 4 dimensions imposes a restriction on the geometry of extra
space.Comment: 19 page
Model-Independent Distance Measurements from Gamma-Ray Bursts and Constraints on Dark Energy
Gamma-Ray Bursts (GRB) are the most energetic events in the Universe, and
provide a complementary probe of dark energy by allowing the measurement of
cosmic expansion history that extends to redshifts greater than 6. Unlike Type
Ia supernovae (SNe Ia), GRBs must be calibrated for each cosmological model
considered, because of the lack of a nearby sample of GRBs for
model-independent calibration. For a flat Universe with a cosmological
constant, we find Omega_m=0.25^{+0.12}_{-0.11} from 69 GRBs alone. We show that
the current GRB data can be summarized by a set of model-independent distance
measurements, with negligible loss of information. We constrain a dark energy
equation of state linear in the cosmic scale factor using these distance
measurements from GRBs, together with the "Union" compilation of SNe Ia, WMAP
five year observations, and the SDSS baryon acoustic oscillation scale
measurement. We find that a cosmological constant is consistent with current
data at 68% confidence level for a flat Universe. Our results provide a simple
and robust method to incorporate GRB data in a joint analysis of cosmological
data to constrain dark energy.Comment: 8 pages, 5 color figures. Version expanded and revised for
clarification, and typo in Eqs.(3)(4)(12) corrected. PRD, in pres
Sport, Representation and Culture in the Modern World, 1920-2020
Cultural historians study the change of human civilization over time. They focus on people’s beliefs, rituals, ideas, identity, social norms, institutions, and materials, with particular attention to the meanings of that culture’s elements (Hutton 1981). Cultural historians before World War II focused on high culture, but thereafter, because of the influence of cultural anthropology, they began to study popular culture, that include every day experiences and artifacts that express mass values and attitudes. Since the late 1960s, scholars have studied sport’s interaction with high and low culture, and also sport as an independent element of culture with s symbolic acts, representation, and struggle over meaning of sport’s myths and realities
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