KEK Cosmophysics Workshop DE2008
Program 

Date 
10:00 
11:00 
12:00 
1:00 
2:00 
3:00 
4:00 
5:00 
6:00 
7:00 
8:00 

Dec. 8 (Mon) 

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R. Ali Vanderveld 
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(CB) 
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Welcome Dinner 

Dec. 9 (Tue) 
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Lunch 
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(CB) 
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Dec.10 (Wed) 
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Lunch 
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(CB) 
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WS Dinner (Urban H.) 

Dec.11 (Thu) 
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Lunch 
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(CB) 
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Dec.12 (Fri) 
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2008/12/8(Mon) 

Ishibashi, A. 
A
brief overview of the ideas and issues of the effects of inhomogeneities on
cosmic expansion 
Vanderveld, R.A. 
Voids
and Supernova Cosmology 
Abstract:
I will review the ways in which voids in the large scale matter distribution
can impede supernova cosmology, with a focus on whether or not they can mimic
accelerated expansion. This
discussion will first focus on the scenario in which the observer lives
within a void, and then it will turn to what happens when there are voids
along the line of sight connecting observer and source. 

Nakao, K.I. 
Solving
the inverse problem with inhomogeneous universes 
We
construct the Lema\^itreTolmanBondi (LTB) dust universe whose
distanceredshift relation is equivalent to that in the concordance $\Lambda$
cold dark matter ($\Lambda$CDM) cosmological model. In our model, the density
distribution and velocity field are not homogeneous, whereas the bigbang
time is uniform, which implies that the universe is homogeneous at its
beginning. We also study the effects of local clumpiness in the density
distribution as well as the effects of largescale inhomogeneities on the
distanceredshift relation, and show that these effects may reduce the
amplitude of largescale inhomogeneities necessary for having a
distanceredshift relation that is the same as that of the concordance
$\Lambda$CDM universe. We also study the temporal variation of the
cosmological redshift and show that, by the observation of this quantity, we
can distinguish our LTB universe model from the concordance $\Lambda$CDM
model, even if their redshiftdistance relations are equivalent to each
other. 

2008/12/9(Tue) 

Kasai, M. 
Dark
Energy? Backreaction? Inhomogeneous viewpoint! 
I
briefly review the backreaction of nonlinear inhomogeneities to the 

Notari, A. 
Can
an Inhomogeneous Universe mimic Dark Energy? 
In
this talk I will review recent attempts to explain cosmological 

Starobinsky, A.A. 
Strengthening
arguments for quasihomogeneous accelerated expansion of the Universe 
Recent
numerous observational data obtained from such independent sources as the
temperature angular anisotropy and polarization of the cosmic microwave
background radiation, largescale gravitational clustering of galaxies and
their clusters and observations of supernovae explosions at high redshifts
prove convincingly that the Universe expands with acceleration at the present
time while it was decelerating in the past for redshifts larger than about
0.7. If interpreted in terms of the Einstein general relativity, this means
that the about 70% of the total energy density of matter in the present Universe
is due to a new (effective) kind of matter in the Universe ("dark
energy") which is nonbaryonic, has negative pressure which modulus is
very close to its energy density, and remains unclustered at all scales where
clustering of baryons and dustlike cold dark matter is seen. 

2008/12/10(Wed) 

Inoue, K.T. 
Local
Supervoids and the Origin of the WMAP Cold Spot 
We
discuss the origin of the WMAP Cold Spot. We have found that a quasilinear
supervoid with radius ~ 200h^{1}Mpc at redshift z<1 toward the Spot could
generate such a cold spot via the linear integrated SachsWolfe (ISW) effect.
However, in the standard LCDM scenarios, the chance of having such a
supervoid is extremely rare. Due to a correlation between the firstorder and
the secondorder ISW effect, the CMB temperature would be negatively biased
if such superstructures are abundant in the local universes. 

Wiltshire, D. 
Cosmological
equivalence principle and dark energy 
(GCJS) 
The
problem of the synchronization of clocks and normalization of gravitational
energy in general relativity does not have a unique or obvious solution in
the absence of exact symmetries of the background. I return to first
principles and extend the strong equivalence principle in application to
averaged dynamical fields in cosmology, to include the role of the evolving
average background density in the calibration of inertial frames. This leads
to a "radically conservative" solution to the problem of dark
energy in cosmology, using only general relativity and matter obeying the strong
energy condition. The proposal yields a model universe which appears to be
quantitatively viable, in terms of its fit to supernovae luminosity
distances, the angular scale of the sound horizon in the cosmic microwave
background anisotropy spectrum, and the baryon acoustic oscillation scale. I
will briefly overview the observational status of the proposal, as well as
discussing the foundational issues. 
Futamase, T. 
Recent
developements of weak lensing 
(GCJS) 

2008/12/11(Thu) 

Wiltshire, D. 
Dark
energy without dark energy: Average observational quantities 
I
have proposed that the phenomenon of dark energy is a misidentification of
gravitational energy gradients in a presently inhomogeneous universe
dominated by voids, typically of diameter 30/h Mpc. In this talk I will
further discuss the physical basis of the proposal in relation to the debate
about averaging and backreaction in inhomogeneous cosmology. I will provide
further details and outline future observational tests which will distinguish
the proposal from standard dark energy models in a homogeneous universe. 

2008/12/12(Fri) 

Asada, H. 
Toward
understanding the light propagation in the clumpy universe Perturbation theory
of N point mass gravitational lens 
Roman, A.E. 
Inhomogeneities
as alternatives to dark energy 
Tomita, K. 
On
astrophysical explanations due to inhomogeneities for the observational
cosmological acceleration 