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ARCHIVE
2003
Seminar Number
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Seminar Date
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Seminar Date
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Title and Abstract
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December,10
December,0
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A.G.Pol
A.G.Polnarev |
Electromagnetic
waves propagation in random field of gravitational waves
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No.130
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November,19
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V.M.Chechetkin
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Jets and
plasma instabilities
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No.129
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November,5
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S.D. Odintsov
(TSPU, Tomsk, RUSSIA and IEEC,Barcelona, SPAIN)
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Modified gravity as gravitational alternative to
dark energy and cosmic acceleration
The number of gravity theories are considered where lagrangian contains
the terms growing with the decrease of the scalar curvature. Simplest
example is 1/R gravity. Such models elliminate the need in the dark
energy, as correspondent gravitational terms are responsible for cosmic
acceleration. The string/M-theory origin of such effective gravities is
shown. The resolution of the appearing instabilities by the
introduction of higher derivative terms important for early time
inflation is outlined.
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No.128
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October, 1
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A.N.Petrov
(SAI MSU)
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The background spacetime method and conservation
laws in GR
General relativity is presented as an exact theory
of perturbations on arbitrary curved backgrounds. The conserved
currents (vector densities) is constructed as divergences of
superpotentials (antisymmetrical tensor densities). It is studied both
the cononical method beginning from Einstein's approach to the problem
of enegry in GR, and the symmetrical method based on costructing a
symmetrical (metric) energy-momentum tensor for perturbations. The
connection between these approaches is found. 1) Asymptotically flat
spacetimes
both at spatial and at null infinity; 2) cosmological perturbations on
FRW-backgrounds;
3) some methodological problems of black hole solutions are considered
for
applications of the theoretical results.
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No.127
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June, 25
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A.Linde
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Inflation, dark
energy,
and the future of the universe
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No.126
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June, 4
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S.Kopeikin (Univ. of Missouri-Columbia, USA)
and
Ed Fomalont (NRAO, USA)
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The measurement of relativistic
effect of light deviation
in Jupiter gravitational field: experimental results and theoretical
interpretation
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No.125
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May, 28
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1. D.Podolskiy (PhD work presentation)
2. G. B. Lesovik, A. V. Lebedev, V. Mounutcharyan, T. Martin
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Detection of gravitational waves by phase and
frequency modulation of the light from a distant star
We
propose a novel method for detecting gravitational waves (GW), where a
light signal emitted from a distant star interacts with a local (also
distant) GW source and travels towards the Earth, where it is detected.
While traveling in the field of the GW, the light acquires specific
phase
modulation (which we account in the eikonal approximation). This phase
modulation can be considered as a coherent spreading of the given
initial photons energy over a set of satellite lines, spaced at the
frequency of GW
(from quantum point of view it is multi-graviton absorbtions and
emittion processes). This coherent states of photons with the energy
distributed among the set of equidistant lines, can be analyzed and
identified on Earth either by passing the signal through a Fabry-Perot
filter or by monitoring the intensity-intensity correlations at
different
times. [The latter option reminds about the analogous effect known in
mesoscopic physics, with the substitution of electrons instead of
photons,
periodical electromagnetic field instead of gravitational wave and
multiple
photon processes by multiple graviton processes (so called photon
assisted
noise, or Lesovik-Levitov effect).] The described phase modulation in
light
is very similar in its form to that, which
occurs because of the Doppler effect due to a rotational motion of the
light source. The two effects can be distinguished only by the
astrophysical or observational astronomy means, e.g. the effect we
describe is nearly the same for all the distant light sources within
some apparent volume (spot) around the apparent
position of the GW source, while one hardly expects synchronized
rotation of several distant stars.
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No.124
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May,21
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D.V. Gal'tsov
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S-branes and accelerating universes
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No.123
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April,30
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A.V. Gurevich,
K.P. Zybin, A.S. Il'in
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Dark matter and gigant black holes
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No.122
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April,16
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D.D.Sokolov
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Topological inflation possibility
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No.121
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April,2
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1) Postnov K.A., Zakharov A.B.
2) Babichev E.O., Docuchaev V.I.
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1)NEWS
2)Chiral cosmic strings
The general properties of cosmic string with superconducting chiral
current are reviewed. The most interesting feature of superconducting
cosmic strings is the possibility of stationary configurations called
'vortons'. We describe in details the gravitational and electromagnetic
radiation from closed chiral strings. Some astrophysical applications
of chiral cosmic strings are considered: the string oscillations
damping
to vorton state, the specifics of gravitational lensing by vortons, the
existence of cutoff frequency in the gravitational radiation of chiral
string cusp.
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No.120
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March,19
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1)A.A.Starobinsky
(U. Alam, V.
Sahni, A.A. Starobinsky)
2)A.M.Cherepashchuk, K.A.Postnov
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1)Is
dark energy decaying? (astro-ph/0302302)
2)Stellar black hole mass function:
determination and possible implications
for fundamental gravity
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1)
We explore the fate of the universe
given the possibility that the density associated with `dark energy'
may decay slowly with time. We model decaying dark energy by a
homogeneous scalar field which couples minimally to gravity and whose
potential has{\em at least one} local maximum. Dark energy decays as
the scalar field rolls down its potential and this allows for several
interesting possibilities including: (i) the current acceleration
epoch can be a transient, (ii) a spatially flat universe ultimately
collapses
under the influence of a growing negative potential. (The second
possibility
is realized by the cosine potential.) We examine both possibilities by
comparing
our model universe with observations of high redshift type Ia
supernovae.
A maximum likelihood analysis reveals that such models are viable if
the
effective mass squared near the potential maximum is small ($m \sim
H_0$)
and if the initial field displacement is not very large $\phi/M_P \lleq
1$.
The time left until the universe collapses is always larger than $\sim
22$
Gyrs for $\om = 0.3$ and $H_0 \simeq 70$ km/sec/Mpc (at the 95.4%
confidence level).
2) We critically assess the errors in
determination of stellar mass black holes in close binaries and
construct the BH mass function available from current astronomical
observations. We show that there is a
statistically real gap between the currently known masses of neutron
stars and the lower BH masses (at around 3-4 M_\odot) and that the
observed BH mass function has approximately flat shape in the range
from 3 to 20 solar masses. Apart from astrophysical explanation to this
gap and BH mass distribution, we speculate on the possible origin of
such features as arising from fundamental properties of gravity.
Specifically, we consider BH in the 5D brane models (of RS2 type) and
argue that it is the Hawking evaporation of BH through
CFT-modes that shapes the observed BH mass function. In this instance,
in order to match the observed distribution the initial BH mass
function should have a power-law shape with index close to the Salpeter
(-2.35) or Miller-Scalo exponent (-2.5), which may have deep
consequences for stellar BH formation theory.
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No.119
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March,5
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M.V.Sazhin
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CSL1:chance projection effect or serendipitous
discovery of a gravitational lens induced by
a cosmic string
CSL1
(Capodimonte-Sternberg-Lens Candidate N1) is an extragalactic double
source detected in the OACDF (Osservatorio Astronomico di Capodimonte -
Deep Field) It can be interpreted either as the chance alignment of two
identical galaxies at z=0.46 or as the first case of gravitational
lensing by a cosmic string. Extensive modeling shows in fact that
cosmic strings are the only type of lens which (at least at low angular
resolution) can produce undistorted double images of a background
source. We propose an experimentum crucis to disentangle between these
two possible explanations. If the lensing by a cosmic string should be
confirmed, it would provide the first measurements of energy scale of
symmetry breaking and of the energy scale of Grand Unified Theory
(GUT).
=
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No.118
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February,26
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1.M.V.Sazhin, A.A.Starobinkiy;
2.V.N.Pervushin
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| 1.
CMBR anisotropy and polarization. WMAP |
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2.Astrophysics
in relative units and conformal unified theory
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Astrophysical data on the
Supernova luminosity-distance -- redshift relations,
recalculated in terms of relative measurement
standards, are utillized as a justification of conformal-invariant unified
theory, where all masses, including masses
of the Planck and Higgs, become the present-day values of
dynamic variable of evolution of the univers in a regime
of the dominances of a free scalar field. Planck epochcosmological
creation from physical vacuum of W-, Z- of bosons. There are
initial data of the cosmic evolution, which describe in
framework of Standard Model.
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No.117
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February,12
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1.A.Starobinskiy
2.O.Khovanskaya
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1. NEWS
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2.
Strong gravitational fields:
opportunities of observations
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I represent the PhD thesis
dedicated to relations between superstring theories and primordial
black holes in frames of four
dimensional string gravity with two-loop correction and dilaton scalar
field.
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No.116
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January,29
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1.E.Koptelova
2.S.Alexeyev
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1. NEWS
2. Black hole solutions on branes
A
short review of the current situation
on black hole solutions in the frames
of models with non compact extra dimensions.
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No.115
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January,15
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M.V.Pomazanov
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The problem of singularities of higher
order curvature
corrections in four dimensional string
gravity
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The
influence of higher order - stringly inspired - curvature corrections
to the classical General Relativity spherically symmetric solution is
studied. These curvature corrections provide a singular contribution to
the field equations because they generate higher derivatives of metric
functions multiplied by a small parameter (the string coupling
constant). Analytically and numerically, it is shown that in both
Bosonic and Heterotic string gravity, the Schwarzschild solution is not
recovered when the string coupling constant vanishes. It seems that only Superstring II low
energy model does not induce any singular contribution in spherically
symmetric static space times.
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