669 research outputs found
A view on the problems of Quantum Gravity
The existing approaches to quantization of gravity aim at giving quantum
description of 3-geometry following to the ideas of the Wheeler -- DeWitt
geometrodynamics. In this description the role of gauge gravitational degrees
of freedom is missed. A probable alternative is to consider gravitational
dynamics in extended phase space, taking into account the distinctions between
General Relativity and other field theories. The formulation in extended phase
space leads to some consequences at classical and quantum levels. At the
classical level, it ensures that Hamiltonian dynamics is fully equivalent to
Lagrangian dynamics, and the algebra of Poisson brackets is invariant under
reparametrizations in a wide enough class including reparametrizations of gauge
variables, meantime in the canonical Dirac approach the constraints' algebra is
not invariant that creates problems with quantization. At the quantum level,
the approach come to the description in which the observer can see various but
complementary quantum gravitational phenomena in different reference frames
that answers the spirit of General Relativity and Quantum Theory. Though until
now the approach was applied to General Relativity in its original
formulations, its implementation in different trends, including Quantum Loop
Gravity or some other representations of gravitational variables, would also be
of interest.Comment: 6 pages, talk presented at the International Conference on Quantum
Gravity "Loops 11", Madrid, May 201
The generality of inflation in some closed FRW models with a scalar field
The generality of inflation in closed FRW Universe is studied for the models
with a scalar field on a brane and with a complex scalar field. The results
obtained are compared with the previously known results for the model with a
scalar field and a perfect fluid. The influence of the measure chosen in the
initial condition space on the ratio of inflationary solution is described.Comment: 15 pages with 5 eps figures; small corrections in text; final version
to appear in Int. J. Mod. Phys.
Tien-Shan effect and charmed particles
It is shown that the Tien-Shan effect can be explained as a consequence of charmed particle production with a sufficiently high production cross-section (about 5 mb/nucleon at 100 TeV)
The exact cosmological solution to the dynamical equations for the Bianchi IX model
Quantum geometrodynamics in extended phase space describes phenomenologically
the integrated system ``a physical object + observation means (a gravitational
vacuum condensate)''. The central place in this version of QGD belongs to the
Schrodinger equation for a wave function of the Universe. An exact solution to
the ``conditionally-classical'' set of equations in extended phase space for
the Bianchi-IX model and the appropriate solution to the Schrodinger equation
are considered. The physical adequacy of the obtained solutions to existing
concepts about possible cosmological scenarios is demonstrated. The
gravitational vacuum condensate is shown to be a cosmological evolution factor.Comment: LaTeX, 14 pages, to be published in Int. J. Mod. Phys.
Re-entrant resonant tunneling
We study the effect of electron-electron interactions on the
resonant-tunneling spectroscopy of the localized states in a barrier. Using a
simple model of three localized states, we show that, due to the Coulomb
interactions, a single state can give rise to two resonant peaks in the
conductance as a function of gate voltage, G(Vg). We also demonstrate that an
additional higher-order resonance with Vg-position in between these two peaks
becomes possibile when interactions are taken into account. The corresponding
resonant-tunneling process involves two-electron transitions. We have observed
both these effects in GaAs transistor microstructures by studying the time
evolution of three adjacent G(Vg) peaks caused by fluctuating occupation of an
isolated impurity (modulator). The heights of the two stronger peaks exibit
in-phase fluctuations. The phase of fluctuations of the smaller middle peak is
opposite. The two stronger peaks have their origin in the same localized state,
and the third one corresponds to a co-tunneling process.Comment: 9 pages, REVTeX, 4 figure
Anisotropy and inflation in Bianchi I brane worlds
After a more general assumption on the influence of the bulk on the brane, we
extend some conclusions by Maartens et al. and Santos et al. on the asymptotic
behavior of Bianchi I brane worlds. As a consequence of the nonlocal
anisotropic stresses induced by the bulk, in most of our models, the brane does
not isotropize and the nonlocal energy does not vanish in the limit in which
the mean radius goes to infinity. We have also found the intriguing possibility
that the inflation due to the cosmological constant might be prevented by the
interaction with the bulk. We show that the problem for the mean radius can be
completely solved in our models, which include as particular cases those in the
references above.Comment: 10 pages, improved discussion on the likeliness of
non-isotropization, completed list of references, matches version to appear
in Class. Quantum Gra
INTEGRAL upper limits on gamma-ray emission associated with the gravitational wave event GW150914
Using observations of the INTErnational Gamma-Ray Astrophysics Laboratory
(INTEGRAL), we put upper limits on the gamma-ray and hard X-ray prompt emission
associated with the gravitational wave event GW150914, discovered by the
LIGO/Virgo collaboration. The omni-directional view of the INTEGRAL/SPI-ACS has
allowed us to constrain the fraction of energy emitted in the hard X-ray
electromagnetic component for the full high-probability sky region of LIGO
trigger. Our upper limits on the hard X-ray fluence at the time of the event
range from erg cm to
erg cm in the 75 keV - 2 MeV energy range for typical spectral models.
Our results constrain the ratio of the energy promptly released in gamma-rays
in the direction of the observer to the gravitational wave energy
EE. We discuss the implication of gamma-ray
limits on the characteristics of the gravitational wave source, based on the
available predictions for prompt electromagnetic emission.Comment: accepted for publication in ApJ
Linear in-plane magnetoconductance and spin susceptibility of a 2D electron gas on a vicinal silicon surface
In this work we have studied the parallel magnetoresistance of a 2DEG near a
vicinal silicon surface. An unusual, linear magnetoconductance is observed in
the fields up to T, which we explain by the effect of spin olarization
on impurity scattering. This linear magnetoresistance shows strong anomalies
near the boundaries of the minigap in the electron spectrum of the vicinal
system.Comment: (accepted to Phys. Rev. B
Quantum geometrodynamics creates new problems
The development of last years in quantum geometrodynamics highlights new
problems which were not obvious in its first formulation proposed by Wheeler
and DeWitt. At the first stage the main task was to apply known quantization
schemes to gravitational field or a certain cosmological model. This way has
led to the realization of the fact that a quantum description of the Universe
is impossible without implicit or explicit indication to a reference frame
presented by some medium, filling the whole Universe, with its own equation of
state and thermodynamical properties. Thus the questions arise, should one seek
for a "privileged" reference frame or consider all the variety of gauge
conditions and appropriate solutions for the wave function? It is worth noting
that thermodynamical properties of such a quantum Universe would also depend on
a chosen reference frame to some extent. So, we need a self-consistent quantum
theoretical and thermodynamical description of the Universe.Comment: 5 pages, talk presented at the XIII Russian Gravitational Conference,
Moscow, June 2008, a reference correcte
Brane-world Cosmologies with non-local bulk effects
It is very common to ignore the non-local bulk effects in the study of
brane-world cosmologies using the brane-world approach. However, we shall
illustrate through the use of three different scenarios, that the non-local
bulk-effect does indeed have significant impact on both the
initial and future behaviour of brane-world cosmologies.Comment: 17 pages, no figures, iopart.cls, submitted to CQ
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