207 research outputs found
Spooky black holes : gravitational self energy and space curvature
It is shown that space curvature can be disposed of by properly taking into
account gravitational self energies. This leads to a parameter free
modification of Newton's law, violating Gauss theorem, which accounts for the
crucial tests of gravitation in a flat space. Strong gravitational fields
entail opposing big gravitational self energies. The negative gravitational
self energy of a gravitational composite object, which results in a mass defect
with respect to the sum of the constituents, thus cancels out the latter at the
Schwarzschild radius. Hence a black hole, possible end result of the radiative
shrinkage of a star, having zero total energy cannot any longer interact with
other objects. Baryon number non conservation may result
Black holes and Higgs stability
We study the effect of primordial black holes on the classical rate of
nucleation of AdS regions within the standard electroweak vacuum. We find that
the energy barrier for transitions to the new vacuum, which characterizes the
exponential suppression of the nucleation rate, can be reduced significantly in
the black-hole background. A precise analysis is required in order to determine
whether the the existence of primordial black holes is compatible with the form
of the Higgs potential at high temperature or density in the Standard Model or
its extensions.Comment: 27 pages, 10 figures, conclusions expanded, to appear in JCA
Convective plan-form two-scale dynamos in a plane layer
We study generation of magnetic fields, involving large spatial scales, by
convective plan-forms in a horizontal layer. Magnetic modes and their growth
rates are expanded in power series in the scale ratio, and the magnetic eddy
diffusivity (MED) tensor is derived for flows, symmetric about the vertical
axis in a layer. For convective rolls magnetic eddy correction is demonstrated
to be always positive. For rectangular cell patterns, the region in the
parameter space of negative MED coincides with that of small-scale magnetic
field generation. No instances of negative MED in hexagonal cells are found. A
family of plan-forms with a smaller symmetry group than that of rectangular
cell patterns has been found numerically, where MED is negative for molecular
magnetic diffusivity over the threshold for the onset of small-scale magnetic
field generation.Comment: Latex. 24 pages with 3 Postscript figures, 19 references. Final
version (expanded Appendix 2, 4 references added, notation changed to a more
"user-friendly"), accepted in Geophysical and Astrophysical Fluid Dynamic
Some Unique Constants Associated with Extremal Black Holes
In recent papers we had developed a unified picture of black hole entropy and
curvature which was shown to lead to Hawking radiation. It was shown that for
any black hole mass, holography implies a phase space of just one quantum
associated with the interior of the black hole. Here we study extremal rotating
and charged black holes and obtain unique values for ratios of angular momentum
to entropy, charge to entropy, etc. It turns out that these ratios can be
expressed in terms of fundamental constants in nature, having analogies with
other physical systems, like in condensed matter physics.Comment: "Accepted for publication in Astrophysics & Space Science" 4 pages,
10 equation
On the spatial distribution of dark matter halos
We study the spatial distribution of dark matter halos in the Universe in
terms of their number density contrast, related to the underlying dark matter
fluctuation via a non-local and non-linear bias random field. The description
of the matter dynamics is simplified by adopting the `truncated' Zel'dovich
approximation to obtain both analytical results and simulated maps. The halo
number density field in our maps and its probability distribution reproduce
with excellent accuracy those of halos in a high-resolution N-body simulation
with the same initial conditions. Our non-linear and non-local bias
prescription matches the N-body halo distribution better than any Eulerian
linear and local bias.Comment: 4 pages, LaTeX (uses emulateapj; included psfig.tex), 3 figures, 1
table. Shortened version, matching the size requirements of ApJ Letters.
Accepted for publicatio
Energy composition of the Universe: time-independent internal symmetry
The energy composition of the Universe, as emerged from the Type Ia supernova
observations and the WMAP data, looks preposterously complex, -- but only at
the first glance. In fact, its structure proves to be simple and regular. An
analysis in terms of the Friedmann integral enables to recognize a remarkably
simple time-independent covariant robust recipe of the cosmic mix: the
numerical values of the Friedmann integral for vacuum, dark matter, baryons and
radiation are approximately identical. The identity may be treated as a
symmetry relation that unifies cosmic energies into a regular set, a quartet,
with the Friedmann integral as its common genuine time-independent physical
parameter. Such cosmic internal (non-geometrical) symmetry exists whenever
cosmic energies themselves exist in nature. It is most natural for a finite
Universe suggested by the WMAP data. A link to fundamental theory may be found
under the assumption about a special significance of the electroweak energy
scale in both particle physics and cosmology. A freeze-out model developed on
this basis demonstrates that the physical nature of new symmetry might be due
to the interplay between electroweak physics and gravity at the cosmic age of a
few picoseconds. The big `hierarchy number' of particle physics represents the
interplay in the model. This number quantifies the Friedmann integral and gives
also a measure to some other basic cosmological figures and phenomena
associated with new symmetry. In this way, cosmic internal symmetry provides a
common ground for better understanding of old and recent problems that
otherwise seem unrelated; the coincidence of the observed cosmic densities, the
flatness of the co-moving space, the initial perturbations and their amplitude,
the cosmic entropy are among them.Comment: 32 page
CDM Accelerating Cosmology as an Alternative to LCDM model
A new accelerating cosmology driven only by baryons plus cold dark matter
(CDM) is proposed in the framework of general relativity. In this model the
present accelerating stage of the Universe is powered by the negative pressure
describing the gravitationally-induced particle production of cold dark matter
particles. This kind of scenario has only one free parameter and the
differential equation governing the evolution of the scale factor is exactly
the same of the CDM model. For a spatially flat Universe, as predicted
by inflation (), it is found that the
effectively observed matter density parameter is ,
where is the constant parameter specifying the CDM particle creation
rate. The supernovae test based on the Union data (2008) requires so that as independently derived from weak
gravitational lensing, the large scale structure and other complementary
observations.Comment: 6 pages, 3 figure
Pdf's of Derivatives and Increments for Decaying Burgers Turbulence
A Lagrangian method is used to show that the power-law with a -7/2 exponent
in the negative tail of the pdf of the velocity gradient and of velocity
increments, predicted by E, Khanin, Mazel and Sinai (1997 Phys. Rev. Lett. 78,
1904) for forced Burgers turbulence, is also present in the unforced case. The
theory is extended to the second-order space derivative whose pdf has power-law
tails with exponent -2 at both large positive and negative values and to the
time derivatives. Pdf's of space and time derivatives have the same
(asymptotic) functional forms. This is interpreted in terms of a "random Taylor
hypothesis".Comment: LATEX 8 pages, 3 figures, to appear in Phys. Rev.
Cosmological Implications of Neutrinos
The lectures describe several cosmological effects produced by neutrinos.
Upper and lower cosmological limits on neutrino mass are derived. The role that
neutrinos may play in formation of large scale structure of the universe is
described and neutrino mass limits are presented. Effects of neutrinos on
cosmological background radiation and on big bang nucleosynthesis are
discussed. Limits on the number of neutrino flavors and mass/mixing are given.Comment: 41 page, 7 figures; lectures presented at ITEP Winter School,
February, 2002; to be published in the Proceeding
Black holes as antimatter factories
We consider accretion of matter onto a low mass black hole surrounded by
ionized medium. We show that, because of higher mobility of protons than
electrons, the black hole would acquire positive electric charge. If the black
hole's mass is about or below g, the electric field at the horizon
can reach the critical value which leads to vacuum instability and
electron--positron pair production by the Schwinger mechanism. Since the
positrons are ejected by the emergent electric field, while electrons are
back--captured, the black hole operates as an antimatter factory which
effectively converts protons into positrons.Comment: 5 pages, no figure. v2: with discussion section not included in the
refereed versio
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