345 research outputs found
Active Galactic Nuclei and Transformation of Dark Matter into Visible Matter
The hypothesis that dark matter is converted into visible particles in active
galactic nuclei is investigated. If dark matter consists of stable superheavy
neutral particles and active galactic nuclei are rotating black holes, then,
due to the Penrose process, superheavy particles can decay into unstable
particles with larger mass, whose decay into quarks and leptons leads to events
in cosmic rays observed by the Auger group. Similar processes of decay of
superheavy particles of dark matter into visible matter occurred in the early
Universe. Numerical estimates of the processes in active galactic nuclei and in
the early Universe are given.Comment: 5 pages, LaTeX; v2: one reference added, published versio
Interactions of oblique interplanetary discontinuities and their manifestations during STIP intervals 15-19
The generation of slow shock waves as the result of the interaction of Alfven discontinuities with solar wind contact surfaces is considered. The latter are taken to be the boundaries of proton and alpha-particle concentration inhomogeneities. It is found that the intensity of the Alfven discontinuity may be increased as the result of its interaction with the more dense plasma. The converse (i.e., decrease of the Alfven discontinuity's intensity following interaction with a less dense plasma) is also indicated. Also discussed is the generation of a magnetic cloud as the result of the interaction of a quasi-parallel Alfven discontinuity with a dense plasma contact surface. It is shown that the (solar-generated) Alfven discontinuity may then be transformed into non-flare fast and slow shock waves as the result of this interaction. Thus, it is indicated that some fast shock waves in the solar wind may have a nonsolar origin
Particles with negative energies in black holes
The problem of the existence of particles with negative energies inside and
outside of Schwarzschild, charged and rotating black holes is investigated.
Different definitions of the energy of the particle inside the Schwarzschild
black hole are analyzed and it is shown in what cases this energy can be
negative. A comparison is made for the cases of rotating black holes described
by the Kerr metric when the energy of the particle can be negative in the
ergosphere and the Reissner-Nordstrom metric.Comment: 10 pages, 2 figures, typos correction to match published versio
On collisions with unlimited energies in the vicinity of Kerr and Schwarzschild black hole horizons
Two particle collisions close to the horizon of the rotating nonextremal
Kerr's and Schwarzschild black holes are analyzed. For the case of multiple
collisions it is shown that high energy in the centre of mass frame occurs due
to a great relative velocity of two particles and a large Lorentz factor. The
dependence of the relative velocity on the distance to horizon is analyzed, the
time of movement from the point in the accretion disc to the point of
scattering with large energy as well as the time of back movement to the Earth
are calculated. It is shown that they have reasonable order.Comment: 6 pages, 1 figure. arXiv admin note: significant text overlap with
arXiv:1105.154
Space-Time Description of Scalar Particle Creation by a Homogeneous Isotropic Gravitational Field
We give the generalization of the method of the space-time description of
particle creation by a gravitational field for a scalar field with nonconformal
coupling to the curvature. The space-time correlation function is obtained for
a created pair of the quasi-particles, corresponding to a diagonal form of the
instantaneous Hamiltonian. The case of an adiabatic change of the metric of
homogeneous isotropic space is analyzed. We show that the created pairs of
quasi-particles in de Sitter space should be interpreted as pairs of virtual
particles.Comment: 7 pages, 3 figure
Hamiltonian approach to the dynamical Casimir effect
A Hamiltonian approach is introduced in order to address some severe problems
associated with the physical description of the dynamical Casimir effect at all
times. For simplicity, the case of a neutral scalar field in a one-dimensional
cavity with partially transmitting mirrors (an essential proviso) is
considered, but the method can be extended to fields of any kind and higher
dimensions. The motional force calculated in our approach contains a reactive
term --proportional to the mirrors' acceleration-- which is fundamental in
order to obtain (quasi)particles with a positive energy all the time during the
movement of the mirrors --while always satisfying the energy conservation law.
Comparisons with other approaches and a careful analysis of the interrelations
among the different results previously obtained in the literature are carried
out.Comment: 4 pages, no figures; version published in Phys. Rev. Lett. 97 (2006)
13040
The speed of gravity in general relativity
The question is discussed of what is the speed of gravity (at the fundamental
non-perturbative level). The question is important, if nowhere else, in
discussing the problem of information "lost" in black holes. It turns out that
the duly defined "gravitational signal" generally may be causal, superluminal
and "semi-superluminal". In the class of globally hyperbolic spacetimes the two
last varieties coincide. And if some (often imposed, but not always satisfied)
conditions hold, the signals may be \emph{only} causal. In this sense the speed
of gravity does not exceed the speed of light.Comment: typos corrected, et
Graphene tests of Klein phenomena
Graphene is characterized by chiral electronic excitations. As such it
provides a perfect testing ground for the production of Klein pairs
(electron/holes). If confirmed, the standard results for barrier phenomena must
be reconsidered with, as a byproduct, the accumulation within the barrier of
holes.Comment: 8 page
Spontaneous symmetry breaking for long-wave gravitons in the early Universe
It is shown that nonlinear terms in equations of gravitons on the background
of curved space-time of the expanding Universe can solve the problem of the
negative square of the effective mass formally arising in linear approximation
for gravitons. Similar to well known spontaneous breaking of symmetry in
Goldstone model one must take another vacuum so that nonzero vacuum expectation
value of the quantized graviton field leads to change of spectrum for
gravitons. There appears two graviton fields, one with the positive mass,
another with the zero mass. Energy density and the density of particles created
by gravitation of the expanding Universe are calculated for some special cases
of the scale factor. Numerical results are obtained for the dust universe case.Comment: 13 page
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