8,688 research outputs found
Gravitational Wave Bursts from Collisions of Primordial Black Holes in Clusters
The rate of gravitational wave bursts from the mergers of massive primordial
black holes in clusters is calculated. Such clusters of black holes can be
formed through phase transitions in the early Universe. The central black holes
in clusters can serve as the seeds of supermassive black holes in galactic
nuclei. The expected burst detection rate by the LISA gravitational wave
detector is estimated.Comment: 10 pages, 2 figure
Regiodivergent condensation of 5-alkoxycarbonyl-1H-pyrrol-2,3-diones with cyclic ketazinones en route to spirocyclic scaffolds
The condensation of 5-alkoxycarbonyl-1H-pyrrolediones with cyclic ketazinones was systematically investigated. It was discovered that the regioselectivity of this reaction can be easily swapped between two alternative directions affording derivatives of partially hydrogenated indole or benzofurane. The control of this regioselectivity is efficiently governed by steric effects at the hydrazone moiety of the ketazinone reagent
Mechanism for the Suppression of Intermediate-Mass Black Holes
A model for the formation of supermassive primordial black holes in galactic
nuclei with the simultaneous suppression of the formation of intermediate-mass
black holes is presented. A bimodal mass function for black holes formed
through phase transitions in a model with a "Mexican hat" potential has been
found. The classical motion of the phase of a complex scalar field during
inflation has been taken into account. Possible observational manifestations of
primordial black holes in galaxies and constraints on their number are
discussed.Comment: 12 pages, 2 figure
Multidimensional world, inflation and modern acceleration
Starting from pure multidimensional gravity with curvature-nonlinear terms
but no matter fields in the initial action, we obtain a cosmological model with
two effective scalar fields related to the size of two extra factor spaces. The
model includes both an early inflationary stage and that of modern accelerated
expansion and satisfies the observational data. There are no small parameters;
the effective inflaton mass depends on the initial conditions which explain its
small value as compared to the Planck mass. At the modern stage, the size of
extra dimensions slowly increases, therefore this model predicts drastic
changes in the physical laws of our Universe in the remote future.Comment: 7 two-column revtex pages, 2 figure
Sensitivity of synchrotron radiation to the superthermal electron population in mildly relativistic plasma
Synchrotron radiation has markedly different behavior in and in plasma. We show that
high-energy electrons which occupy the tail of velocity distribution function
have disproportionate impact on power loss of plasma.
If electrons with energy more than a cutoff energy are redistributed while
keeping the Maxwellian distribution function below cutoff energy intact, both
emission and absorption of synchrotron radiation act to decrease the lost
power. These novel radiation transport effects in non-equilibrium plasma
suggest large utility in the deconfinement of high-energy electrons to reduce
synchrotron radiation in applications where the radiation is deleterious.Comment: 6 pages, 5 figures, submitted to Po
Self-stabilization of extra dimensions
We show that the problem of stabilization of extra dimensions in Kaluza-Klein
type cosmology may be solved in a theory of gravity involving high-order
curvature invariants. The method suggested (employing a slow-change
approximation) can work with rather a general form of the gravitational action.
As examples, we consider pure gravity with Lagrangians quadratic and cubic in
the scalar curvature and some more complex ones in a simple Kaluza-Klein
framework. After a transition to the 4D Einstein conformal frame, this results
in effective scalar field theories with certain effective potentials, which in
many cases possess positive minima providing stable small-size extra
dimensions. Estimates made in the original (Jordan) conformal frame show that
the problem of a small value of the cosmological constant in the present
Universe is softened in this framework but is not solved completely.}Comment: 10 pages, 4 figures, revtex4. Version with additions and corrections,
accepted at Phys. Rev.
Hall Effect in the coma of 67P/Churyumov-Gerasimenko
Magnetohydrodynamics simulations have been carried out in studying the solar
wind and cometary plasma interactions for decades. Various plasma boundaries
have been simulated and compared well with observations for comet 1P/Halley.
The Rosetta mission, which studies comet 67P/Churyumov-Gerasimenko, challenges
our understanding of the solar wind and comet interactions. The Rosetta Plasma
Consortium observed regions of very weak magnetic field outside the predicted
diamagnetic cavity. In this paper, we simulate the inner coma with the Hall
magnetohydrodynamics equations and show that the Hall effect is important in
the inner coma environment. The magnetic field topology becomes complex and
magnetic reconnection occurs on the dayside when the Hall effect is taken into
account. The magnetic reconnection on the dayside can generate weak magnetic
filed regions outside the global diamagnetic cavity, which may explain the
Rosetta Plasma Consortium observations. We conclude that the substantial change
in the inner coma environment is due to the fact that the ion inertial length
(or gyro radius) is not much smaller than the size of the diamagnetic cavity.Comment: 23 pages, 6 figur
Heat-kernel Coefficients and Spectra of the Vector Laplacians on Spherical Domains with Conical Singularities
The spherical domains with conical singularities are a convenient
arena for studying the properties of tensor Laplacians on arbitrary manifolds
with such a kind of singular points. In this paper the vector Laplacian on
is considered and its spectrum is calculated exactly for any
dimension . This enables one to find the Schwinger-DeWitt coefficients of
this operator by using the residues of the -function. In particular, the
second coefficient, defining the conformal anomaly, is explicitly calculated on
and its generalization to arbitrary manifolds is found. As an
application of this result, the standard renormalization of the one-loop
effective action of gauge fields is demonstrated to be sufficient to remove the
ultraviolet divergences up to the first order in the conical deficit angle.Comment: plain LaTeX, 23 pp., revised version, a misprint in expressions (1.8)
and (4.38) of the second heat coefficient for the vector Laplacian is
corrected. No other change
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