6,375 research outputs found
Creation of the Nonconformal Scalar Particles in Nonstationary Metric
The nonconformal scalar field is considered in N-dimensional space-time with
metric which includes, in particular, the cases of nonhomogeneous spaces and
anisotropic spaces of Bianchi type-I. The modified Hamiltonian is constructed.
Under the diagonalization of it the energy of quasiparticles is equal to the
oscillator frequency of the wave equation. The density of particles created by
nonstationary metric is investigated. It is shown that the densities of
conformal and nonconformal particles created in Friedmann radiative-dominant
Universe coincide.Comment: LaTeX, 4 pages, no figure
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
Polarization of Thermal X-rays from Isolated Neutron Stars
Since the opacity of a magnetized plasma depends on polarization of
radiation, the radiation emergent from atmospheres of neutron stars with strong
magnetic fields is expected to be strongly polarized. The degree of linear
polarization, typically ~10-30%, depends on photon energy, effective
temperature and magnetic field. The spectrum of polarization is more sensitive
to the magnetic field than the spectrum of intensity. Both the degree of
polarization and the position angle vary with the neutron star rotation period
so that the shape of polarization pulse profiles depends on the orientation of
the rotational and magnetic axes. Moreover, as the polarization is
substantially modified by the general relativistic effects, observations of
polarization of X-ray radiation from isolated neutron stars provide a new
method for evaluating the mass-to-radius ratio of these objects, which is
particularly important for elucidating the properties of the superdense matter
in the neutron star interiors.Comment: 7 figures, to be published in Ap
Cold dark matter and primordial superheavy particles
The hypothesis that cold dark matter consists of primordial superheavy
particles, the decay of short lifetime component of which led to the observable
mass of matter while long living component survived up to modern times
manifesting its presence in high energetic cosmic rays particles is
investigated.Comment: LaTeX, 5 pages, no figure
Classification of integrable hydrodynamic chains and generating functions of conservation laws
New approach to classification of integrable hydrodynamic chains is
established. Generating functions of conservation laws are classified by the
method of hydrodynamic reductions. N parametric family of explicit hydrodynamic
reductions allows to reconstruct corresponding hydrodynamic chains. Plenty new
hydrodynamic chains are found
Atmospheres and Spectra of Strongly Magnetized Neutron Stars -- III. Partially Ionized Hydrogen Models
We construct partially ionized hydrogen atmosphere models for magnetized
neutron stars in radiative equilibrium with surface fields B=10^12-5 \times
10^14 G and effective temperatures T_eff \sim a few \times 10^5-10^6 K. These
models are based on the latest equation of state and opacity results for
magnetized, partially ionized hydrogen plasmas that take into account various
magnetic and dense medium effects. The atmospheres directly determine the
characteristics of thermal emission from isolated neutron stars. For the models
with B=10^12-10^13 G, the spectral features due to neutral atoms lie at extreme
UV and very soft X-ray energy bands and therefore are difficult to observe.
However, the continuum flux is also different from the fully ionized case,
especially at lower energies. For the superstrong field models (B\ga 10^14 G),
we show that the vacuum polarization effect not only suppresses the proton
cyclotron line as shown previously, but also suppresses spectral features due
to bound species; therefore spectral lines or features in thermal radiation are
more difficult to observe when the neutron star magnetic field is \ga 10^14 G.Comment: 12 pages, 10 figures; ApJ, accepted (v599: Dec 20, 2003
High-energy threshold reaction rates on 0.8 GeV proton-irradiated thick Pb-target
This works presents results of activation-aided determination of threshold
reaction rates in 92 209Bi, natPb, 197Au, 181Ta, 169Tm, natIn, 93Nb, 64Zn,
65Cu, 63Cu, 59Co, 19F, and 12C samples and in 121 27Al samples. All the samples
were aligned with the proton beam axis inside and outside the demountable 92-cm
thick Pb target of 15-cm diameter assembled of 23 4-cm thick discs. The samples
were placed on 12 target disks to reproduce the long axis distribution of
protons and neutrons. In June 2006, the target was exposed for 18 hours to a
800-MeV proton beam extracted from the ITEP U-10 accelerator. The proton
fluence and the proton beam shape were determined using the 27Al(p,x)7Be
monitor reaction. The reaction rates were determined by the direct
gamma-spectrometry techniques. In total, 1196 gamma-spectra have been measured,
and about 1500 reaction rates determined. The measured reaction rates were
simulated by the MCNPX code using the following databases: ENDF/B6 for neutrons
below 20 MeV, MENDL2 for 20-100 MeV neutrons, and MENDL2P for proton cross
sections up to 200 MeV. An acceptable agreement of simulations with
experimental data has been found.Comment: 4 pages, 5 figures, 3 tables, only pdf file, to be published in Proc.
Int. Conf. on Nucl. Data for Sci. and Technology (ND2007), Nice, France,
April 22-27, 200
Residual nuclide formation in 206,207,208,nat-Pb and 209-Bi induced by 0.04-2.6 GeV Protons as well as in 56-Fe induced by 0.3-2.6 GeV Protons
5972 independent and cumulative yields of radioactive residuals nuclei have
been measured in 55 thin 206,207,208,nat-Pb and 209-Bi targets irradiated by
0.04, 0.07, 0.10, 0.15, 0.25, 0.6, 0.8, 1.2, 1.4, 1.6, and 2.6 GeV protons.
Besides, 219 yields have been measured in 0.3, 0.5, 0.75, 1.0, 1.5, and 2.6 GeV
proton-irradiated 56-Fe target. The protons were extracted from the ITEP U-10
synchrotron. The measured data are compared with experimental results obtained
elsewhere and with theoretical calculations by LAHET, MCNPX, CEM03, LAQGSM03,
CASCADE, CASCADO, and LAHETO codes. The predictive power was found to be
different for each of the codes tested, but was satisfactory on the whole in
the case of spallation products. At the same time, none of the codes can
de-scribe well the product yields throughout the whole product mass range, and
all codes must be further improved.Comment: 4 pages, 4 figures, 2 tables, only pdf file, to be published in Proc.
Int. Conf. on Nucl. Data for Sci. and Technology (ND2007), Nice, France,
April 22-27, 20
Whitham systems and deformations
We consider the deformations of Whitham systems including the "dispersion
terms" and having the form of Dubrovin-Zhang deformations of Frobenius
manifolds. The procedure is connected with B.A. Dubrovin problem of
deformations of Frobenius manifolds corresponding to the Whitham systems of
integrable hierarchies. Under some non-degeneracy requirements we suggest a
general scheme of the deformation of the hyperbolic Whitham systems using the
initial non-linear system. The general form of the deformed Whitham system
coincides with the form of the "low-dispersion" asymptotic expansions used by
B.A. Dubrovin and Y. Zhang in the theory of deformations of Frobenius
manifolds.Comment: 27 pages, Late
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