961 research outputs found
Radiation from hot bare strange stars
We present the results of numerical simulations of stationary, spherically
outflowing, pair winds, with total luminosities of L=10^{35}- 10^{42} ergs/s.
These results have direct relevance to the emission from hot, bare, strange
stars, which are thought to be powerful sources of electron-positron pairs
created by the Coulomb barrier at the quark surface. The spectra of emergent
photons and pairs are calculated. For L > 2x10^{35} erg/s, photons dominate the
emerging emission. As L increases from 10^{35} to 10^{42} ergs/s, the mean
photon energy decreases from ~ 400-500 keV to 40 keV, while the spectrum
changes in shape from a wide annihilation line to being nearly blackbody with a
high energy (> 100 keV) tail. Such a correlation of the photon spectrum with
the luminosity, together with the fact that super-Eddington luminosities can be
achieved, might be a good observational signature of hot, bare, strange stars.Comment: 4 pages, 4 figures, Accepted in MNRAS, includes minor correction
Pair Winds in Schwarzschild Spacetime with Application to Strange Stars
We present the results of numerical simulations of stationary, spherically
outflowing, electron-positron pair winds, with total luminosities in the range
10^{34}--10^{42} ergs/s. In the concrete example described here, the wind
injection source is a hot, bare, strange star, predicted to be a powerful
source of pairs created by the Coulomb barrier at the quark surface. We find
that photons dominate in the emerging emission, and the emerging photon
spectrum is rather hard and differs substantially from the thermal spectrum
expected from a neutron star with the same luminosity. This might help
distinguish the putative bare strange stars from neutron stars.Comment: 3 pages, 2 figures, Invited talk at 11th Marcel Grossmann Meeting,
Berlin, July 200
Feasibility of study magnetic proximity effects in bilayer "superconductor/ferromagnet" using waveguide-enhanced Polarized Neutron Reflectometry
A resonant enhancement of the neutron standing waves is proposed to use in
order to increase the magnetic neutron scattering from a
"superconductor/ferromagnet"(S/F) bilayer. The model calculations show that
usage of this effect allows to increase the magnetic scattering intensity by
factor of hundreds. Aspects related to the growth procedure (order of
deposition, roughness of the layers etc) as well as experimental conditions
(resolution, polarization of the neutron beam, background etc) are also
discussed.
Collected experimental data for the S/F heterostructure
Cu(32nm)/V(40nm)/Fe(1nm)/MgO confirmed the presence of a resonant 60-fold
amplification of the magnetic scattering.Comment: The manuscript of the article submitted to Crysstalography Reports.
23 pages, 5 figure
Convergence Acceleration Techniques
This work describes numerical methods that are useful in many areas: examples
include statistical modelling (bioinformatics, computational biology),
theoretical physics, and even pure mathematics. The methods are primarily
useful for the acceleration of slowly convergent and the summation of divergent
series that are ubiquitous in relevant applications. The computing time is
reduced in many cases by orders of magnitude.Comment: 6 pages, LaTeX; provides an easy-to-understand introduction to the
field of convergence acceleratio
GRBs and the thermalization process of electron-positron plasmas
We discuss the temporal evolution of the pair plasma created in Gamma-Ray
Burst sources. A particular attention is paid to the relaxation of the plasma
into thermal equilibrium. We also discuss the connection between the dynamics
of expansion and the spatial geometry of the plasma. The role of the baryonic
loading parameter is emphasized.Comment: 4 pages, 3 figures, in the Proceedings of the "Gamma Ray Bursts 2007"
meeting, November 5-9, 2007, Santa Fe, New Mexico, US
Effect of local Coulomb interaction on Majorana corner modes: weak and strong correlation limits
Here we present an analysis of the evolution of Majorana corner modes
realizing in a higher-order topological superconductor (HOTSC) on a square
lattice under the influence of local Coulomb repulsion. The HOTSC spectral
properties were considered in two regimes: when the intensities of many-body
interactions are either weak or strong. The weak regime was studied using the
mean-field approximation with self-consistent solutions carried out both in the
uniform case and taking into account of the boundary of the finite
square-shaped system. It is shown that in the uniform case the topologically
nontrivial phase on the phase diagram is widened by the Coulomb repulsion. The
boundary effect, resulting in an inhomogeneous spatial distribution of the
correlators, leads to the appearance of the crossover from the symmetric
spin-independent solution to the spin-dependent one characterized by a
spontaneously broken symmetry. In the former the corner states have energies
that are determined by the overlap of the excitation wave functions localized
at the different corners. In the latter the corner excitation energy is defined
by the Coulomb repulsion intensity with a quadratic law. The crossover is a
finite size effect, i.e. the larger the system the lesser the critical value of
the Coulomb repulsion. In the strong repulsion regime we derive the effective
HOTSC Hamiltonian in the atomic representation and found a rich variety of
interactions induced by virtual processes between the lower and upper Hubbard
subbands. It is shown that Majorana corner modes still can be realized in the
limit of the infinite repulsion. Although the boundaries of the topologically
nontrivial phase are strongly renormalized by Hubbard corrections.Comment: 13 pages, 6 figure
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