24,216 research outputs found
Numerical Study on Stellar Core Collapse and Neutrino Emission: Probe into the Spherically Symmetric Black Hole Progenitors with 3 - 30Msun Iron Cores
The existence of various anomalous stars, such as the first stars in the
universe or stars produced by stellar mergers, has been recently proposed. Some
of these stars will result in black hole formation. In this study, we
investigate iron core collapse and black hole formation systematically for the
iron-core mass range of 3 - 30Msun, which has not been studied well so far.
Models used here are mostly isentropic iron cores that may be produced in
merged stars in the present universe but we also employ a model that is meant
for a Population III star and is obtained by evolutionary calculation. We solve
numerically the general relativistic hydrodynamics and neutrino transfer
equations simultaneously, treating neutrino reactions in detail under spherical
symmetry. As a result, we find that massive iron cores with ~10Msun
unexpectedly produce a bounce owing to the thermal pressure of nucleons before
black hole formation. The features of neutrino signals emitted from such
massive iron cores differ in time evolution and spectrum from those of ordinary
supernovae. Firstly, the neutronization burst is less remarkable or disappears
completely for more massive models because the density is lower at the bounce.
Secondly, the spectra of neutrinos, except the electron type, are softer owing
to the electron-positron pair creation before the bounce. We also study the
effects of the initial density profile, finding that the larger the initial
density gradient is, the more steeply the neutronization burst declines.
Further more, we suggest a way to probe into the black hole progenitors from
the neutrino emission and estimate the event number for the currently operating
neutrino detectors.Comment: 33 pages, 13 figures, accepted by Ap
Spin-dependent Rabi oscillations in single quantum=0D dot
Ultrafast optical pump of exciton resonance in single quantum dot by an
elliptically polarized laser pulse is described by the non-Markov balance
equations. Population and spin dynamics are investigated and spin-dependent
Rabi oscillations are considered for the case of a flat quantum dot, with the
lateral size greater than the height. The following peculiarities of temporal
evolution have been found: a) a beating of Rabi oscillations under an
elliptically polarized pump and b) quenching of spin orientation due to a
spin-orbit splitting effect.Comment: 4 pages, 3 figure
Light majoron cold dark matter from topological defects and the formation of boson stars
We show that for a relatively light majoron ( eV) non-thermal
production from topological defects is an efficient production mechanism.
Taking the type I seesaw as benchmark scheme, we estimate the primordial
majoron abundance and determine the required parameter choices where it can
account for the observed cosmological dark matter. The latter is consistent
with the scale of unification. Possible direct detection of light majorons with
future experiments such as PTOLEMY and the formation of boson stars from the
majoron dark matter are also discussed.Comment: 27 pages, 3 figures; v2: references added, matches published versio
Localization Properties of Electronic States in Polaron Model of poly(dG)-poly(dC) and poly(dA)-poly(dT) DNA polymers
We numerically investigate localization properties of electronic states in a
static model of poly(dG)-poly(dC) and poly(dA)-poly(dT) DNA polymers with
realistic parameters obtained by quantum-chemical calculation. The randomness
in the on-site energies caused by the electron-phonon coupling are completely
correlated to the off-diagonal parts. In the single electron model, the effect
of the hydrogen-bond stretchings, the twist angles between the base pairs and
the finite system size effects on the energy dependence of the localization
length and on the Lyapunov exponent are given. The localization length is
reduced by the influence of the fluctuations in the hydrogen bond stretchings.
It is also shown that the helical twist angle affects the localization length
in the poly(dG)-poly(dC) DNA polymer more strongly than in the
poly(dA)-poly(dT) one. Furthermore, we show resonance structures in the energy
dependence of the localization length when the system size is relatively small.Comment: 6 pages, 6 figure
Magnetic field-induced one-magnon Raman scattering in the magnon Bose-Einstein condensation phase of TlCuCl
We report the observation of the -symmetric one-magnon Raman peak
in the magnon Bose-Einstein condensation phase of TlCuCl. Its Raman shift
traces the one-magnon energy at the magnetic point, and its intensity
is proportional to the squared transverse magnetization. The appearance of the
one-magnon Raman scattering originates from the exchange magnon Raman process
and reflects the change of the magnetic-state symmetry. Using the bond-operator
representation, we theoretically clarify the Raman selection rules, being
consistent with the experimental results.Comment: 6 pages, 4 figure
An Implicit Lagrangean Code for Spherically Symmetric General Relativistic Hydrodynamics with an Approximate Riemann Solver
An implicit Lagrangian hydrodynamics code for general relativistic spherical
collapse is presented. This scheme is based on an approximate linearized
Riemann solver (Roe type scheme). This code is aimed especially at the
calculation of the late phase of collapse-driven supernovae and the nascent
neutron star, where there is a remarkable contrast between the dynamical time
scale of the proto-neutron star and the diffusion time scale of neutrinos,
without such severe limitation of the Courant condition at the center of the
neutron star. Several standard test calculations have been done. Two other
adiabatic simulations have also been done in order to test the performance of
the code in the context of the collapse-driven supernovae. It is found that the
time step can be extended far beyond the Courant limitation at the center of
the neutron star. The details of the scheme and the results of these test
calculations are discussed.Comment: AASTeX v4.0, 24 pages, 13 figures on request from
[email protected], submitted to Ap
- …