98 research outputs found
Simulation of Transitions between "Pasta" Phases in Dense Matter
Calculations of equilibrium properties of dense matter predict that at
subnuclear densities nuclei can be rodlike or slablike. To investigate whether
transitions between phases with non-spherical nuclei can occur during the
collapse of a star, we perform quantum molecular dynamic simulations of the
compression of dense matter. We have succeeded in simulating the transitions
between rodlike and slablike nuclei and between slablike nuclei and cylindrical
bubbles. Our results strongly suggest that non-spherical nuclei can be formed
in the inner cores of collapsing stars.Comment: 4 pages, 4 figures, final version published in Phys. Rev. Lett.,
high-res figures can be seen at http://www.nordita.dk/~gentaro/research/fig
Massive Decaying Tau Neutrino and Big Bang Nucleosynthesis
Comparing Big Bang Nucleosynthesis predictions with the light element
abundances inferred from observational data, we can obtain the strong
constraints on some neutrino properties, e.g. number of neutrino species, mass,
lifetime. Recently the deuterium abundances were measured in high red-shift QSO
absorption systems. It is expected that they are close to the primordial
values, however, two groups have reported inconsistent values which are
different in one order of magnitude. In this paper we show how we can constrain
on neutrino mass and its lifetime in each case when we adopt either high
or low deuterium data. We find that if 0.01 \sec
\lesssim \tau_{\nutau} \lesssim 1 \sec and 10\mev \lesssim m_{\nutau}
\lesssim 24\mev, the theoretical predictions agree with the low D/H
abundances. On the other hand if we adopt the high D/H abundances, we obtain
the upper bound of neutrino mass, m_{\nutau}\lesssim 20 \mev.Comment: 11 pages, using LATEX and four postscript figure
R-Process Nucleosynthesis in MHD Jet Explosions of Core-Collapse Supernovae
We investigate -process nucleosynthesis during the magnetohydrodynamical
(MHD) explosion of supernova in a massive star of 13 . Contrary to
the case of the spherical explosion, jet-like explosion due to the combined
effects of the rotation and magnetic field lowers the electron fraction
significantly inside the layers above the iron core. We find that the ejected
material of low electron fraction responsible for the -process comes out
from the silicon rich layer of the presupernova model. This leads to the
production up to the third peak in the solar -process elements. We examine
whether the fission affects the -process paths by using the full nuclear
reaction network with both the spontaneous and -delayed fission
included. Moreover, we pay particular attention how the mass formula affects
the -process peaks with use of two mass formulae. It is found that both
formulae can reproduce the global abundance pattern up to the third peak though
detailed distributions are rather different. We point out that there are
variations in the -process nucleosynthesis if the MHD effects play an
important role in the supernova explosion.Comment: 19 pages with 7 figures, submitted to Ap
Effects of Neutrino Oscillation on the Supernova Neutrino Spectrum
The effects of three-flavor neutrino oscillation on the supernova neutrino
spectrum are studied. We calculate the expected event rate and energy spectra,
and their time evolution at the Superkamiokande (SK) and the Sudbury Neutrino
Observatory (SNO), by using a realistic neutrino burst model based on numerical
simulations of supernova explosions. We also employ a realistic density profile
based on a presupernova model for the calculation of neutrino conversion
probability in supernova envelopes. These realistic models and numerical
calculations allow us to quantitatively estimate the effects of neutrino
oscillation in a more realistic way than previous studies. We then found that
the degeneracy of the solutions of the solar neutrino problem can be broken by
the combination of the SK and SNO detections of a future Galactic supernova.Comment: 10 pages, 14 figures, corrected versio
Microscopic Study of Slablike and Rodlike Nuclei: Quantum Molecular Dynamics Approach
Structure of cold dense matter at subnuclear densities is investigated by
quantum molecular dynamics (QMD) simulations. We succeeded in showing that the
phases with slab-like and rod-like nuclei etc. can be formed dynamically from
hot uniform nuclear matter without any assumptions on nuclear shape. We also
observe intermediate phases, which has complicated nuclear shapes. Geometrical
structures of matter are analyzed with Minkowski functionals, and it is found
out that intermediate phases can be characterized as ones with negative Euler
characteristic. Our result suggests the existence of these kinds of phases in
addition to the simple ``pasta'' phases in neutron star crusts.Comment: 6 pages, 4 figures, RevTex4; to be published in Phys. Rev. C Rapid
Communication (accepted version
Supernova Neutrinos, Neutrino Oscillations, and the Mass of the Progenitor Star
We investigate the initial progenitor mass dependence of the early-phase
neutrino signal from supernovae taking neutrino oscillations into account. The
early-phase analysis has advantages in that it is not affected by the time
evolution of the density structure of the star due to shock propagation or
whether the remnant is a neutron star or a black hole. The initial mass affects
the evolution of the massive star and its presupernova structure, which is
important for two reasons when considering the neutrino signal. First, the
density profile of the mantle affects the dynamics of neutrino oscillation in
supernova. Second, the final iron core structure determines the features of the
neutrino burst, i.e., the luminosity and the average energy. We find that both
effects are rather small. This is desirable when we try to extract information
on neutrino parameters from future supernova-neutrino observations. Although
the uncertainty due to the progenitor mass is not small for intermediate
(), we
can, nevertheless, determine the character of the mass hierarchy and whether
is very large or very small.Comment: 8 pages, 15 figure
Evolution Equation of Phenotype Distribution: General Formulation and Application to Error Catastrophe
An equation describing the evolution of phenotypic distribution is derived
using methods developed in statistical physics. The equation is solved by using
the singular perturbation method, and assuming that the number of bases in the
genetic sequence is large. Applying the equation to the mutation-selection
model by Eigen provides the critical mutation rate for the error catastrophe.
Phenotypic fluctuation of clones (individuals sharing the same gene) is
introduced into this evolution equation. With this formalism, it is found that
the critical mutation rate is sometimes increased by the phenotypic
fluctuations, i.e., noise can enhance robustness of a fitted state to mutation.
Our formalism is systematic and general, while approximations to derive more
tractable evolution equations are also discussed.Comment: 22 pages, 2 figure
A comprehensive study of neutrino spin-flavour conversion in supernovae and the neutrino mass hierarchy
Resonant spin-flavour (RSF) conversions of supernova neutrinos, which is
induced by the interaction between the nonzero neutrino magnetic moment and
supernova magnetic fields, are studied for both normal and inverted mass
hierarchy. As the case for the pure matter-induced neutrino oscillation
(Mikheyev--Smirnov--Wolfenstein (MSW) effect), we find that the RSF transitions
are strongly dependent on the neutrino mass hierarchy as well as the value of
. Flavour conversions are solved numerically for various neutrino
parameter sets, with presupernova profile calculated by Woosley and Weaver. In
particular, it is very interesting that the RSF-induced
\nu_\rme\to\bar\nu_\rme transition occurs, if the following conditions are
all satisfied: the value of ( is the neutrino magnetic
moment, and is the magnetic field strength) is sufficiently strong, the
neutrino mass hierarchy is inverted, and the value of is large
enough to induce adiabatic MSW resonance. In this case, the strong peak due to
original \nu_\rme emitted from neutronization burst would exist in time
profile of the neutrino events detected at the Super-Kamiokande detector. If
this peak were observed in reality, it would provide fruitful information on
the neutrino properties. On the other hand, characters of the neutrino spectra
are also different between the neutrino models, but we find that there remains
degeneracy among several models. Dependence on presupernova models is also
discussed.Comment: 23 pages, 11 figures, corrected minor typos, added references. Final
version to appear in Journal of Cosmology and Astroparticle Physic
Big Bang Nucleosynthesis and Lepton Number Asymmetry in the Universe
Recently it is reported that there is the discrepancy between big bang
nucleosynthesis theory and observations (BBN crisis). We show that BBN
predictions agree with the primordial abundances of light elements, He4, D, He3
and Li7 inferred from the observational data if an electron neutrino has a net
chemical potential xi_{nu_e} due to lepton asymmetry. We estimate that
xi_{nu_e} = 0.043^{+0.040}_{-0.040} (95% C.L.) and Omega_bh^2 =
0.015^{+0.006}_{-0.003} (95% C.L.).Comment: 10 pages, using AAS LATEX and three postscript figure
Mass spectrum of primordial black holes from inflationary perturbation in the Randall-Sundrum braneworld: a limit on blue spectra
The mass spectrum of the primordial black holes formed by density
perturbation in the radiation-dominated era of the Randall-Sundrum type-2
cosmology is given. The spectrum coincides with standard four-dimensional one
on large scales but the deviation is apparent on smaller scales. The mass
spectrum is initially softer than standard four-dimensional one, while after
accretion during the earliest era it becomes harder than that. We also show
expected extragalactic diffuse photon background spectra varying the initial
perturbation power-law power spectrum and give constraints on the blue spectra
and/or the reheating temperature. The most recent observations on the small
scale density perturbation from WMAP, SDSS and Lyman-\alpha Forest are used.
What we get are interpreted as constraints on the smaller scale inflation on
the brane connected to the larger one at the scale of Lyman-\alpha Forest. If
we set the bulk curvature radius to be 0.1 mm and assume the reheating
temperature is higher than 10^6 GeV, the scalar spectral index from the smaller
scale inflation is constrained to be n \lesssim 1.3. Typically, the constraints
are tighter than standard four-dimensional one, which is also revised by us
using the most recent observations.Comment: 19 pages, 6 figures; typos corrected, references added, published in
JCA
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