31,794 research outputs found

### Dynamics and neutrino signal of black hole formation in non-rotating failed supernovae. II. progenitor dependence

We study the progenitor dependence of the black hole formation and its
associated neutrino signals from the gravitational collapse of non-rotating
massive stars, following the preceding study on the single progenitor model in
Sumiyoshi et al. (2007). We aim to clarify whether the dynamical evolution
toward the black hole formation occurs in the same manner for different
progenitors and to examine whether the characteristic of neutrino bursts is
general having the short duration and the rapidly increasing average energies.
We perform the numerical simulations by general relativistic neutrino-radiation
hydrodynamics to follow the dynamical evolution from the collapse of
pre-supernova models of 40Msun and 50Msun toward the black hole formation via
contracting proto-neutron stars. For the three progenitor models studied in
this paper, we found that the black hole formation occurs in ~0.4-1.5 s after
core bounce through the increase of proto-neutron star mass together with the
short and energetic neutrino burst. We found that density profile of progenitor
is important to determine the accretion rate onto the proto-neutron star and,
therefore, the duration of neutrino burst. We compare the neutrino bursts of
black hole forming events from different progenitors and discuss whether we can
probe clearly the progenitor and/or the dense matter.Comment: 30 pages, 11 figures, accepted for publication in Ap

### Dynamics and neutrino signal of black hole formation in non-rotating failed supernovae. I. EOS dependence

We study the black hole formation and the neutrino signal from the
gravitational collapse of a non-rotating massive star of 40 Msun. Adopting two
different sets of realistic equation of state (EOS) of dense matter, we perform
the numerical simulations of general relativistic neutrino-radiation
hydrodynamics under the spherical symmetry. We make comparisons of the core
bounce, the shock propagation, the evolution of nascent proto-neutron star and
the resulting re-collapse to black hole to reveal the influence of EOS. We also
explore the influence of EOS on the neutrino emission during the evolution
toward the black hole formation. We find that the speed of contraction of the
nascent proto-neutron star, whose mass increases fast due to the intense
accretion, is different depending on the EOS and the resulting profiles of
density and temperature differ significantly. The black hole formation occurs
at 0.6-1.3 sec after bounce when the proto-neutron star exceeds its maximum
mass, which is crucially determined by the EOS. We find that the average
energies of neutrinos increase after bounce because of rapid temperature
increase, but at different speeds depending on the EOS. The duration of
neutrino emission up to the black hole formation is found different according
to the different timing of re-collapse. These characteristics of neutrino
signatures are distinguishable from those for ordinary proto-neutron stars in
successful core-collapse supernovae. We discuss that a future detection of
neutrinos from black-hole-forming collapse will contribute to reveal the black
hole formation and to constrain the EOS at high density and temperature.Comment: 32 pages, 33 figures, accepted for publication in Ap

### R-Process Nucleosynthesis In Neutrino-Driven Winds From A Typical Neutron Star With M = 1.4 Msun

We study the effects of the outer boundary conditions in neutrino-driven
winds on the r-process nucleosynthesis. We perform numerical simulations of
hydrodynamics of neutrino-driven winds and nuclear reaction network
calculations of the r-process. As an outer boundary condition of hydrodynamic
calculations, we set a pressure upon the outermost layer of the wind, which is
approaching toward the shock wall. Varying the boundary pressure, we obtain
various asymptotic thermal temperature of expanding material in the
neutrino-driven winds for resulting nucleosynthesis. We find that the
asymptotic temperature slightly lower than those used in the previous studies
of the neutrino-driven winds can lead to a successful r-process abundance
pattern, which is in a reasonable agreement with the solar system r-process
abundance pattern even for the typical proto-neutron star mass Mns ~ 1.4 Msun.
A slightly lower asymptotic temperature reduces the charged particle reaction
rates and the resulting amount of seed elements and lead to a high
neutron-to-seed ratio for successful r-process. This is a new idea which is
different from the previous models of neutrino-driven winds from very massive
(Mns ~ 2.0 Msun) and compact (Rns ~ 10 km) neutron star to get a short
expansion time and a high entropy for a successful r-process abundance pattern.
Although such a large mass is sometimes criticized from observational facts on
a neutron star mass, we dissolve this criticism by reconsidering the boundary
condition of the wind. We also explore the relation between the boundary
condition and neutron star mass, which is related to the progenitor mass, for
successful r-process.Comment: 14 pages, 2 figure

### Monopole Excitation to Cluster States

We discuss strength of monopole excitation of the ground state to cluster
states in light nuclei. We clarify that the monopole excitation to cluster
states is in general strong as to be comparable with the single particle
strength and shares an appreciable portion of the sum rule value in spite of
large difference of the structure between the cluster state and the
shell-model-like ground state. We argue that the essential reasons of the large
strength are twofold. One is the fact that the clustering degree of freedom is
possessed even by simple shell model wave functions. The detailed feature of
this fact is described by the so-called Bayman-Bohr theorem which tells us that
SU(3) shell model wave function is equivalent to cluster model wave function.
The other is the ground state correlation induced by the activation of the
cluster degrees of freedom described by the Bayman-Bohr theorem. We
demonstrate, by deriving analytical expressions of monopole matrix elements,
that the order of magnitude of the monopole strength is governed by the first
reason, while the second reason plays a sufficient role in reproducing the data
up to the factor of magnitude of the monopole strength. Our explanation is made
by analysing three examples which are the monopole excitations to the $0^+_2$
and $0^+_3$ states in $^{16}$O and the one to the $0^+_2$ state in $^{12}$C.
The present results imply that the measurement of strong monopole transitions
or excitations is in general very useful for the study of cluster states.Comment: 11 pages, 1 figure: revised versio

### The Grounds For Time Dependent Market Potentials From Dealers' Dynamics

We apply the potential force estimation method to artificial time series of
market price produced by a deterministic dealer model. We find that dealers'
feedback of linear prediction of market price based on the latest mean price
changes plays the central role in the market's potential force. When markets
are dominated by dealers with positive feedback the resulting potential force
is repulsive, while the effect of negative feedback enhances the attractive
potential force.Comment: 9 pages, 3 figures, proceedings of APFA

### On the Genus Expansion in the Topological String Theory

A systematic formulation of the higher genus expansion in topological string
theory is considered. We also develop a simple way of evaluating genus zero
correlation functions. At higher genera we derive some interesting formulas for
the free energy in the $A_1$ and $A_2$ models. We present some evidence that
topological minimal models associated with Lie algebras other than the A-D-E
type do not have a consistent higher genus expansion beyond genus one. We also
present some new results on the $CP^1$ model at higher genera.Comment: 36 pages, phyzzx, UTHEP-27

### Large magnetic field-induced spectral weight enhancement of high-energy spin excitations in $La_{1.88}Sr_{0.12}CuO_{4}$

We report electronic Raman scattering experiments on a superconducting ${\rm
La_{1.88}Sr_{0.12}CuO_{4}}$ single crystal in a magnetic field. At low
temperatures, the spectral weight of the high-energy two-magnon peak increases
linearly with field and is amplified by a factor of more than two at 14 T. The
effect disappears at elevated temperatures and is not present in undoped ${\rm
La_{2}CuO_{4}}$. This observation is discussed in terms of an electronically
inhomogeneous state in which the field enhances the volume fraction of a phase
with local antiferromagnetic order at the expense of the superconducting phase.Comment: to appear in PR

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