24,741 research outputs found

### Stationary quantum Markov process for the Wigner function

As a stochastic model for quantum mechanics we present a stationary quantum
Markov process for the time evolution of the Wigner function on a lattice phase
space Z_N x Z_N with N odd. By introducing a phase factor extension to the
phase space, each particle can be treated independently. This is an improvement
on earlier methods that require the whole distribution function to determine
the evolution of a constituent particle. The process has branching and
vanishing points, though a finite time interval can be maintained between the
branchings. The procedure to perform a simulation using the process is
presented.Comment: 12 pages, no figures; replaced with version accepted for publication
in J. Phys. A, title changed, an example adde

### Initial Shock Waves for Explosive Nucleosynthesis in Type II Supernova

We have performed 1-dimensional calculations for explosive nucleosynthesis in
collapse-driven supernova and investigated its sensitivity to the initial form
of the shock wave. We have found the tendency that the peak temperature becomes
higher around the mass cut if the input energy is injected more in the form of
kinetic energy rather than internal energy. Then, the mass cut becomes larger,
and, as a result, neutron-rich matter is less included in the ejecta; this is
favorable for producing the observational data compared with a previous model.
Our results imply that the standard method to treat various processes for
stellar evolution, such as convection and electron capture during the silicon
burning stage, are still compatible with the calculation of explosive
nucleosynthesis.Comment: 20 pages, 6 figures, LaTe

### Explosive Nucleosynthesis in Axisymmetrically Deformed Type II Supernovae

Explosive nucleosynthesis under the axisymmetric explosion in Type II
supernova has been performed by means of two dimensional hydrodynamical
calculations. We have compared the results with the observations of SN 1987A.
Our chief findings are as follows: (1) $^{44}Ti$ is synthesized so much as to
explain the tail of the bolometric light curve of SN 1987A. We think this is
because the alpha-rich freezeout takes place more actively under the
axisymmetric explosion. (2) $^{57}Ni$ and $^{58}Ni$ tend to be overproduced
compared with the observations. However, this tendency relies strongly on the
progenitor's model.
We have also compared the abundance of each element in the mass number range
$A= 16-73$ with the solar values. We have found three outstanding features. (1)
For the nuclei in the range $A=16-40$, their abundances are insensitive to the
initial form of the shock wave. This insensitivity is favored since the
spherical calculations thus far can explain the solar system abundances in this
mass range. (2) There is an enhancement around A=45 in the axisymmetric
explosion compared with the spherical explosion fairly well. In particular,
$^{44}Ca$, which is underproduced in the present spherical calculations, is
enhanced significantly. (3) In addition, there is an enhancement around A=65.
This tendency does not rely on the form of the mass cut but of the initial
shock wave. This enhancement may be the problem of the overproduction in this
mass range, although this effect would be relatively small since Type I
supernovae are chiefly responsible for this mass number range.Comment: 32 pages, 12 figures, LaTe

### Analysis of (K^-,K^+) inclusive spectrum with semiclassical distorted wave model

The inclusive K^+ momentum spectrum in the 12C(K^-,K^+) reaction is
calculated by the semiclassical distorted wave (SCDW) model, including the
transition to the \Xi^- bound state. The calculated spectra with the strength
of the \Xi^--nucleus potential -50, -20, and +10 MeV are compared with the
experimental data measured at KEK with p_{K^-}=1.65 GeV/c. The shape of the
spectrum is reproduced by the calculation. Though the inclusive spectrum
changes systematically depending on the potential strength, it is not possible
to obtain a constraint on the potential from the present data. The calculated
spectrum is found to have strong emission-angle dependence. We also investigate
the incident K^- momentum dependence of the spectrum to see the effect of the
Fermi motion of the target nucleons which is explicitly treated in the SCDW
method.Comment: 7 pages, 5 figure

### Unitary-process discrimination with error margin

We investigate a discrimination scheme between unitary processes. By
introducing a margin for the probability of erroneous guess, this scheme
interpolates the two standard discrimination schemes: minimum-error and
unambiguous discrimination. We present solutions for two cases. One is the case
of two unitary processes with general prior probabilities. The other is the
case with a group symmetry: the processes comprise a projective representation
of a finite group. In the latter case, we found that unambiguous discrimination
is a kind of "all or nothing": the maximum success probability is either 0 or
1. We also closely analyze how entanglement with an auxiliary system improves
discrimination performance.Comment: 9 pages, 3 figures, presentation improved, typos corrected, final
versio

### Optimal estimation of a physical observable's expectation value for pure states

We study the optimal way to estimate the quantum expectation value of a
physical observable when a finite number of copies of a quantum pure state are
presented. The optimal estimation is determined by minimizing the squared error
averaged over all pure states distributed in a unitary invariant way. We find
that the optimal estimation is "biased", though the optimal measurement is
given by successive projective measurements of the observable. The optimal
estimate is not the sample average of observed data, but the arithmetic average
of observed and "default nonobserved" data, with the latter consisting of all
eigenvalues of the observable.Comment: v2: 5pages, typos corrected, journal versio

- …