9,926 research outputs found
Spectrum of the Hermitian Wilson-Dirac Operator for a Uniform Magnetic Field in Two Dimensions
It is shown that the eigenvalue problem for the hermitian Wilson-Dirac
operator of for a uniform magnetic field in two dimensions can be reduced to
one-dimensional problem described by a relativistic analog of the Harper
equation. An explicit formula for the secular equations is given in term of a
set of polynomials. The spectrum exhibits a fractal structure in the infinite
volume limit. An exact result concerning the index theorem for the overlap
Dirac operator is obtained.Comment: 8 pages, latex, 3 eps figures, minor correction
The Role of Expectation in Job Search and Firm Size Effect on Wages
One of the most puzzling facts in economics is the firm size-wage effect. After controlling for the observable characteristics of workers (age, gender, education, residence etc.), firms (industry, occupation, work conditions etc.) and negotiation effect (unionization), one still finds that the sheer size of a firm increases the wage, contrary to the one-good one-price doctrine. We provide a simple dynamic game model of wage determination to give a new rationale to the firm size-wage effect. We think that the wages are not market clearing prices but strategies by firms. Firms choose wages to control workers' search behavior. The essential feature of the model is that a large firm's history of wages is observable to all the current and future workers, while a small firm is not visible and only its current offer is observable. Therefore a small firm is expected to be a myopic low-wage payer, and its workers search and quit often. A large firm can prevent search if it maintained a high wage throughout the past, thus making workers expect high future wages. In this way, the firm size determines the worker expectations of its future wages, which changes the quit rate and equilibrium wages. To give additional support to our theoretical result, we test a new aspect of firm size-wage effect. Since the effect on wage levels are extensively studied, we derive two main hypotheses on wage gains after job changes. (H1) The proportion of firms that are larger than the previous employer increases the wage gain. (H2) The size of the previous employer decreases the wage gain. The firm size distribution effect (H1) is a new test. We obtain supports for both. Thus we conclude that the wages are strategies and affected by how workers utilize the firm size information in changing jobs. (297 words.)
Triton binding energy calculated from the SU_6 quark-model nucleon-nucleon interaction
Properties of the three-nucleon bound state are examined in the Faddeev
formalism, in which the quark-model nucleon-nucleon interaction is explicitly
incorporated to calculate the off-shell T-matrix. The most recent version,
fss2, of the Kyoto-Niigata quark-model potential yields the ground-state energy
^3H=-8.514 MeV in the 34 channel calculation, when the np interaction is used
for the nucleon-nucleon interaction. The charge root mean square radii of the
^3H and ^3He are 1.72 fm and 1.90 fm, respectively, including the finite size
correction of the nucleons. These values are the closest to the experiments
among many results obtained by detailed Faddeev calculations employing modern
realistic nucleon-nucleon interaction models.Comment: 10 pages, no figure
Equivalent hyperon-nucleon interactions in low-momentum space
Equivalent interactions in a low-momentum space for the , and interactions are calculated, using the SU quark model
potential as well as the Nijmegen OBEP model as the input bare interaction.
Because the two-body scattering data has not been accumulated sufficiently to
determine the hyperon-nucleon interactions unambiguously, the construction of
the potential even in low-energy regions has to rely on a theoretical model.
The equivalent interaction after removing high-momentum components is still
model dependent. Because this model dependence reflects the character of the
underlying potential model, it is instructive for better understanding of
baryon-baryon interactions in the strangeness sector to study the low-momentum
space interactions.Comment: 9 pages, 13 figures, accepted for publication in Phys. Rev.
Addendum: Triton and hypertriton binding energies calculated from SU_6 quark-model baryon-baryon interactions
Previously we calculated the binding energies of the triton and hypertriton,
using an SU_6 quark-model interaction derived from a resonating-group method of
two baryon clusters. In contrast to the previous calculations employing the
energy-dependent interaction kernel, we present new results using a
renormalized interaction, which is now energy independent and reserves all the
two-baryon data. The new binding energies are slightly smaller than the
previous values. In particular the triton binding energy turns out to be 8.14
MeV with a charge-dependence correction of the two-nucleon force, 190 keV,
being included. This indicates that about 350 keV is left for the energy which
is to be accounted for by three-body forces.Comment: 4 pages, 1 figur
A Realistic Description of Nucleon-Nucleon and Hyperon-Nucleon Interactions in the SU_6 Quark Model
We upgrade a SU_6 quark-model description for the nucleon-nucleon and
hyperon-nucleon interactions by improving the effective meson-exchange
potentials acting between quarks. For the scalar- and vector-meson exchanges,
the momentum-dependent higher-order term is incorporated to reduce the
attractive effect of the central interaction at higher energies. The
single-particle potentials of the nucleon and Lambda, predicted by the G-matrix
calculation, now have proper repulsive behavior in the momentum region q_1=5 -
20 fm^-1. A moderate contribution of the spin-orbit interaction from the
scalar-meson exchange is also included. As to the vector mesons, a dominant
contribution is the quadratic spin-orbit force generated from the rho-meson
exchange. The nucleon-nucleon phase shifts at the non-relativistic energies up
to T_lab=350 MeV are greatly improved especially for the 3E states. The
low-energy observables of the nucleon-nucleon and the hyperon-nucleon
interactions are also reexamined. The isospin symmetry breaking and the Coulomb
effect are properly incorporated in the particle basis. The essential feature
of the Lambda N - Sigma N coupling is qualitatively similar to that obtained
from the previous models. The nuclear saturation properties and the
single-particle potentials of the nucleon, Lambda and Sigma are reexamined
through the G-matrix calculation. The single-particle potential of the Sigma
hyperon is weakly repulsive in symmetric nuclear matter. The single-particle
spin-orbit strength for the Lambda particle is very small, in comparison with
that of the nucleons, due to the strong antisymmetric spin-orbit force
generated from the Fermi-Breit interaction.Comment: Revtex v2.09, 69 pages with 25 figure
Comparison between the Cramer-Rao and the mini-max approaches in quantum channel estimation
In a unified viewpoint in quantum channel estimation, we compare the
Cramer-Rao and the mini-max approaches, which gives the Bayesian bound in the
group covariant model. For this purpose, we introduce the local asymptotic
mini-max bound, whose maximum is shown to be equal to the asymptotic limit of
the mini-max bound. It is shown that the local asymptotic mini-max bound is
strictly larger than the Cramer-Rao bound in the phase estimation case while
the both bounds coincide when the minimum mean square error decreases with the
order O(1/n). We also derive a sufficient condition for that the minimum mean
square error decreases with the order O(1/n).Comment: In this revision, some unlcear parts are clarifie
Quantum Stability of (2+1)-Spacetimes with Non-Trivial Topology
Quantum fields are investigated in the (2+1)-open-universes with non-trivial
topologies by the method of images. The universes are locally de Sitter
spacetime and anti-de Sitter spacetime. In the present article we study
spacetimes whose spatial topologies are a torus with a cusp and a sphere with
three cusps as a step toward the more general case. A quantum energy momentum
tensor is obtained by the point stripping method. Though the cusps are no
singularities, the latter cusps cause the divergence of the quantum field. This
suggests that only the latter cusps are quantum mechanically unstable. Of
course at the singularity of the background spacetime the quantum field
diverges. Also the possibility of the divergence of topological effect by a
negative spatial curvature is discussed. Since the volume of the negatively
curved space is larger than that of the flat space, one see so many images of a
single source by the non-trivial topology. It is confirmed that this divergence
does not appear in our models of topologies. The results will be applicable to
the case of three dimensional multi black hole\cite{BR}.Comment: 17 pages, revtex, 3 uuencoded figures containe
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