42,871 research outputs found
A Novel Method for the Solution of the Schroedinger Eq. in the Presence of Exchange Terms
In the Hartree-Fock approximation the Pauli exclusion principle leads to a
Schroedinger Eq. of an integro-differential form. We describe a new spectral
noniterative method (S-IEM), previously developed for solving the
Lippman-Schwinger integral equation with local potentials, which has now been
extended so as to include the exchange nonlocality. We apply it to the
restricted case of electron-Hydrogen scattering in which the bound electron
remains in the ground state and the incident electron has zero angular
momentum, and we compare the acuracy and economy of the new method to three
other methods. One is a non-iterative solution (NIEM) of the integral equation
as described by Sams and Kouri in 1969. Another is an iterative method
introduced by Kim and Udagawa in 1990 for nuclear physics applications, which
makes an expansion of the solution into an especially favorable basis obtained
by a method of moments. The third one is based on the Singular Value
Decomposition of the exchange term followed by iterations over the remainder.
The S-IEM method turns out to be more accurate by many orders of magnitude than
any of the other three methods described above for the same number of mesh
points.Comment: 29 pages, 4 figures, submitted to Phys. Rev.
Interference through quantum dots
We discuss the effect of quantum interference on transport through a quantum
dot system. We introduce an indirect coherent coupling parameter alpha, which
provides constructive/destructive interference in the transport current
depending on its phase and the magnetic flux. We estimate the current through
the quantum dot system using the non-equilibrium Green's function method as
well as the master equation method in the sequential tunneling regime. The
visibility of the Aharonov-Bohm oscillation is evaluated. For a large inter-dot
Coulomb interaction, the current is strongly suppressed by the quantum
interference effect, while the current is restored by applying an oscillating
resonance field with the frequency of twice the inter-dot tunneling energy.Comment: 10 pages, 3 figure
Triple sign reversal of Hall effect in HgBa_{2}CaCu_{2}O_{6} thin films after heavy-ion irradiations
Triple sign reversal in the mixed-state Hall effect has been observed for the
first time in ion-irradiated HgBa_{2}CaCu_{2}O_{6} thin films. The negative dip
at the third sign reversal is more pronounced for higher fields, which is
opposite to the case of the first sign reversal near T_c in most high-T_c
superconductors. These observations can be explained by a recent prediction in
which the third sign reversal is attributed to the energy derivative of the
density of states and to a temperature-dependent function related to the
superconducting energy gap. These contributions prominently appear in cases
where the mean free path is significantly decreased, such as our case of
ion-irradiated thin films.Comment: 4 pages, 3 eps figures, submitted Phys. Rev. Let
Neutrino masses along with fermion mass hierarchy
Recently a new mechanism has been proposed to cure the problem of fermion
mass hierarchy in the Standard Model (SM) model. In this scenario, all SM
charged fermions other than top quark arise from higher dimensional operators
involving the SM Higgs field. This model also predicted some interesting
phenomenology of the Higgs boson. We generalize this model to accommodate
neutrino masses (Dirac & Majorana) and also obtain the mixing pattern in the
leptonic sector. To generate neutrino masses, we add extra three right handed
neutrinos in this model.Comment: 20 pages, the content on results and phenomenology have been
expanded, a new section on UV completion of the model has been added and also
some new references, this version has been accepted by Physical Review
Inelastic neutron scattering studies of Crystal Field Levels in PrOsAs
We use neutron scattering to study the Pr crystalline electric field
(CEF) excitations in the filled skutterudite PrOsAs. By comparing
the observed levels and their strengths under neutron excitation with the
theoretical spectrum and neutron excitation intensities, we identify the
Pr CEF levels, and show that the ground state is a magnetic
triplet, and the excited states ,
and are at 0.4, 13 and 23 meV, respectively. A comparison of the
observed CEF levels in PrOsAs with the heavy fermion superconductor
PrOsSb reveals the microscopic origin of the differences in the
ground states of these two filled skutterudites.Comment: 7 pages, 7 figure
Efficiency of Nonlinear Particle Acceleration at Cosmic Structure Shocks
We have calculated the evolution of cosmic ray (CR) modified astrophysical
shocks for a wide range of shock Mach numbers and shock speeds through
numerical simulations of diffusive shock acceleration (DSA) in 1D quasi-
parallel plane shocks. The simulations include thermal leakage injection of
seed CRs, as well as pre-existing, upstream CR populations. Bohm-like diffusion
is assumed. We model shocks similar to those expected around cosmic structure
pancakes as well as other accretion shocks driven by flows with upstream gas
temperatures in the range K and shock Mach numbers spanning
. We show that CR modified shocks evolve to time-asymptotic states
by the time injected particles are accelerated to moderately relativistic
energies (p/mc \gsim 1), and that two shocks with the same Mach number, but
with different shock speeds, evolve qualitatively similarly when the results
are presented in terms of a characteristic diffusion length and diffusion time.
For these models the time asymptotic value for the CR acceleration efficiency
is controlled mainly by shock Mach number. The modeled high Mach number shocks
all evolve towards efficiencies %, regardless of the upstream CR
pressure. On the other hand, the upstream CR pressure increases the overall CR
energy in moderate strength shocks (). (abridged)Comment: 23 pages, 12 ps figures, accepted for Astrophysical Journal (Feb. 10,
2005
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