32,959 research outputs found
On the momentum-dependence of -nuclear potentials
The momentum dependent -nucleus optical potentials are obtained based
on the relativistic mean-field theory. By considering the quarks coordinates of
meson, we introduced a momentum-dependent "form factor" to modify the
coupling vertexes. The parameters in the form factors are determined by fitting
the experimental -nucleus scattering data. It is found that the real
part of the optical potentials decrease with increasing momenta, however
the imaginary potentials increase at first with increasing momenta up to
MeV and then decrease. By comparing the calculated mean
free paths with those from / scattering data, we suggested that the
real potential depth is MeV, and the imaginary potential parameter
is MeV.Comment: 9 pages, 4 figure
Iron-based layered superconductor LaOFFeAs: an antiferromagnetic semimetal
We have studied the newly found superconductor compound LaOFFeAs
through the first-principles density functional theory calculations. We find
that the parent compound LaOFeAs is a quasi-2-dimensional antiferromgnetic
semimetal with most carriers being electrons and with a magnetic moment of
located around each Fe atom on the Fe-Fe square lattice. Furthermore
this is a commensurate antiferromagnetic spin density wave due to the Fermi
surface nesting, which is robust against the F-doping. The observed
superconduction happens on the Fe-Fe antiferromagnetic layer, suggesting a new
superconductivity mechanism, mediated by the spin fluctuations. An abrupt
change on the Hall measurement is further predicted for the parent compound
LaOFeAs.Comment: 4 pages, 7 figure
Exploration of Resonant Continuum and Giant Resonance in the Relativistic Approach
Single-particle resonant-states in the continuum are determined by solving
scattering states of the Dirac equation with proper asymptotic conditions in
the relativistic mean field theory (RMF). The regular and irregular solutions
of the Dirac equation at a large radius where the nuclear potentials vanish are
relativistic Coulomb wave functions, which are calculated numerically.
Energies, widths and wave functions of single-particle resonance states in the
continuum for ^{120}Sn are studied in the RMF with the parameter set of NL3.
The isoscalar giant octupole resonance of ^{120}Sn is investigated in a fully
consistent relativistic random phase approximation. Comparing the results with
including full continuum states and only those single-particle resonances we
find that the contributions from those resonant-states dominate in the nuclear
giant resonant processes.Comment: 16 pages, 2 figure
Exact solution of the two-axis countertwisting Hamiltonian for the half-integer case
Bethe ansatz solutions of the two-axis countertwisting Hamiltonian for any
(integer and half-integer) are derived based on the Jordan-Schwinger
(differential) boson realization of the algebra after desired Euler
rotations, where is the total angular momentum quantum number of the
system. It is shown that solutions to the Bethe ansatz equations can be
obtained as zeros of the extended Heine-Stieltjes polynomials. Two sets of
solutions, with solution number being and respectively when is an
integer and each when is a half-integer, are obtained. Properties
of the zeros of the related extended Heine-Stieltjes polynomials for
half-integer cases are discussed. It is clearly shown that double
degenerate level energies for half-integer are symmetric with respect to
the axis. It is also shown that the excitation energies of the `yrast'
and other `yrare' bands can all be asymptotically given by quadratic functions
of , especially when is large.Comment: LaTex 12 pages, 3 figures. Major cosmetic type revision. arXiv admin
note: text overlap with arXiv:1609.0558
The reaction at low energies in a chiral quark model
A chiral quark-model approach is extended to the study of the
scattering at low energies. The process of at
MeV/c (i.e. the center mass energy GeV) is
investigated. This approach is successful in describing the differential cross
sections and total cross section with the roles of the low-lying
resonances in shells clarified. The dominates the
reactions over the energy region considered here. Around MeV/c,
the is responsible for a strong resonant peak in the
cross section. The has obvious contributions around
MeV/c, while the contribution of is less
important in this energy region. The non-resonant background contributions,
i.e. -channel and -channel, also play important roles in the explanation
of the angular distributions due to amplitude interferences.Comment: 18 pages and 7 figure
Exact solution of the two-axis countertwisting Hamiltonian
It is shown that the two-axis countertwisting Hamiltonian is exactly solvable
when the quantum number of the total angular momentum of the system is an
integer after the Jordan-Schwinger (differential) boson realization of the
SU(2) algebra. Algebraic Bethe ansatz is used to get the exact solution with
the help of the SU(1,1) algebraic structure, from which a set of Bethe ansatz
equations of the problem is derived. It is shown that solutions of the Bethe
ansatz equations can be obtained as zeros of the Heine-Stieltjes polynomials.
The total number of the four sets of the zeros equals exactly to for a
given integer angular momentum quantum number , which proves the
completeness of the solutions. It is also shown that double degeneracy in level
energies may also occur in the limit for integer case
except a unique non-degenerate level with zero excitation energy.Comment: LaTex 10 pages. Version to appear in Annals of Physic
Aperiodic Quantum Random Walks
We generalize the quantum random walk protocol for a particle in a
one-dimensional chain, by using several types of biased quantum coins, arranged
in aperiodic sequences, in a manner that leads to a rich variety of possible
wave function evolutions. Quasiperiodic sequences, following the Fibonacci
prescription, are of particular interest, leading to a sub-ballistic
wavefunction spreading. In contrast, random sequences leads to diffusive
spreading, similar to the classical random walk behaviour. We also describe how
to experimentally implement these aperiodic sequences.Comment: 4 pages and 4 figure
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