45,077 research outputs found
Foundations of self-consistent particle-rotor models and of self-consistent cranking models
The Kerman-Klein formulation of the equations of motion for a nuclear shell
model and its associated variational principle are reviewed briefly. It is then
applied to the derivation of the self-consistent particle-rotor model and of
the self-consistent cranking model, for both axially symmetric and triaxial
nuclei. Two derivations of the particle-rotor model are given. One of these is
of a form that lends itself to an expansion of the result in powers of the
ratio of single-particle angular momentum to collective angular momentum, that
is essentual to reach the cranking limit. The derivation also requires a
distinct, angular-momentum violating, step. The structure of the result implies
the possibility of tilted-axis cranking for the axial case and full
three-dimensional cranking for the triaxial one. The final equations remain
number conserving. In an appendix, the Kerman-Klein method is developed in more
detail, and the outlines of several algorithms for obtaining solutions of the
associated non-linear formalism are suggested.Comment: 29 page
Single Boson Images Via an Extended Holstein Primakoff Mapping
The Holstein-Primakoff mapping for pairs of bosons is extended in order to
accommodate single boson mapping. The proposed extension allows a variety of
applications and especially puts the formalism at finite temperature on firm
grounds. The new mapping is applied to the O(N+1) anharmonic oscillator with
global symmetry broken down to O(N). It is explicitly demonstrated that
N-Goldstone modes appear. This result generalizes the Holstein-Primakoff
mapping for interacting boson as developed in ref.[1].Comment: 9 pages, LaTeX. Physical content unchanged. Unnecessary figure
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Classical mappings of the symplectic model and their application to the theory of large-amplitude collective motion
We study the algebra Sp(n,R) of the symplectic model, in particular for the
cases n=1,2,3, in a new way. Starting from the Poisson-bracket realization we
derive a set of partial differential equations for the generators as functions
of classical canonical variables. We obtain a solution to these equations that
represents the classical limit of a boson mapping of the algebra. The
relationship to the collective dynamics is formulated as a theorem that
associates the mapping with an exact solution of the time-dependent Hartree
approximation. This solution determines a decoupled classical symplectic
manifold, thus satisfying the criteria that define an exactly solvable model in
the theory of large amplitude collective motion. The models thus obtained also
provide a test of methods for constructing an approximately decoupled manifold
in fully realistic cases. We show that an algorithm developed in one of our
earlier works reproduces the main results of the theorem.Comment: 23 pages, LaTeX using REVTeX 3.
Persistence of characteristics of an ordered flux line lattice above the second peak in
We report Small Angle Neutron Scattering measurements of the flux lines
lattice (FLL) in . As previously reported, the
scattered intensity decreases strongly when the magnetic field is increased,
but it remains measurable far above the second peak. The direct observation of
Bragg peaks proves that the characteristics of a lattice are still present. No
structural features related to a symmetry breaking, such as a liquid like or an
amorphous state, can be observed. However, the associated scattered intensity
is very low and is difficult to explain. We discuss the coexistence between two
FLL states as a possible interpretation.Comment: accepted for publication in Phys Rev
On Dimensional Degression in AdS(d)
We analyze the pattern of fields in d+1 dimensional anti-de Sitter space in
terms of those in d dimensional anti-de Sitter space. The procedure, which is
neither dimensional reduction nor dimensional compactification, is called
dimensional degression. The analysis is performed group-theoretically for all
totally symmetric bosonic and fermionic representations of the anti-de Sitter
algebra. The field-theoretical analysis is done for a massive scalar field in
AdS(d+d) and massless spin one-half, spin one, and spin two fields in
AdS(d+1). The mass spectra of the resulting towers of fields in AdS(d) are
found. For the scalar field case, the obtained results extend to the shadow
sector those obtained by Metsaev in [1] by a different method.Comment: 30 page
Upper critical field in {BaKBiO}: magnetotransport versus magnetotunneling
Elastic tunneling is used as a powerful direct tool to determine the upper
critical field in the high- oxide BaKBiO. The
temperature dependence of inferred from the tunneling follows the
Werthamer-Helfand-Hohenberg prediction for type-II superconductors. A
comparison will be made with resistively determined critical field data.Comment: 4 pages incl. 5 figure
Sub-Alfvenic Non-Ideal MHD Turbulence Simulations with Ambipolar Diffusion: I. Turbulence Statistics
Most numerical investigations on the role of magnetic fields in turbulent
molecular clouds (MCs) are based on ideal magneto-hydrodynamics (MHD). However,
MCs are weakly ionized, so that the time scale required for the magnetic field
to diffuse through the neutral component of the plasma by ambipolar diffusion
(AD) can be comparable to the dynamical time scale. We have performed a series
of 256^3 and 512^3 simulations on supersonic but sub-Alfvenic turbulent systems
with AD using the Heavy-Ion Approximation developed in Li, McKee, & Klein
(2006). Our calculations are based on the assumption that the number of ions is
conserved, but we show that these results approximately apply to the case of
time-dependent ionization in molecular clouds as well. Convergence studies
allow us to determine the optimal value of the ionization mass fraction when
using the heavy-ion approximation for low Mach number, sub-Alfvenic turbulent
systems. We find that ambipolar diffusion steepens the velocity and magnetic
power spectra compared to the ideal MHD case. Changes in the density PDF, total
magnetic energy, and ionization fraction are determined as a function of the AD
Reynolds number. The power spectra for the neutral gas properties of a strongly
magnetized medium with a low AD Reynolds number are similar to those for a
weakly magnetized medium; in particular, the power spectrum of the neutral
velocity is close to that for Burgers turbulence.Comment: 37 pages, 11 figures, 4 table
Symmetry dependence of phonon lineshapes in superconductors with anisotropic gaps
The temperature dependence below of the lineshape of optical phonons
of different symmetry as seen in Raman scattering is investigated for
superconductors with anisotropic energy gaps. It is shown that the symmetry of
the electron-phonon vertex produces non-trivial couplings to an anisotropic
energy gap which leads to unique changes in the phonon lineshape for phonons of
different symmetry. The phonon lineshape is calculated in detail for
and phonons in a superconductor with pairing
symmetry. The role of satellite peaks generated by the electron-phonon coupling
are also addressed. The theory accounts for the substantial phonon narrowing of
the phonon, while narrowing of the phonon which is
indistinguishable from the normal state is shown, in agreement with recent
measurements on BSCCO.Comment: 15 pages (3 Figures available upon request), Revtex, 1
Nanometer Scale Mapping of the Density of States in an Inhomogeneous Superconductor
Using high speed scanning tunneling spectroscopy, we perform a full mapping
of the quasiparticle density of states (DOS) in single crystals of
BiPbSrCaCuO(2212). The measurements carried out at 5 K showed a complex spatial
pattern of important variations of the local DOS on the nanometer scale.
Superconducting areas are co-existing with regions of a smooth and larger
gap-like DOS structure. The superconducting regions are found to have a minimum
size of about 3 nm. The role of Pb-introduced substitutional disorder in the
observed spatial variations of the local DOS is discussed.Comment: 4 page Letter with 3 figures (2 color figures
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