1,026 research outputs found
Hartree-Fock and Many-Body Perturbation Theory with Correlated Realistic NN-Interactions
We employ correlated realistic nucleon-nucleon interactions for the
description of nuclear ground states throughout the nuclear chart within the
Hartree-Fock approximation. The crucial short-range central and tensor
correlations, which are induced by the realistic interaction and cannot be
described by the Hartree-Fock many-body state itself, are included explicitly
by a state-independent unitary transformation in the framework of the unitary
correlation operator method (UCOM). Using the correlated realistic interaction
V_UCOM resulting from the Argonne V18 potential, bound nuclei are obtained
already on the Hartree-Fock level. However, the binding energies are smaller
than the experimental values because long-range correlations have not been
accounted for. Their inclusion by means of many-body perturbation theory leads
to a remarkable agreement with experimental binding energies over the whole
mass range from He-4 to Pb-208, even far off the valley of stability. The
observed perturbative character of the residual long-range correlations and the
apparently small net effect of three-body forces provides promising
perspectives for a unified nuclear structure description.Comment: 14 pages, 8 figures, 3 tables, using REVTEX
Spectrum of the Schr\"odinger operator in a perturbed periodically twisted tube
We study Dirichlet Laplacian in a screw-shaped region, i.e. a straight
twisted tube of a non-circular cross section. It is shown that a local
perturbation which consists of "slowing down" the twisting in the mean gives
rise to a non-empty discrete spectrum.Comment: LaTeX2e, 10 page
Properties of Nambu-Goldstone Bosons in a Single-Component Bose-Einstein Condensate
We theoretically study the properties of Nambu-Goldstone bosons in an
interacting single-component Bose-Einstein condensate (BEC). We first point out
that the proofs of Goldstone's theorem by Goldstone, et al. [Phys. Rev. {\bf
127} (1962) 965] may be relevant to distinct massless modes of the BEC: whereas
the first proof deals with the poles of the single-particle Green's function
, the second one concerns those of the two-particle Green's function.
Thus, there may be multiple Nambu-Goldstone bosons even in the single-component
BEC with broken U(1) symmetry. The second mode turns out to have an infinite
lifetime in the long-wavelength limit in agreement with the conventional
viewpoint. In contrast, the first mode from , i.e., the Bogoliubov
mode in the weak-coupling regime, is shown to be a "bubbling" mode fluctuating
temporally out of and back into the condensate. The substantial lifetime
originates from an "improper" structure of the self-energy inherent in the BEC,
which has been overlooked so far and will be elucidated here, and removes
various infrared divergences pointed out previously.Comment: 9 pages, 6 gigure
Polymers in Curved Boxes
We apply results derived in other contexts for the spectrum of the Laplace
operator in curved geometries to the study of an ideal polymer chain confined
to a spherical annulus in arbitrary space dimension D and conclude that the
free energy compared to its value for an uncurved box of the same thickness and
volume, is lower when , stays the same when , and is higher when
\mbox{}. Thus confining an ideal polymer chain to a cylindrical shell,
lowers the effective bending elasticity of the walls, and might induce
spontaneous symmetry breaking, i.e. bending. (Actually, the above mentioned
results show that {\em {any}} shell in induces this effect, except for
a spherical shell). We compute the contribution of this effect to the bending
rigidities in the Helfrich free energy expression.Comment: 20 pages RevTeX, epsf; 4 figures; submitted to Macromoledule
A Hardy inequality in twisted waveguides
We show that twisting of an infinite straight three-dimensional tube with
non-circular cross-section gives rise to a Hardy-type inequality for the
associated Dirichlet Laplacian. As an application we prove certain stability of
the spectrum of the Dirichlet Laplacian in locally and mildly bent tubes.
Namely, it is known that any local bending, no matter how small, generates
eigenvalues below the essential spectrum of the Laplacian in the tubes with
arbitrary cross-sections rotated along a reference curve in an appropriate way.
In the present paper we show that for any other rotation some critical strength
of the bending is needed in order to induce a non-empty discrete spectrum.Comment: LaTeX, 20 page
Effects of Monovalent and Divalent Cations on Ca2+ Fluxes Across Chromaffin Secretory Membrane Vesicles
Abstract: Bovine chromaffin secretory vesicle ghosts loaded with Na+ were found to take up Ca2+ when incubated in K+ media or in sucrose media containing micromolar concentrations of free Ca2+. Li+- or choline+loaded ghosts did not take up Ca2+. The Ca2+ accumulated by Na+-loaded ghosts could be released by the Ca2+ ionophore A23187, but not by EGTA. Ca2+ uptake was inhibited by external Sr2+, Na +, Li +, or choline +. All the 45Ca2+ accumulated by Na+-dependent Ca2+ uptake could be released by external Na +, indicating that both Ca2+ influx and efflux occur in a Na+-dependent manner. Na + -dependent Ca2+ uptake and release were only slightly inhibited by Mg2+. In the presence of the Na+ ionophore Monensin the Ca2+ uptake by Na +-loaded ghosts was reduced. Ca2+ sequestered by the Na+-dependent mechanism could also be released by external Ca2+ or Sr2+ but not by Mg2+, indicating the presence of a Ca2+/Ca2+ exchange activity in secretory membrane vesicles. This Ca2+/Ca2+ exchange system is inhibited by Mg2+, but not by Sr2+. The Na + -dependent Ca2+ uptake system in the presence of Mg2+ is a saturable process with an apparent Km of 0.28 μM and a Vmax= 14.5 nmol min−1 mg protein−1. Ruthenium red inhibited neither the Na+/Ca2+ nor the Ca2+/Ca2+ exchange, even at high concentrations
Neutrino Masses and the Gluino Axion Model
We extend the recently proposed gluino axion model to include neutrino
masses. We discuss how the canonical seesaw model and the Higgs triplet model
may be realized in this framework. In the former case, the heavy singlet
neutrinos are contained in superfields which do not have any vacuum expectation
value, whereas the gluino axion is contained in one which does. We also
construct a specific renormalizable model which realizes the mass scale
relationship , where is the axion decay constant
and is a large effective mass parameter.Comment: 8 pages, no figur
Once again on electromagnetic properties of a domain wall interacting with charged fermions
The response to a magnetic flux is considered of the vacuum state of charged
Dirac fermions interacting with a domain wall made of a neutral spinless field
in (3+1) dimensions with the fermion mass having a phase variation across the
wall. It is pointed out that due to simple C parity arguments the spontaneous
magnetization for this system is necessarily zero, thus invalidating some
claims to the contrary in the literature. The cancellation of the spontaneous
magnetization is explicitly demonstrated in a particular class of models. The
same calculation produces a general formula for the electric charge density
induced by the magnetic flux -- an effect previously discussed in the
literature for axionic domain walls. The distribution of the induced charge is
calculated in specific models.Comment: 15 page
A Gapless Theory of Bose-Einstein Condensation in Dilute Gases at Finite Temperature
In this paper we develop a gapless theory of BEC which can be applied to both
trapped and homogeneous gases at zero and finite temperature. The many-body
Hamiltonian for the system is written in a form which is approximately
quadratic with higher order cubic and quartic terms. The quadratic part is
diagonalized exactly by transforming to a quasiparticle basis, while the
non-quadratic terms are dealt with using first and second order perturbation
theory. The conventional treatment of these terms, based on factorization
approximations, is shown to be inconsistent.
Infra-red divergences can appear in individual terms of the perturbation
expansion, but we show analytically that the total contribution beyond
quadratic order is finite. The resulting excitation spectrum is gapless and the
energy shifts are small for a dilute gas away from the critical region,
justifying the use of perturbation theory. Ultra-violet divergences can appear
if a contact potential is used to describe particle interactions. We show that
the use of this potential as an approximation to the two-body T-matrix leads
naturally to a high-energy renormalization.
The theory developed in this paper is therefore well-defined at both low and
high energy and provides a systematic description of Bose-Einstein condensation
in dilute gases. It can therefore be used to calculate the energies and decay
rates of the excitations of the system at temperatures approaching the phase
transition.Comment: 39 pages of Revtex. 1 figur
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