19 research outputs found
The Role of Ground State Correlations in the Single-Particle Strength of Odd Nuclei with Pairing
A method based on the consistent use of the Green function formalism has been
developed to calculate the distribution of the single-particle strength in odd
nuclei with pairing. The method takes into account the quasiparticle-phonon
interaction, ground state correlations and a "refinement" of phenomenological
single-particle energies and pairing gap values from the quasiparticle-phonon
interaction under consideration. The calculations for 121Sn and 119Sn that were
performed in the quasiparticlephonon approximation, have shown a
reasonable agreement with experiment. The ground state correlations play a
noticeable role and mostly improve the agreement with experiment or shift the
results to the right direction.Comment: 11 page
Field-linked States of Ultracold Polar Molecules
We explore the character of a novel set of ``field-linked'' states that were
predicted in [A. V. Avdeenkov and J. L. Bohn, Phys. Rev. Lett. 90, 043006
(2003)]. These states exist at ultralow temperatures in the presence of an
electrostatic field, and their properties are strongly dependent on the field's
strength. We clarify the nature of these quasi-bound states by constructing
their wave functions and determining their approximate quantum numbers. As the
properties of field-linked states are strongly defined by anisotropic dipolar
and Stark interactions, we construct adiabatic surfaces as functions of both
the intermolecular distance and the angle that the intermolecular axis makes
with the electric field. Within an adiabatic approximation we solve the 2-D
Schrodinger equation to find bound states, whose energies correlate well with
resonance features found in fully-converged multichannel scattering
calculations
Interaction of the single-particle and collective degrees of freedom in non-magic nuclei: the role of phonon tadpole terms
A method of a consistent consideration of the phonon contributions to mass
and gap operators in non-magic nuclei is developed in the so-called g^2
approximation, where g is the low-lying phonon creation amplitude. It includes
simultaneous accounting for both the usual non-local terms and the phonon
tadpole ones. The relations which allow the tadpoles to be calculated without
any new parameters are derived. As an application of the results, the role of
the phonon tadpoles in the single-particle strength distribution and in the
single-particle energies and gap values has been considered. Relation to the
problem of the surface nature of pairing is discussed.Comment: 22 pages, 7 figure
Molecular vibration in cold collision theory
Cold collisions of ground state oxygen molecules with Helium have been
investigated in a wide range of cold collision energies (from 1 K up to 10
K) treating the oxygen molecule first as a rigid rotor and then introducing the
vibrational degree of freedom. The comparison between the two models shows that
at low energies the rigid rotor approximation is very accurate and able to
describe all the dynamical features of the system. The comparison between the
two models has also been extended to cases where the interaction potential He -
O is made artificially stronger. In this case vibration can perturb rate
constants, but fine-tuning the rigid rotor potential can alleviate the
discrepancies between the two models.Comment: 11 pages, 3 figure
On the role of the magnetic dipolar interaction in cold and ultracold collisions: Numerical and analytical results for NH() + NH()
We present a detailed analysis of the role of the magnetic dipole-dipole
interaction in cold and ultracold collisions. We focus on collisions between
magnetically trapped NH molecules, but the theory is general for any two
paramagnetic species for which the electronic spin and its space-fixed
projection are (approximately) good quantum numbers. It is shown that dipolar
spin relaxation is directly associated with magnetic-dipole induced avoided
crossings that occur between different adiabatic potential curves. For a given
collision energy and magnetic field strength, the cross-section contributions
from different scattering channels depend strongly on whether or not the
corresponding avoided crossings are energetically accessible. We find that the
crossings become lower in energy as the magnetic field decreases, so that
higher partial-wave scattering becomes increasingly important \textit{below} a
certain magnetic field strength. In addition, we derive analytical
cross-section expressions for dipolar spin relaxation based on the Born
approximation and distorted-wave Born approximation. The validity regions of
these analytical expressions are determined by comparison with the NH + NH
cross sections obtained from full coupled-channel calculations. We find that
the Born approximation is accurate over a wide range of energies and field
strengths, but breaks down at high energies and high magnetic fields. The
analytical distorted-wave Born approximation gives more accurate results in the
case of s-wave scattering, but shows some significant discrepancies for the
higher partial-wave channels. We thus conclude that the Born approximation
gives generally more meaningful results than the distorted-wave Born
approximation at the collision energies and fields considered in this work.Comment: Accepted by Eur. Phys. J. D for publication in Special Issue on Cold
Quantum Matter - Achievements and Prospects (2011
Volume element structure and roton-maxon-phonon excitations in superfluid helium beyond the Gross-Pitaevskii approximation
We propose a theory which deals with the structure and interactions of volume
elements in liquid helium II. The approach consists of two nested models linked
via parametric space. The short-wavelength part describes the interior
structure of the fluid element using a non-perturbative approach based on the
logarithmic wave equation; it suggests the Gaussian-like behaviour of the
element's interior density and interparticle interaction potential. The
long-wavelength part is the quantum many-body theory of such elements which
deals with their dynamics and interactions. Our approach leads to a unified
description of the phonon, maxon and roton excitations, and has noteworthy
agreement with experiment: with one essential parameter to fit we reproduce at
high accuracy not only the roton minimum but also the neighboring local maximum
as well as the sound velocity and structure factor.Comment: 9 pages, 6 figure
BCS and BEC p-wave pairing in Bose-Fermi gases
The pairing of fermionic atoms in a mixture of atomic fermion and boson gases
at zero temperature is investigated. The attractive interaction between
fermions, that can be induced by density fluctuations of the bosonic
background, can give rise to a superfluid phase in the Fermi component of the
mixture. The atoms of both species are assumed to be in only one internal
state, so that the pairing of fermions is effective only in odd-l channels. No
assumption about the value of the ratio between the Fermi velocity and the
sound velocity in the Bose gas is made in the derivation of the energy gap
equation. The gap equation is solved without any particular "ansatz" for the
pairing field or the effective interaction. The p-wave superfluidity is studied
in detail. By increasing the strength and/or decreasing the range of the
effective interaction a transition of the fermion pairing regime, from the
Bardeen-Cooper-Schrieffer state to a system of tightly bound couples can be
realized. These composite bosons behave as a weakly-interacting Bose-Einstein
condensate.Comment: 14 pages, 6 eps-figures. To be published in European Physical Journal
Impact of the phonon coupling on the dipole strength and radiative neutron capture
info:eu-repo/semantics/publishe
Renormalized RPA at finite temperature
info:eu-repo/semantics/publishe
Impact of the phonon coupling on the radiative neutron capture
info:eu-repo/semantics/publishe