14,774 research outputs found
Volume Dependence of Bound States with Angular Momentum
We derive general results for the mass shift of bound states with angular
momentum l >= 1 in a finite periodic volume. Our results have direct
applications to lattice simulations of hadronic molecules as well as atomic
nuclei. While the binding of S-wave bound states increases at finite volume, we
show that the binding of P-wave bound states decreases. The mass shift for
D-wave bound states as well as higher partial waves depends on the
representation of the cubic rotation group. Nevertheless, the
multiplet-averaged mass shift for any angular momentum l can be expressed in a
simple form, and the sign of the shift alternates for even and odd l. We verify
our analytical results with explicit numerical calculations. We also show
numerically that similar volume corrections appear in three-body bound states.Comment: 4 pages, 3 figures, final versio
High-spin intruder states in the fp shell nuclei and isoscalar proton-neutron correlations
We perform a systematic shell-model and mean-field study of fully-aligned,
high-spin f_{7/2}^{n} seniority isomers and d_{3/2}^{-1} f_{7/2}^{n+1} intruder
states in the A~44 nuclei from the lower-fp shell. The shell-model calculations
are performed in the full sdfp configuration space allowing 1p-1h cross-shell
excitations. The self-consistent mean-field calculations are based on the
Hartree-Fock approach with the Skyrme energy density functional that reproduces
empirical Landau parameters. While there is a nice agreement between
experimental and theoretical relative energies of fully-aligned states in N>Z
nuclei, this is no longer the case for the N=Z systems. The remaining deviation
from the data is attributed to the isoscalar proton-neutron correlations. It is
also demonstrated that the Coulomb corrections at high spins noticeably depend
on the choice of the energy density functional.Comment: 4 pages. submitted to Phys. Rev. Let
Ab initio lattice results for Fermi polarons in two dimensions
We investigate the attractive Fermi polaron problem in two dimensions using
non-perturbative Monte Carlo simulations. We introduce a new Monte Carlo
algorithm called the impurity lattice Monte Carlo method. This algorithm
samples the path integral in a computationally efficient manner and has only
small sign oscillations for systems with a single impurity. As a benchmark of
the method, we calculate the universal polaron energy in three dimensions in
the scale-invariant unitarity limit and find agreement with published results.
We then present the first fully non-perturbative calculations of the polaron
energy in two dimensions and density correlations between the impurity and
majority particles in the limit of zero range interactions. We find evidence
for a smooth crossover transition from fermionic quasiparticle to molecular
state as a function of interaction strength.Comment: Includes new results on density-density correlations. Final version
as will appear in Phys. Rev. Let
Renormalization of Drift and Diffusivity in Random Gradient Flows
We investigate the relationship between the effective diffusivity and
effective drift of a particle moving in a random medium. The velocity of the
particle combines a white noise diffusion process with a local drift term that
depends linearly on the gradient of a gaussian random field with homogeneous
statistics. The theoretical analysis is confirmed by numerical simulation. For
the purely isotropic case the simulation, which measures the effective drift
directly in a constant gradient background field, confirms the result
previously obtained theoretically, that the effective diffusivity and effective
drift are renormalized by the same factor from their local values. For this
isotropic case we provide an intuitive explanation, based on a {\it spatial}
average of local drift, for the renormalization of the effective drift
parameter relative to its local value. We also investigate situations in which
the isotropy is broken by the tensorial relationship of the local drift to the
gradient of the random field. We find that the numerical simulation confirms a
relatively simple renormalization group calculation for the effective
diffusivity and drift tensors.Comment: Latex 16 pages, 5 figures ep
Perturbation theory for the effective diffusion constant in a medium of random scatterer
We develop perturbation theory and physically motivated resummations of the
perturbation theory for the problem of a tracer particle diffusing in a random
media. The random media contains point scatterers of density uniformly
distributed through out the material. The tracer is a Langevin particle
subjected to the quenched random force generated by the scatterers. Via our
perturbative analysis we determine when the random potential can be
approximated by a Gaussian random potential. We also develop a self-similar
renormalisation group approach based on thinning out the scatterers, this
scheme is similar to that used with success for diffusion in Gaussian random
potentials and agrees with known exact results. To assess the accuracy of this
approximation scheme its predictions are confronted with results obtained by
numerical simulation.Comment: 22 pages, 6 figures, IOP (J. Phys. A. style
Diffusion of active tracers in fluctuating fields
The problem of a particle diffusion in a fluctuating scalar field is studied.
In contrast to most studies of advection diffusion in random fields we analyze
the case where the particle position is also coupled to the dynamics of the
field. Physical realizations of this problem are numerous and range from the
diffusion of proteins in fluctuating membranes and the diffusion of localized
magnetic fields in spin systems. We present exact results for the diffusion
constant of particles diffusing in dynamical Gaussian fields in the adiabatic
limit where the field evolution is much faster than the particle diffusion. In
addition we compute the diffusion constant perturbatively, in the weak coupling
limit where the interaction of the particle with the field is small, using a
Kubo-type relation. Finally we construct a simple toy model which can be solved
exactly.Comment: 13 pages, 1 figur
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Number of Pages: 2Integrative BiologyGeological Science
Pairing Reentrance Phenomenon in Heated Rotating Nuclei in the Shell Model Monte Carlo Approach
Rotational motion of heated 72-Ge is studied within the microscopic Shell
Model Monte Carlo approach. We investigate the the angular momentum alignment
and nuclear pairing correlations associated with J-pi Cooper pairs as a
function of the rotational frequency and temperature. The reentrance of pairing
correlations with temperature is predicted at high rotational frequencies. It
manifests itself through the anomalous behavior of specific heat and level
density.Comment: 4 pages; 4 figure
Shell Model Monte Carlo Investigation of Rare Earth Nuclei
We utilize the Shell Model Monte Carlo (SMMC) method to study the structure
of rare earth nuclei. This work demonstrates the first systematic ``full
oscillator shell plus intruder'' calculations in such heavy nuclei. Exact
solutions of a pairing plus quadrupole hamiltonian are compared with mean field
and SPA approximations in several Dysprosium isotopes from A=152-162, including
the odd mass A=153. Basic properties of these nuclei at various temperatures
and spin are explored. These include energy, deformation, moments of inertia,
pairing channel strengths, band crossing, and evolution of shell model
occupation numbers. Exact level densities are also calculated and, in the case
of 162 Dy, compared with experimental data.Comment: 40 pages; 24 figures; 2 tables. Update includes correction of figure
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