2,088 research outputs found
Adiabatic hyperspherical study of triatomic helium systems
The 4He3 system is studied using the adiabatic hyperspherical representation.
We adopt the current state-of-the-art helium interaction potential including
retardation and the nonadditive three-body term, to calculate all low-energy
properties of the triatomic 4He system. The bound state energies of the 4He
trimer are computed as well as the 4He+4He2 elastic scattering cross sections,
the three-body recombination and collision induced dissociation rates at finite
temperatures. We also treat the system that consists of two 4He and one 3He
atoms, and compute the spectrum of the isotopic trimer 4He2 3He, the 3He+4He2
elastic scattering cross sections, the rates for three-body recombination and
the collision induced dissociation rate at finite temperatures. The effects of
retardation and the nonadditive three-body term are investigated. Retardation
is found to be significant in some cases, while the three-body term plays only
a minor role for these systems.Comment: 24 pages 6 figures Submitted to Physical Review
Strong and radiative decays of the Ds0*(2317) meson in the DK-molecule picture
We consider a possible interpretation of the new charm-strange meson
Ds0*(2317) as a hadronic molecule - a bound state of D and K mesons. Using an
effective Lagrangian approach we calculate the strong Ds0* to Ds pi0 and
radiative Ds0* to Ds* gamma decays. A new impact related to the DK molecular
structure of the Ds0*(2317) meson is that the presence of u(d) quarks in the D
and K mesons gives rise to a direct strong isospin-violating transition Ds0* to
Ds pi0 in addition to the decay mechanism induced by eta-pi0 mixing considered
previously. We show that the direct transition dominates over the eta-pi0
mixing transition in the Ds0* to Ds pi0 decay. Our results for the partial
decay widths are consistent with previous calculations.Comment: 22 pages, 4 figures, accepted for publication in Phys. Rev.
The structure of the atomic helium trimers: Halos and Efimov states
The Faddeev equations for the atomic helium-trimer systems are solved
numerically with high accuracy both for the most sophisticated realistic
potentials available and for simple phenomenological potentials. An efficient
numerical procedure is described. The large-distance asymptotic behavior,
crucial for weakly bound three-body systems, is described almost analytically
for arbitrary potentials. The Efimov effect is especially considered. The
geometric structures of the bound states are quantitatively investigated. The
accuracy of the schematic models and previous computations is comparable, i.e.
within 20% for the spatially extended states and within 40% for the smaller
^4He-trimer ground state.Comment: 32 pages containing 7 figures and 6 table
Production of three-body Efimov molecules in an optical lattice
We study the possibility of associating meta-stable Efimov trimers from three
free Bose atoms in a tight trap realised, for instance, via an optical lattice
site or a microchip. The suggested scheme for the production of these molecules
is based on magnetically tunable Feshbach resonances and takes advantage of the
Efimov effect in three-body energy spectra. Our predictions on the energy
levels and wave functions of three pairwise interacting 85Rb atoms rely upon
exact solutions of the Faddeev equations and include the tightly confining
potential of an isotropic harmonic atom trap. The magnetic field dependence of
these energy levels indicates that it is the lowest energetic Efimov trimer
state that can be associated in an adiabatic sweep of the field strength. We
show that the binding energies and spatial extents of the trimer molecules
produced are comparable, in their magnitudes, to those of the associated
diatomic Feshbach molecule. The three-body molecular state follows Efimov's
scenario when the pairwise attraction of the atoms is strengthened by tuning
the magnetic field strength.Comment: 21 pages, 8 figures (final version
Small mass- and trap-imbalanced two-component Fermi systems
Motivated by the prospect of optical lattice experiments with two-component
Fermi gases consisting of different atomic species such as Li and K, we
calculate the energies for N fermions under harmonic confinement as a function
of the mass- and trap-imbalance, i.e., as a function of the ratio between the
masses and frequencies of species one and two, using microscopic approaches.
Our energies for N=2 through 6 can be used to determine the energetically most
favorable configuration for a given number of atoms per species of a deep
lattice in which each lattice site is approximately harmonic and in which
tunneling between neighboring sites can be neglected. Furthermore, our energies
determine one of the input parameters, namely the onsite interaction strength,
of the corresponding lattice Hamiltonian. We also determine and interpret the
excitation gap for unequal-mass systems with up to N=13 atoms for equal
oscillator lengths.Comment: 13 pages, 9 figure
BEC-BCS Crossover of a Trapped Two-Component Fermi Gas with Unequal Masses
We determine the energetically lowest lying states in the BEC-BCS crossover
regime of s-wave interacting two-component Fermi gases under harmonic
confinement by solving the many-body Schrodinger equation using two distinct
approaches. Essentially exact basis set expansion techniques are applied to
determine the energy spectrum of systems with N=4 fermions. Fixed-node
diffusion Monte Carlo methods are applied to systems with up to N=20 fermions,
and a discussion of different guiding functions used in the Monte Carlo
approach to impose the proper symmetry of the fermionic system is presented.
The energies are calculated as a function of the s-wave scattering length a_s
for N=2-20 fermions and different mass ratios \kappa of the two species. On the
BEC and BCS sides, our energies agree with analytically-determined first-order
correction terms. We extract the scattering length and the effective range of
the dimer-dimer system up to \kappa = 20. Our energies for the
strongly-interacting trapped system in the unitarity regime show no shell
structure, and are well described by a simple expression, whose functional form
can be derived using the local density approximation, with one or two
parameters. The universal parameter \xi for the trapped system for various
\kappa is determined, and comparisons with results for the homogeneous system
are presented.Comment: 11 pages, 6 figures, extended versio
Analytic Confinement and Regge Trajectories
A simple relativistic quantum field model with the Yukawa-type interaction is
considered to demonstrate that the analytic confinement of the constituent
("quarks") and carrier ("gluons") particles explains qualitatively the basic
dynamical properties of the spectrum of mesons considered as two-particle
stable bound states of quarks and gluons: the quarks and gluons are confined,
the glueballs represent bound states of massless gluons, the masses of mesons
are larger than the sum of the constituent quark masses and the Regge
trajectories of mesonic orbital excitations are almost linear.Comment: RevTeX, 16 pages, 3 figures and 2 table
Illustration of universal relations for trapped four-fermion system with arbitrary s-wave scattering length
A two-component four-fermion system with equal masses, interspecies s-wave
scattering length a and vanishing intraspecies interactions under external
spherically symmetric harmonic confinement is considered. Using a correlated
Gaussian basis set expansion approach, we determine the energies and various
structural properties of the energetically lowest-lying gas-like state
throughout the crossover for various ranges of the underlying two-body
potential. Extrapolating to the zero-range limit, our numerical results show
explicitly that the total energy, the trap energy as well as certain aspects of
the pair distribution function and of the momentum distribution are related
through the so-called integrated contact intensity I(a). Furthermore, it is
shown explicitly that the total energy and the trap energy are related through
a generalized virial theorem that accounts for a non-zero range.Comment: 9 figures with several subfigure
Collisional stability of a three-component degenerate Fermi gas
We report on the creation of a degenerate Fermi gas consisting of a balanced
mixture of atoms in three different hyperfine states of Li. This new system
consists of three distinguishable Fermions with different and tunable
interparticle scattering lengths , and . We are able
to prepare samples containing atoms in each state at a
temperature of about nK, which corresponds to . We
investigated the collisional stability of the gas for magnetic fields between 0
and 600 G and found a prominent loss feature at 130 G. From lifetime
measurements we determined three-body loss coefficients, which vary over nearly
three orders of magnitude
On orientational relief of inter-molecular potential and the structure of domain walls in fullerite C60
A simple planar model for an orientational ordering of threefold molecules on
a triangular lattice modelling a close-packed (111) plane of fullerite is
considered. The system has 3-sublattice ordered ground state which includes 3
different molecular orientations. There exist 6 kinds of orientational domains,
which are related with a permutation or a mirror symmetry. Interdomain walls
are found to be rather narrow.
The model molecules have two-well orientational potential profiles, which are
slightly effected by a presence of a straight domain wall. The reason is a
stronger correlation between neighbour molecules in triangular lattice versus
previously considered square lattice
A considerable reduction (up to one order) of orientational interwell
potential barrier is found in the core regions of essentially two-dimentional
potential defects, such as a three-domain boundary or a kink in the domain
wall. For ultimately uncorrelated nearest neighbours the height of the
interwell barrier can be reduced even by a factor of 100.Comment: 11 pages, 13 figures, LaTeX, to appear in Low Temperature Physic
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