955 research outputs found
The Scattered Disk as the source of the Jupiter Family comets
The short period Jupiter family comets (JFCs) are thought to originate in the
Kuiper Belt; specifically, a dynamical subclass of the Kuiper Belt known as the
`scattered disk' is argued to be the dominant source of JFCs. However, the best
estimates from observational surveys indicate that this source may fall short
by more than two orders of magnitude the estimates obtained from theoretical
models of the dynamical evolution of Kuiper belt objects into JFCs. We
re-examine the scattered disk as a source of the JFCs and make a rigorous
estimate of the discrepancy. We find that the uncertainties in the dynamical
models combined with a change in the size distribution function of the
scattered disk at faint magnitudes (small sizes) beyond the current
observational limit offer a possible but problematic resolution to the
discrepancy. We discuss several other possibilities: that the present
population of JFCs is a large fluctuation above their long term average, that
larger scattered disk objects tidally break-up into multiple fragments during
close planetary encounters as their orbits evolve from the trans-Neptune zone
to near Jupiter, or that there are alternative source populations that
contribute significantly to the JFCs. Well-characterized observational
investigations of the Centaurs, objects that are transitioning between the
trans-Neptune Kuiper belt region and the inner solar system, can test the
predictions of the non-steady state and the tidal break-up hypotheses. The
classical and resonant classes of the Kuiper belt are worth re-consideration as
significant additional or alternate sources of the JFCs.Comment: 33 pages, 6 figures. Revised Content. To be published in The
Astrophysical Journa
Bose-Einstein condensation of trapped interacting spin-1 atoms
We investigate Bose-Einstein condensation of trapped spin-1 atoms with
ferromagnetic or antiferromagnetic two-body contact interactions. We adopt the
mean field theory and develop a Hartree-Fock-Popov type approximation in terms
of a semiclassical two-fluid model. For antiferromagnetic interactions, our
study reveals double condensations as atoms in the state never seem
to condense under the constraints of both the conservation of total atom number
and magnetization . For ferromagnetic interactions, however, triple
condensations can occur. Our results can be conveniently understood in terms of
the interplay of three factors: (anti) ferromagnetic atom-atom interactions,
conservation, and the miscibilities between and among different condensed
components.Comment: RevTex 4, 9 pages, 5 eps figures, to appear in Phys. Rev. A, vol 70,
p
Dilute Bose gas with correlated disorder: A Path Integral Monte Carlo study
We investigate the thermodynamic properties of a dilute Bose gas in a
correlated random potential using exact path integral Monte Carlo methods. The
study is carried out in continuous space and disorder is produced in the
simulations by a 3D speckle pattern with tunable intensity and correlation
length. We calculate the shift of the superfluid transition temperature due to
disorder and we highlight the role of quantum localization by comparing the
critical chemical potential with the classical percolation threshold. The
equation of state of the gas is determined in the regime of strong disorder,
where superfluidity is suppressed and the normal phase exists down to very low
temperatures. We find a dependence of the energy in agreement with the
expected behavior in the Bose glass phase. We also discuss the major role
played by the disorder correlation length and we make contact with a
Hartree-Fock mean-field approach that holds valid if the correlation length is
very large. The density profiles are analyzed as a function of temperature and
interaction strength. Effects of localization and the depletion of the order
parameter are emphasized in the comparison between local condensate and total
density. At very low temperature we find that the energy and the particle
distribution of the gas are very well described by the T=0 Gross-Pitaevskii
theory even in the regime of very strong disorder.Comment: 27 pages, 20 figure
Anomalous fluctuations of the condensate in interacting Bose gases
We find that the fluctuations of the condensate in a weakly interacting Bose
gas confined in a box of volume follow the law . This anomalous behaviour arises from the occurrence of infrared
divergencies due to phonon excitations and holds also for strongly correlated
Bose superfluids. The analysis is extended to an interacting Bose gas confined
in a harmonic trap where the fluctuations are found to exhibit a similar
anomaly.Comment: 4 pages, RevTe
Equation of state of an interacting Bose gas at finite temperature: a Path Integral Monte Carlo study
By using exact Path Integral Monte Carlo methods we calculate the equation of
state of an interacting Bose gas as a function of temperature both below and
above the superfluid transition. The universal character of the equation of
state for dilute systems and low temperatures is investigated by modeling the
interatomic interactions using different repulsive potentials corresponding to
the same s-wave scattering length. The results obtained for the energy and the
pressure are compared to the virial expansion for temperatures larger than the
critical temperature. At very low temperatures we find agreement with the
ground-state energy calculated using the diffusion Monte Carlo method.Comment: 7 pages, 6 figure
Quasi-one-dimensional Bose gases with large scattering length
Bose gases confined in highly-elongated harmonic traps are investigated over
a wide range of interaction strengths using quantum Monte Carlo techniques. We
find that the properties of a Bose gas under tight transverse confinement are
well reproduced by a 1d model Hamiltonian with contact interactions. We point
out the existence of a unitary regime, where the properties of the quasi-1d
Bose gas become independent of the actual value of the 3d scattering length. In
this unitary regime, the energy of the system is well described by a hard rod
equation of state. We investigate the stability of quasi-1d Bose gases with
positive and negative 3d scattering length.Comment: 5 pages, 3 figure
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