4,784 research outputs found
Correlations in Ultracold Trapped Few-Boson Systems: Transition from Condensation to Fermionization
We study the correlation properties of the ground states of few ultracold
bosons, trapped in double wells of varying barrier height in one dimension.
Extending previous results on the signature of the transition from a
Bose-condensed state via fragmentation to the hard-core limit, we provide a
deeper understanding of that transition by relating it to the loss of coherence
in the one-body density matrix and to the emerging long-range tail in the
momentum spectrum. These are accounted for in detail by discussing the natural
orbitals and their occupations. Our discussion is complemented by an analysis
of the two-body correlation function.Comment: 22 pages, 7 figure
Excitations of Few-Boson Systems in 1-D Harmonic and Double Wells
We examine the lowest excitations of one-dimensional few-boson systems
trapped in double wells of variable barrier height. Based on a numerically
exact multi-configurational method, we follow the whole pathway from the
non-interacting to the fermionization limit. It is shown how, in a purely
harmonic trap, the initially equidistant, degenerate levels are split up due to
interactions, but merge again for strong enough coupling. In a double well, the
low-lying spectrum is largely rearranged in the course of fermionization,
exhibiting level adhesion and (anti-)crossings. The evolution of the underlying
states is explained in analogy to the ground-state behavior. Our discussion is
complemented by illuminating the crossover from a single to a double well.Comment: 11 pages, 10 figure
Quantum dynamics of two bosons in an anharmonic trap: Collective vs internal excitations
This work deals with the effects of an anharmonic trap on an interacting
two-boson system in one dimension. Our primary focus is on the role of the
induced coupling between the center of mass and the relative motion as both
anharmonicity and the (repulsive) interaction strength are varied. The ground
state reveals a strong localization in the relative coordinate, counteracting
the tendency to fragment for stronger repulsion. To explore the quantum
dynamics, we study the system's response upon (i) exciting the harmonic ground
state by continuously switching on an additional anharmonicity, and (ii)
displacing the center of mass, this way triggering collective oscillations. The
interplay between collective and internal dynamics materializes in the collapse
of oscillations, which are explained in terms of few-mode models.Comment: 8 pages, 7 figure
Lattice Universes in 2+1-dimensional gravity
Lattice universes are spatially closed space-times of spherical topology in
the large, containing masses or black holes arranged in the symmetry of a
regular polygon or polytope. Exact solutions for such spacetimes are found in
2+1 dimensions for Einstein gravity with a non-positive cosmological constant.
By means of a mapping that preserves the essential nature of geodesics we
establish analogies between the flat and the negative curvature cases. This map
also allows treatment of point particles and black holes on a similar footing.Comment: 14 pages 7 figures, to appear in Festschrift for Vince Moncrief (CQG
The twist-2 Compton operator and its hidden Wandzura-Wilczek and Callan-Gross relations
Power corrections for virtual Compton scattering at leading twist are
etermined at operator level. From the complete off-cone representation of the
twist-2 Compton operator integral representations for the trace, antisymmetric
and symmetric part of that operator are derived. The operator valued invariant
functions are written in terms of iterated operators and may lead to
interrelations. For matrix elements they go over into relations for generalized
parton distributions. -- Reducing to the s-channel relevant part one gets
operator pre-forms of the Wandzura-Wilczek and the (target mass corrected)
Callan-Gross relations whose structure is exactly the same as known from the
case of deep inelastic scattering; taking non-forward matrix elements one
reproduces earlier results [B. Geyer, D. Robaschik and J. Eilers, Nucl. Phys. B
704 (2005) 279] for the absorptive part of the virtual Compton amplitude. --
All these relations, obtained without any approximation or using equations of
motion, are determined solely by the twist-2 structure of the underlying
operator and, therefore, are purely of geometric origin.Comment: 13 pages, Latex 2e, Introduction shortend, Section Prerequisites
added, more obvious formulations used, some formulas rewritten as well as
added, conclusions extended, references added. Final version as appearing in
PR
Adding Salt to an Aqueous Solution of t-Butanol: Is Hydrophobic Association Enhanced or Reduced?
Recent neutron scattering experiments on aqueous salt solutions of
amphiphilic t-butanol by Bowron and Finney [Phys. Rev. Lett. {\bf 89}, 215508
(2002); J. Chem. Phys. {\bf 118}, 8357 (2003)] suggest the formation of
t-butanol pairs, bridged by a chloride ion via
hydrogen-bonds, and leading to a reduced number of intermolecular hydrophobic
butanol-butanol contacts. Here we present a joint experimental/theoretical
study on the same system, using a combination of molecular dynamics simulations
and nuclear magnetic relaxation measurements. Both theory and experiment
clearly support the more intuitive scenario of an enhanced number of
hydrophobic contacts in the presence of the salt, as it would be expected for
purely hydrophobic solutes [J. Phys. Chem. B {\bf 107}, 612 (2003)]. Although
our conclusions arrive at a structurally completely distinct scenario, the
molecular dynamics simulation results are within the experimental errorbars of
the Bowron and Finney work.Comment: 15 pages twocolumn revtex, 11 figure
New supersymmetric AdS4 type II vacua
Building on our recent results on dynamic SU(3)xSU(3) structures we present a
set of sufficient conditions for supersymmetric AdS4xM6 backgrounds of type
IIA/IIB supergravity. These conditions ensure that the background solves,
besides the supersymmetry equations, all the equations of motion of type II
supergravity. The conditions state that the internal manifold is locally a
codimension-one foliation such that the five dimensional leaves admit a
Sasaki-Einstein structure. In type IIA the supersymmetry is N=2, and the total
six-dimensional internal space is locally an S^2 bundle over a four-dimensional
Kaehler-Einstein base; in IIB the internal space is the direct product of a
circle and a five-dimensional squashed Sasaki-Einstein manifold. Given any
five-dimensional Sasaki-Einstein manifold we construct the corresponding
families of type IIA/IIB vacua. The precise profiles of all the fields are
determined at the solution and depend on whether one is in IIA or in IIB. In
particular the background does not contain any sources, all fluxes (including
the Romans mass in IIA) are generally non-zero, and the dilaton and warp factor
are non-constant.Comment: 19 pages; clarifications added, version to appear in JHE
Gravitational wave detectors based on matter wave interferometers (MIGO) are no better than laser interferometers (LIGO)
We show that a recent claim that matter wave interferometers have a much
higher sensitivity than laser interferometers for a comparable physical setup
is unfounded. We point out where the mistake in the earlier analysis is made.
We also disprove the claim that only a description based on the geodesic
deviation equation can produce the correct physical result. The equations for
the quantum dynamics of non-relativistic massive particles in a linearly
perturbed spacetime derived here are useful for treating a wider class of
related physical problems. A general discussion on the use of atom
interferometers for the detection of gravitational waves is also provided.Comment: 16 pages, REVTeX4; minor changes, one figure and a few references
were added, an additional appendix was included where we explain why,
contrary to the claims in gr-qc/0409099, the effects due to the reflection
off the mirrors cancel out in the final result for the phase shif
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