29,400 research outputs found
Density profiles and collective modes of a Bose-Einstein condensate with light-induced spin-orbit coupling
The phases of a Bose-Einstein condensate (BEC) with light-induced spin-orbit
coupling (SOC) are studied within the mean-field approximation. The mixed BEC
phase, in which the system condenses in a superposition of two plane wave
states, is found to be stable for sufficiently small light-atom coupling,
becoming unstable in a continuous fashion with increasing light-atom coupling.
The structure of the phase diagram at fixed chemical potential for bosons with
SOC is shown to imply an unusual density dependence for a trapped mixed BEC
phase, with the density of one dressed spin state increasing with increasing
radius, providing a unique experimental signature of this state. The collective
Bogoliubov sound mode is shown to also provide a signature of the mixed BEC
state, vanishing as the boundary to the regime of phase separation is
approached.Comment: 9 pages, 4 figures. Published Versio
A self-consistent Hartree-Fock approach for interacting bosons in optical lattices
A theoretical study of interacting bosons in a periodic optical lattice is
presented. Instead of the commonly used tight-binding approach (applicable near
the Mott insulating regime of the phase diagram), the present work starts from
the exact single-particle states of bosons in a cubic optical lattice,
satisfying the Mathieu equation, an approach that can be particularly useful at
large boson fillings. The effects of short-range interactions are incorporated
using a self-consistent Hartree-Fock approximation, and predictions for
experimental observables such as the superfluid transition temperature,
condensate fraction, and boson momentum distribution are presented.Comment: 12 pages, 15 figure file
Critical behaviour of a spin-tube model in a magnetic field
We show that the low-energy physics of the spin-tube model in presence of a
critical magnetic field can be described by a broken SU(3) spin chain. Using
the Lieb-Schultz-Mattis Theorem we characterize the possible magnetization
plateaus and study the critical behavior in the region of transition between
the plateaus m=1/2 and m=3/2 by means of renormalization group calculations
performed on the bosonized effective continuum field theory. We show that in
certain regions of the parameter space of the effective theory the system
remains gapless, and we compute the spin-spin correlation functions in these
regions. We also discuss the possibility of a plateau at m=1, and show that
although there exists in the continuum theory a term that might cause the
appearance of a plateau there, such term is unlikely to be relevant. This
conjecture is proved by DMRG techniques. The modifications of the three-leg
ladder Hamiltonian that might show plateaus at m =1,5/6,7/6 are discussed, and
we give the expected form of correlation functions on the m=1 plateau.Comment: RevTeX, 43 pages, 5 EPS figure
Strain-dependent solid surface stress and the stiffness of soft contacts
Surface stresses have recently emerged as a key player in the mechanics of
highly compliant solids. The classic theories of contact mechanics describe
adhesion with a compliant substrate as a competition between surface energies
driving deformation to establish contact and bulk elasticity resisting this.
However, it has recently been shown that surface stresses provide an additional
restoring force that can compete with and even dominate over elasticity in
highly compliant materials, especially when length scales are small compared to
the ratio of the surface stress to the elastic modulus, . Here, we
investigate experimentally the contribution of surface stresses to the force of
adhesion. We find that the elastic and capillary contributions to the adhesive
force are of similar magnitude, and that both are required to account for
measured adhesive forces between rigid silica spheres and compliant, silicone
gels. Notably, the strain-dependence of the solid surface stress contributes
significantly to the stiffness of soft solid contacts.Comment: 6 pages, 3 figure
Characteristics of profiles of gamma-ray burst pulses associated with the Doppler effect of fireballs
In this paper, we derive in a much detail the formula of count rates, in
terms of the integral of time, of gamma-ray bursts in the framework of
fireballs, where the Doppler effect of the expanding fireball surface is the
key factor to be concerned. Effects arising from the limit of the time delay
due to the limited regions of the emitting areas in the fireball surface and
other factors are investigated. Our analysis shows that the formula of the
count rate of fireballs can be expressed as a function of which is the
observation time scale relative to the dynamical time scale of the fireball.
The profile of light curves of fireballs depends only on the relative time
scale, entirely independent of the real time scale and the real size of the
objects. It displays in detail how a cutoff tail, or a turn over, feature
(called a cutoff tail problem) in the decay phase of a light curve can be
formed. This feature is a consequence of a hot spot in the fireball surface,
moving towards the observer, and was observed in a few cases previously. By
performing fits to the count rate light curves of six sample sources, we show
how to obtain some physical parameters from the observed profile of the count
rate of GRBs. In addition, the analysis reveals that the Doppler effect of
fireballs could lead to a power law relationship between the of pulses
and energy, which were observed previously by many authors.Comment: 38 pages, 10 figures; accepted for publication in ApJ (10 December
2004, v617
Jet Modification in a Brick of QGP Matter
We have implemented the LPM effect into a microscopic transport model with
partonic degrees of freedom by following the algorithm of Zapp & Wiedemann. The
Landau-Pomeranchuk-Migdal (LPM) effect is a quantum interference process that
modifies the emission of radiation in the presence of a dense medium. In QCD
this results in a quadratic length dependence for radiative energy loss. This
is an important effect for the modification of jets by their passage through
the QGP.
We verify the leading parton energy loss in the model against the leading
order Baier-Dokshitzer-Mueller-Peigne-Schiff-Zakharov (BDMPS-Z) result.
We apply our model to the recent observations of the modification of di-jets
at the LHC.Comment: Presented at Panic 1
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