166 research outputs found
Free expansion of lowest Landau level states of trapped atoms: a wavefunction microscope
We show that for any lowest-Landau-level state of a trapped, rotating,
interacting Bose gas, the particle distribution in coordinate space in a free
expansion (time of flight) experiment is related to that in the trap at the
time it is turned off by a simple rescaling and rotation. When the
lowest-Landau-level approximation is valid, interactions can be neglected
during the expansion, even when they play an essential role in the ground state
when the trap is present. The correlations in the density in a single snapshot
can be used to obtain information about the fluid, such as whether a transition
to a quantum Hall state has occurred.Comment: 5 pages, no figures. v2: discussion of neglect of interactions during
expansion improved, refs adde
Rotating spin-1 bosons in the lowest Landau level
We present results for the ground states of a system of spin-1 bosons in a
rotating trap. We focus on the dilute, weakly interacting regime, and restrict
the bosons to the quantum states in the lowest Landau level (LLL) in the plane
(disc), sphere or torus geometries. We map out parts of the zero temperature
phase diagram, using both exact quantum ground states and LLL mean field
configurations. For the case of a spin-independent interaction we present exact
quantum ground states at angular momentum . For general values of the
interaction parameters, we present mean field studies of general ground states
at slow rotation and of lattices of vortices and skyrmions at higher rotation
rates. Finally, we discuss quantum Hall liquid states at ultra-high rotation.Comment: 24 pages, 14 figures, RevTe
Spin dynamics simulations of the magnetic dynamics of RbMnF and direct comparison with experiment
Spin-dynamics techniques have been used to perform large-scale simulations of
the dynamic behavior of the classical Heisenberg antiferromagnet in simple
cubic lattices with linear sizes . This system is widely recognized
as an appropriate model for the magnetic properties of RbMnF.
Time-evolutions of spin configurations were determined numerically from coupled
equations of motion for individual spins using a new algorithm implemented by
Krech {\it etal}, which is based on fourth-order Suzuki-Trotter decompositions
of exponential operators. The dynamic structure factor was calculated from the
space- and time-displaced spin-spin correlation function. The crossover from
hydrodynamic to critical behavior of the dispersion curve and spin-wave
half-width was studied as the temperature was increased towards the critical
temperature. The dynamic critical exponent was estimated to be , which is slightly lower than the dynamic scaling prediction, but in
good agreement with a recent experimental value. Direct, quantitative
comparisons of both the dispersion curve and the lineshapes obtained from our
simulations with very recent experimental results for RbMnF are presented.Comment: 30 pages, RevTex, 9 figures, to appear in PR
Dynamics of Baryons from String Theory and Vector Dominance
We consider a holographic model of QCD from string theory, a la Sakai and
Sugimoto, and study baryons. In this model, mesons are collectively realized as
a five-dimensional \ Yang-Mills field and baryons
are classically identified as solitons with a unit Pontryagin number
and electric charges. The soliton is shown to be very small in the large
't Hooft coupling limit, allowing us to introduce an effective field . Its coupling to the mesons are dictated by the soliton structure, and
consists of a direct magnetic coupling to the field strength as well
as a minimal coupling to the gauge field. Upon the dimensional
reduction, this effective action reproduces all interaction terms between
nucleons and an infinite tower of mesons in a manner consistent with the large
expansion. We further find that all electromagnetic interactions, as
inferred from the same effective action via a holographic prescription, are
mediated by an infinite tower of vector mesons, rendering the baryon
electromagnetic form factors completely vector-dominated as well. We estimate
nucleon-meson couplings and also the anomalous magnetic moments, which compare
well with nature.Comment: 65pages, 3 figures, vector mesons and axial-vector mesons are now
canonically normalized (comparisons with data and conclusions unaffected
Nonconstant electronic density of states tunneling inversion for A15 superconductors: Nb3Sn
We re-examine the tunneling data on A15 superconductors by performing a
generalized McMillan-Rowell tunneling inversion that incorporates a nonconstant
electronic density of states obtained from band-structure calculations. For
Nb3Sn, we find that the fit to the experimental data can be slightly improved
by taking into account the sharp structure in the density of states, but it is
likely that such an analysis alone is not enough to completely explain the
superconducting tunneling characteristics of this material. Nevertheless, the
extracted Eliashberg function displays a number of features expected to be
present for the highest quality Nb3Sn samples.Comment: 11 pages, 11 figure
The Fueling and Evolution of AGN: Internal and External Triggers
In this chapter, I review the fueling and evolution of active galactic nuclei
(AGN) under the influence of internal and external triggers, namely intrinsic
properties of host galaxies (morphological or Hubble type, color, presence of
bars and other non-axisymmetric features, etc) and external factors such as
environment and interactions. The most daunting challenge in fueling AGN is
arguably the angular momentum problem as even matter located at a radius of a
few hundred pc must lose more than 99.99 % of its specific angular momentum
before it is fit for consumption by a BH. I review mass accretion rates,
angular momentum requirements, the effectiveness of different fueling
mechanisms, and the growth and mass density of black BHs at different epochs. I
discuss connections between the nuclear and larger-scale properties of AGN,
both locally and at intermediate redshifts, outlining some recent results from
the GEMS and GOODS HST surveys.Comment: Invited Review Chapter to appear in LNP Volume on "AGN Physics on All
Scales", Chapter 6, in press. 40 pages, 12 figures. Typo in Eq 5 correcte
Star Formation and Dynamics in the Galactic Centre
The centre of our Galaxy is one of the most studied and yet enigmatic places
in the Universe. At a distance of about 8 kpc from our Sun, the Galactic centre
(GC) is the ideal environment to study the extreme processes that take place in
the vicinity of a supermassive black hole (SMBH). Despite the hostile
environment, several tens of early-type stars populate the central parsec of
our Galaxy. A fraction of them lie in a thin ring with mild eccentricity and
inner radius ~0.04 pc, while the S-stars, i.e. the ~30 stars closest to the
SMBH (<0.04 pc), have randomly oriented and highly eccentric orbits. The
formation of such early-type stars has been a puzzle for a long time: molecular
clouds should be tidally disrupted by the SMBH before they can fragment into
stars. We review the main scenarios proposed to explain the formation and the
dynamical evolution of the early-type stars in the GC. In particular, we
discuss the most popular in situ scenarios (accretion disc fragmentation and
molecular cloud disruption) and migration scenarios (star cluster inspiral and
Hills mechanism). We focus on the most pressing challenges that must be faced
to shed light on the process of star formation in the vicinity of a SMBH.Comment: 68 pages, 35 figures; invited review chapter, to be published in
expanded form in Haardt, F., Gorini, V., Moschella, U. and Treves, A.,
'Astrophysical Black Holes'. Lecture Notes in Physics. Springer 201
Association of gamma-glutamyltransferase levels with total mortality, liver-related, and cardiovascular outcomes: a prospective cohort study in the UK Biobank
Background:
Gamma-glutamyltransferase (GGT) levels in the blood can be a sensitive marker of liver injury but the extent to which they give insight into risk across multiple outcomes in a clinically useful way remains uncertain.
Methods:
Using data from 293,667 UK Biobank participants, the relationship of GGT concentrations to self-reported alcohol intake and adiposity markers were investigated. We next investigated whether GGT predicted liver-related, cardiovascular (CV) or all-cause mortality, and potentially improved CV risk prediction.
Findings:
Higher alcohol intake and greater waist circumference (WC) were associated with higher GGT; the association was stronger for alcohol with evidence of a synergistic effect of WC. Higher GGT concentrations were associated with multiple outcomes. Compared to a GGT of 14.5 U/L (lowest decile), values of 48 U/L for women and 60 U/L for men (common upper limits of ‘normal’) had hazard ratios (HRs) for liver-related mortality of 1.83 (95% CI 1.60–2.11) and 3.25 (95% CI 2.38–4.42) respectively, for CV mortality of 1.21 (95% CI 1.14–1.28) and 1.43 (95% CI 1.27–1.60) and for all-cause mortality of 1.15 (95% CI 1.12–1.18) and 1.31 (95% CI 1.24–1.38). Adding GGT to a risk algorithm for CV mortality reclassified an additional 1.24% (95% CI 0.14–2.34) of participants across a binary 5% 10-year risk threshold.
Interpretation:
Our study suggests that a modest elevation in GGT levels should trigger a discussion with the individual to review diet and lifestyle including alcohol intake and consideration of formal liver disease and CV risk assessment if not previously done.
Funding:
British Heart Foundation Centre of Research Excellence Grant (grant number RE/18/6/34217), NHS Research Scotland (grant number SCAF/15/02), the Medical Research Council (grant number MC_UU_00022/2); and the Scottish Government Chief Scientist Office (grant number SPHSU17)
Stochastic Acceleration by Turbulence
The subject of this paper is stochastic acceleration by plasma turbulence, a
process akin to the original model proposed by Fermi. We review the relative
merits of different acceleration models, in particular the so called first
order Fermi acceleration by shocks and second order Fermi by stochastic
processes, and point out that plasma waves or turbulence play an important role
in all mechanisms of acceleration. Thus, stochastic acceleration by turbulence
is active in most situations. We also show that it is the most efficient
mechanism of acceleration of relatively cool non relativistic thermal
background plasma particles. In addition, it can preferentially accelerate
electrons relative to protons as is needed in many astrophysical radiating
sources, where usually there are no indications of presence of shocks. We also
point out that a hybrid acceleration mechanism consisting of initial
acceleration by turbulence of background particles followed by a second stage
acceleration by a shock has many attractive features. It is demonstrated that
the above scenarios can account for many signatures of the accelerated
electrons, protons and other ions, in particular He and He, seen
directly as Solar Energetic Particles and through the radiation they produce in
solar flares.Comment: 29 pages 7 figures for proceedings of ISSI-Bern workshop on Particle
Acceleration 201
- …