117 research outputs found
Superfluid vs Ferromagnetic Behaviour in a Bose Gas of Spin-1/2 Atoms
We study the thermodynamic phases of a gas of spin-1/2 atoms in the
Hartree-Fock approximation. Our main result is that, for repulsive or
weakly-attractive inter-component interaction strength, the superfluid and
ferromagnetic phase transitions occur at the same temperature. For
strongly-attractive inter-component interaction strength, however, the
ferromagnetic phase transition occurs at a higher temperature than the
superfluid phase transition. We also find that the presence of a condensate
acts as an effective magnetic field that polarizes the normal cloud. We finally
comment on the validity of the Hartree-Fock approximation in describing
different phenomena in this system.Comment: 10 pages, 2 figure
Holographic realization of gauge mediated supersymmetry breaking
The general gauge mediation scenario provides a framework in which properties
of a visible sector with soft supersymmetry breaking are computed from current
correlation functions in the supersymmetry breaking hidden sector. In this
paper we will use holography to model strongly coupled hidden sectors by weakly
curved geometries and describe how the current correlators relevant for general
gauge mediation are computed by holographic methods. We illustrate the general
setup by a toy example which captures most of the relevant features.Comment: 11 pages, v2: comments and refs added, JHEP versio
Soft branes in supersymmetry-breaking backgrounds
We revisit the analysis of effective field theories resulting from
non-supersymmetric perturbations to supersymmetric flux compactifications of
the type-IIB superstring with an eye towards those resulting from the
backreaction of a small number of anti-D3-branes. Independently of the
background, we show that the low-energy Lagrangian describing the fluctuations
of a stack of probe D3-branes exhibits soft supersymmetry breaking, despite
perturbations to marginal operators that were not fully considered in some
previous treatments. We take this as an indication that the breaking of
supersymmetry by anti-D3-branes or other sources may be spontaneous rather than
explicit. In support of this, we consider the action of an anti-D3-brane
probing an otherwise supersymmetric configuration and identify a candidate for
the corresponding goldstino.Comment: 36+5 pages. References added, minor typos correcte
Electroweak Constraints on Warped Geometry in Five Dimensions and Beyond
Here we consider the tree level corrections to electroweak (EW) observables
from standard model (SM) particles propagating in generic warped extra
dimensions. The scale of these corrections is found to be dominated by three
parameters, the Kaluza-Klein (KK) mass scale, the relative coupling of the KK
gauge fields to the Higgs and the relative coupling of the KK gauge fields to
fermion zero modes. It is found that 5D spaces that resolve the hierarchy
problem through warping typically have large gauge-Higgs coupling. It is also
found in where the additional dimensions are warped the relative
gauge-Higgs coupling scales as a function of the warp factor. If the warp
factor of the additional spaces is contracting towards the IR brane, both the
relative gauge-Higgs coupling and resulting EW corrections will be large.
Conversely EW constraints could be reduced by finding a space where the
additional dimension's warp factor is increasing towards the IR brane. We
demonstrate that the Klebanov Strassler solution belongs to the former of these
possibilities.Comment: 18 pages, 3 figures (references added) version to appear in JHE
The Non-SUSY Baryonic Branch: Soft Supersymmetry Breaking of N=1 Gauge Theories
We study a non-supersymmetric deformation of the field theory dual to the
baryonic branch of Klebanov-Strassler. Using a combination of analytical
(series expansions) and numerical methods we construct non-supersymmetric
backgrounds that smoothly interpolate between the desired UV and IR behaviors.
We calculate various observables of the field theory and propose a picture of
soft breaking by gaugino masses that is consistent with the various
calculations on the string side.Comment: 32 pages plus many appendixes. One figur
IMPLEmenting a clinical practice guideline for acute low back pain evidence-based manageMENT in general practice (IMPLEMENT) : cluster randomised controlled trial study protocol
Background: Evidence generated from reliable research is not frequently implemented into clinical practice. Evidence-based clinical practice guidelines are a potential vehicle to achieve this. A recent systematic review of implementation strategies of guideline dissemination concluded that there was a lack of evidence regarding effective strategies to promote the uptake of guidelines. Recommendations from this review, and other studies, have suggested the use of interventions that are theoretically based because these may be more effective than those that are not. An evidencebased clinical practice guideline for the management of acute low back pain was recently developed in Australia. This provides an opportunity to develop and test a theory-based implementation intervention for a condition which is common, has a high burden, and for which there is an evidence-practice gap in the primary care setting. Aim: This study aims to test the effectiveness of a theory-based intervention for implementing a clinical practice guideline for acute low back pain in general practice in Victoria, Australia. Specifically, our primary objectives are to establish if the intervention is effective in reducing the percentage of patients who are referred for a plain x-ray, and improving mean level of disability for patients three months post-consultation. Methods/Design: This study protocol describes the details of a cluster randomised controlled trial. Ninety-two general practices (clusters), which include at least one consenting general practitioner, will be randomised to an intervention or control arm using restricted randomisation. Patients aged 18 years or older who visit a participating practitioner for acute non-specific low back pain of less than three months duration will be eligible for inclusion. An average of twenty-five patients per general practice will be recruited, providing a total of 2,300 patient participants. General practitioners in the control arm will receive access to the guideline using the existing dissemination strategy. Practitioners in the intervention arm will be invited to participate in facilitated face-to-face workshops that have been underpinned by behavioural theory. Investigators (not involved in the delivery of the intervention), patients, outcome assessors and the study statistician will be blinded to group allocation. Trial registration: Australian New Zealand Clinical Trials Registry ACTRN012606000098538 (date registered 14/03/2006).The trial is funded by the NHMRC by way of a Primary Health Care Project Grant (334060). JF has 50% of her time funded by the Chief Scientist Office3/2006). of the Scottish Government Health Directorate and 50% by the University of Aberdeen. PK is supported by a NHMRC Health Professional Fellowship (384366) and RB by a NHMRC Practitioner Fellowship (334010). JG holds a Canada Research Chair in Health Knowledge Transfer and Uptake. All other authors are funded by their own institutions
Precision Measurement of the Newtonian Gravitational Constant Using Cold Atoms
About 300 experiments have tried to determine the value of the Newtonian
gravitational constant, G, so far, but large discrepancies in the results have
made it impossible to know its value precisely. The weakness of the
gravitational interaction and the impossibility of shielding the effects of
gravity make it very difficult to measure G while keeping systematic effects
under control. Most previous experiments performed were based on the torsion
pendulum or torsion balance scheme as in the experiment by Cavendish in 1798,
and in all cases macroscopic masses were used. Here we report the precise
determination of G using laser-cooled atoms and quantum interferometry. We
obtain the value G=6.67191(99) x 10^(-11) m^3 kg^(-1) s^(-2) with a relative
uncertainty of 150 parts per million (the combined standard uncertainty is
given in parentheses). Our value differs by 1.5 combined standard deviations
from the current recommended value of the Committee on Data for Science and
Technology. A conceptually different experiment such as ours helps to identify
the systematic errors that have proved elusive in previous experiments, thus
improving the confidence in the value of G. There is no definitive relationship
between G and the other fundamental constants, and there is no theoretical
prediction for its value, against which to test experimental results. Improving
the precision with which we know G has not only a pure metrological interest,
but is also important because of the key role that G has in theories of
gravitation, cosmology, particle physics and astrophysics and in geophysical
models.Comment: 3 figures, 1 tabl
Holographic Correlators for General Gauge Mediation
We use holographic techniques to compute two-point functions of operators
belonging to a conserved current supermultiplet in theories which break
supersymmetry at strong coupling. These are the relevant quantities one has to
compute in models of gauge mediation to determine the soft spectrum in
supersymmetric extensions of the Standard Model (SSM). Such holographic
approach can be used for diverse gravitational backgrounds, but here we focus,
for definiteness, on asymptotically AdS backgrounds. After presenting the
general framework, we apply our formulas to two explicit examples which differ
by the nature of the SSM gauginos, which have Dirac or Majorana masses,
corresponding to models that respectively preserve or break R-symmetry.Comment: 30 pages, 6 figures. v3: clarifications added, typos corrected, refs
added, one figure improve
A slice of AdS_5 as the large N limit of Seiberg duality
A slice of AdS_5 is used to provide a 5D gravitational description of 4D
strongly-coupled Seiberg dual gauge theories. An (electric) SU(N) gauge theory
in the conformal window at large N is described by the 5D bulk, while its
weakly coupled (magnetic) dual is confined to the IR brane. This framework can
be used to construct an N = 1 MSSM on the IR brane, reminiscent of the original
Randall-Sundrum model. In addition, we use our framework to study
strongly-coupled scenarios of supersymmetry breaking mediated by gauge forces.
This leads to a unified scenario that connects the extra-ordinary gauge
mediation limit to the gaugino mediation limit in warped space.Comment: 47 Pages, axodraw4j.st
Detecting inertial effects with airborne matter-wave interferometry
Inertial sensors relying on atom interferometry offer a breakthrough advance
in a variety of applications, such as inertial navigation, gravimetry or
ground- and space-based tests of fundamental physics. These instruments require
a quiet environment to reach their performance and using them outside the
laboratory remains a challenge. Here we report the first operation of an
airborne matter-wave accelerometer set up aboard a 0g plane and operating
during the standard gravity (1g) and microgravity (0g) phases of the flight. At
1g, the sensor can detect inertial effects more than 300 times weaker than the
typical acceleration fluctuations of the aircraft. We describe the improvement
of the interferometer sensitivity in 0g, which reaches 2 x 10-4 ms-2 / \surdHz
with our current setup. We finally discuss the extension of our method to
airborne and spaceborne tests of the Universality of free fall with matter
waves.Comment: 7 pages, 6 figures. The final version of this article is available in
OPEN access (free) from the editor website at
http://www.nature.com/ncomms/journal/v2/n9/full/ncomms1479.htm
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