351 research outputs found
Dynamics of false vacuum bubbles: beyond the thin shell approximation
We numerically study the dynamics of false vacuum bubbles which are inside an
almost flat background; we assumed spherical symmetry and the size of the
bubble is smaller than the size of the background horizon. According to the
thin shell approximation and the null energy condition, if the bubble is
outside of a Schwarzschild black hole, unless we assume Farhi-Guth-Guven
tunneling, expanding and inflating solutions are impossible. In this paper, we
extend our method to beyond the thin shell approximation: we include the
dynamics of fields and assume that the transition layer between a true vacuum
and a false vacuum has non-zero thickness. If a shell has sufficiently low
energy, as expected from the thin shell approximation, it collapses (Type 1).
However, if the shell has sufficiently large energy, it tends to expand. Here,
via the field dynamics, field values of inside of the shell slowly roll down to
the true vacuum and hence the shell does not inflate (Type 2). If we add
sufficient exotic matters to regularize the curvature near the shell, inflation
may be possible without assuming Farhi-Guth-Guven tunneling. In this case, a
wormhole is dynamically generated around the shell (Type 3). By tuning our
simulation parameters, we could find transitions between Type 1 and Type 2, as
well as between Type 2 and Type 3. Between Type 2 and Type 3, we could find
another class of solutions (Type 4). Finally, we discuss the generation of a
bubble universe and the violation of unitarity. We conclude that the existence
of a certain combination of exotic matter fields violates unitarity.Comment: 40 pages, 41 figure
Off-shell superconformal nonlinear sigma-models in three dimensions
We develop superspace techniques to construct general off-shell N=1,2,3,4
superconformal sigma-models in three space-time dimensions. The most general
N=3 and N=4 superconformal sigma-models are constructed in terms of N=2 chiral
superfields. Several superspace proofs of the folklore statement that N=3
supersymmetry implies N=4 are presented both in the on-shell and off-shell
settings. We also elaborate on (super)twistor realisations for (super)manifolds
on which the three-dimensional N-extended superconformal groups act
transitively and which include Minkowski space as a subspace.Comment: 67 pages; V2: typos corrected, one reference added, version to appear
on JHE
The no-boundary measure in scalar-tensor gravity
In this article, we study the no-boundary wave function in scalar-tensor
gravity with various potentials for the non-minimally coupled scalar field. Our
goal is to calculate probabilities for the scalar field - and hence the
effective gravitational coupling and cosmological constant - to take specific
values. Most calculations are done in the minisuperspace approximation, and we
use a saddle point approximation for the Euclidean action, which is then
evaluated numerically. We find that for potentials that have several minima,
none of them is substantially preferred by the quantum mechanical
probabilities. We argue that the same is true for the stable and the runaway
solution in the case of a dilaton-type potential. Technically, this is due to
the inclusion of quantum mechanical effects (fuzzy instantons). These results
are in contrast to the often held view that vanishing gravitation or
cosmological constants would be exponentially preferred in quantum cosmology,
and they may be relevant to the cosmological constant problem and the dilaton
stabilization problem.Comment: 31 pages, 9 figure
N = 2 supersymmetric sigma-models and duality
For two families of four-dimensional off-shell N = 2 supersymmetric nonlinear
sigma-models constructed originally in projective superspace, we develop their
formulation in terms of N = 1 chiral superfields. Specifically, these theories
are: (i) sigma-models on cotangent bundles T*M of arbitrary real analytic
Kaehler manifolds M; (ii) general superconformal sigma-models described by
weight-one polar supermultiplets. Using superspace techniques, we obtain a
universal expression for the holomorphic symplectic two-form \omega^{(2,0)}
which determines the second supersymmetry transformation and is associated with
the two complex structures of the hyperkaehler space T*M that are complimentary
to the one induced from M. This two-form is shown to coincide with the
canonical holomorphic symplectic structure. In the case (ii), we demonstrate
that \omega^{(2,0)} and the homothetic conformal Killing vector determine the
explicit form of the superconformal transformations. At the heart of our
construction is the duality (generalized Legendre transform) between off-shell
N = 2 supersymmetric nonlinear sigma-models and their on-shell N = 1 chiral
realizations. We finally present the most general N = 2 superconformal
nonlinear sigma-model formulated in terms of N = 1 chiral superfields. The
approach developed can naturally be generalized in order to describe 5D and 6D
superconformal nonlinear sigma-models in 4D N = 1 superspace.Comment: 31 pages, no figures; V2: reference and comments added, typos
corrected; V3: more typos corrected, published versio
Spinal Cord Stimulation for Refractory Angina Pectoris -A Case Report-
Refractory angina pectoris is defined as angina refractory to optimal medical treatment and standard coronary revascularization procedures. Despite recent therapeutic advances, patients with refractory angina pectoris are not adequately treated. Spinal cord stimulation is a minimally invasive and reversible technique which utilizes electrical neuromodulation by means of an electrode implanted in the epidural space. It has been reported to be an effective and safe treatment for refractory angina pectoris. We report a case of spinal cord stimulation which has effectively relieved chest pain due to coronary artery disease in a 40-year-old man. This is the first report of spinal cord stimulation for treatment of refractory angina pectoris in South Korea
Three-dimensional (p,q) AdS superspaces and matter couplings
We introduce N-extended (p,q) AdS superspaces in three space-time dimensions,
with p+q=N and p>=q, and analyse their geometry. We show that all (p,q) AdS
superspaces with X^{IJKL}=0 are conformally flat. Nonlinear sigma-models with
(p,q) AdS supersymmetry exist for p+q4 the target space geometries
are highly restricted). Here we concentrate on studying off-shell N=3
supersymmetric sigma-models in AdS_3. For each of the cases (3,0) and (2,1), we
give three different realisations of the supersymmetric action. We show that
(3,0) AdS supersymmetry requires the sigma-model to be superconformal, and
hence the corresponding target space is a hyperkahler cone. In the case of
(2,1) AdS supersymmetry, the sigma-model target space must be a non-compact
hyperkahler manifold endowed with a Killing vector field which generates an
SO(2) group of rotations of the two-sphere of complex structures.Comment: 52 pages; V3: minor corrections, version published in JHE
Off-shell supergravity-matter couplings in three dimensions
We develop the superspace geometry of N-extended conformal supergravity in
three space-time dimensions. General off-shell supergravity-matter couplings
are constructed in the cases N=1,2,3,4.Comment: 73 pages; V5: typos in eqs. (3.4b), (3.17) and (4.24) correcte
Developing the islamic financial services sector in Italy: An institutional theory perspective
© The Editor(s) (if applicable) and the Author(s) 2016. The Islamic Financial Services (IFS) sector has experienced wider consumer acceptance and rapid growth since its commercial launch in the 1970s. This growth has primarily been in countries in Asia such as Iran, Malaysia, Pakistan and the Middle East region. Although non-Muslim majority countries like Hong Kong and Singapore have taken positive strides in developing the sector, European countries have lagged behind their Asian counterparts (Daily Times, 2013). Europe is host to a large Muslim population, but the lack of developed Islamic financial institutions means that the potential of IFS product offerings is yet to be fully realized in the region (Volk and Pudelko, 2010)
Rationale and design of a randomised controlled trial evaluating the effectiveness of an exercise program to improve the quality of life of patients with heart failure in primary care : the EFICAR study protocol
Background: Quality of life (QoL) decreases as heart failure worsens, which is one of the greatest worries of these patients. Physical exercise has been shown to be safe for people with heart failure. Previous studies have tested heterogeneous exercise programs using different QoL instruments and reported inconsistent effects on QoL. The aim of this study is to evaluate the effectiveness of a new exercise program for people with heart failure (EFICAR), additional to the recommended optimal treatment in primary care, to improve QoL, functional capacity and control of cardiovascular risk factors. Methods/Design: Multicenter clinical trial in which 600 patients with heart failure in NYHA class II-IV will be randomized to two parallel groups: EFICAR and control. After being recruited, through the reference cardiology services, in six health centres from the Spanish Primary Care Prevention and Health Promotion Research Network (redIAPP), patients are followed for 1 year after the beginning of the intervention. Both groups receive the optimized treatment according to the European Society of Cardiology guidelines. In addition, the EFICAR group performs a 3 month supervised progressive exercise program with an aerobic (high-intensity intervals) and a strength component; and the programme continues linked with community resources for 9 months. The main outcome measure is the change in health-related QoL measured by the SF-36 and the Minnesota Living with Heart Failure Questionnaires at baseline, 3, 6 and 12 months. Secondary outcomes considered are changes in functional capacity measured by the 6-Minute Walking Test, cardiac structure (B-type natriuretic peptides), muscle strength and body composition. Both groups will be compared on an intention to treat basis, using multi-level longitudinal mixed models. Sex, age, social class, co-morbidity and cardiovascular risk factors will be considered as potential confounding and predictor variables. Discussion: A key challenges of this study is to guarantee the safety of the patients; however, the current scientific evidence supports the notion of there being no increase in the risk of decompensation, cardiac events, hospitalizations and deaths associated with exercise, but rather the opposite. Safety assurance will be based on an optimized standardised pharmacological therapy and health education for all the participants
Economic and biological costs of cardiac imaging
Medical imaging market consists of several billion tests per year worldwide. Out of these, at least one third are cardiovascular procedures. Keeping in mind that each test represents a cost, often a risk, and a diagnostic hypothesis, we can agree that every unnecessary and unjustifiable test is one test too many. Small individual costs, risks, and wastes multiplied by billions of examinations per year represent an important population, society and environmental burden. Unfortunately, the appropriateness of cardiac imaging is extra-ordinarily low and there is little awareness in patients and physicians of differential costs, radiological doses, and long term risks of different imaging modalities. For a resting cardiac imaging test, being the average cost (not charges) of an echocardiogram equal to 1 (as a cost comparator), the cost of a CT is 3.1x, of a SPECT 3.27x, of a Cardiovascular Magnetic Resonance imaging 5.51x, of a PET 14.03x, and of a right and left heart catheterization 19.96x. For stress cardiac imaging, compared with the treadmill exercise test equal to 1 (as a cost comparator), the cost of stress echocardiography is 2.1x and of a stress SPECT scintigraphy is 5.7x. Biohazards and downstream long-term costs linked to radiation-induced oncogenesis should also be considered. The radiation exposure is absent in echo and magnetic resonance, and corresponds to 500 chest x rays for a sestamibi cardiac stress scan and to 1150 chest x rays for a thallium scan. The corresponding extra-risk in a lifetime of fatal cancer is 1 in 2000 exposed patients for a sestamibi stress and 1 in 1000 for a thallium scan. Increased awareness of economic, biologic, and environmental costs of cardiac imaging will hopefully lead to greater appropriateness, wisdom and prudence from both the prescriber and the practitioner. In this way, the sustainability of cardiac imaging will eventually improve
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