1,404 research outputs found
Metric projective geometry, BGG detour complexes and partially massless gauge theories
A projective geometry is an equivalence class of torsion free connections
sharing the same unparametrised geodesics; this is a basic structure for
understanding physical systems. Metric projective geometry is concerned with
the interaction of projective and pseudo-Riemannian geometry. We show that the
BGG machinery of projective geometry combines with structures known as
Yang-Mills detour complexes to produce a general tool for generating invariant
pseudo-Riemannian gauge theories. This produces (detour) complexes of
differential operators corresponding to gauge invariances and dynamics. We
show, as an application, that curved versions of these sequences give geometric
characterizations of the obstructions to propagation of higher spins in
Einstein spaces. Further, we show that projective BGG detour complexes generate
both gauge invariances and gauge invariant constraint systems for partially
massless models: the input for this machinery is a projectively invariant gauge
operator corresponding to the first operator of a certain BGG sequence. We also
connect this technology to the log-radial reduction method and extend the
latter to Einstein backgrounds.Comment: 30 pages, LaTe
Quantum Gravity and Causal Structures: Second Quantization of Conformal Dirac Algebras
It is postulated that quantum gravity is a sum over causal structures coupled
to matter via scale evolution. Quantized causal structures can be described by
studying simple matrix models where matrices are replaced by an algebra of
quantum mechanical observables. In particular, previous studies constructed
quantum gravity models by quantizing the moduli of Laplace, weight and
defining-function operators on Fefferman-Graham ambient spaces. The algebra of
these operators underlies conformal geometries. We extend those results to
include fermions by taking an osp(1|2) "Dirac square root" of these algebras.
The theory is a simple, Grassmann, two-matrix model. Its quantum action is a
Chern-Simons theory whose differential is a first-quantized, quantum mechanical
BRST operator. The theory is a basic ingredient for building fundamental
theories of physical observables.Comment: 4 pages, LaTe
Charge dynamics in molecular junctions: Nonequilibrium Green's Function approach made fast
Real-time Green's function simulations of molecular junctions (open quantum
systems) are typically performed by solving the Kadanoff-Baym equations (KBE).
The KBE, however, impose a serious limitation on the maximum propagation time
due to the large memory storage needed. In this work we propose a simplified
Green's function approach based on the Generalized Kadanoff-Baym Ansatz (GKBA)
to overcome the KBE limitation on time, significantly speed up the
calculations, and yet stay close to the KBE results. This is achieved through a
twofold advance: first we show how to make the GKBA work in open systems and
then construct a suitable quasi-particle propagator that includes correlation
effects in a diagrammatic fashion. We also provide evidence that our GKBA
scheme, although already in good agreement with the KBE approach, can be
further improved without increasing the computational cost.Comment: 13 pages, 13 figure
Quantum Principal Bundles on Projective Bases
The purpose of this paper is to propose a sheaf theoretic approach to the theory of quantum principal bundles over non affine bases. We study noncommutative principal bundles corresponding to G→ G/ P, where G is a semisimple group and P a parabolic subgroup
The -linked complex Minkowski space, its real forms and deformed isometry groups
We establish duality between real forms of the quantum deformation of the
4-dimensional orthogonal group studied by Fioresi et al. and the classification
work made by Borowiec et al.. Classically these real forms are the isometry
groups of equipped with Euclidean, Kleinian or Lorentzian
metric. A general deformation, named -linked, of each of these spaces is
then constructed, together with the coaction of the corresponding isometry
group.Comment: 25 pages, discussion improved, bibliography update
New insight into WDVV equation
We show that Witten-Dijkgraaf-Verlinde-Verlinde equation underlies the
construction of N=4 superconformal multi--particle mechanics in one dimension,
including a N=4 superconformal Calogero model.Comment: 16 pages, no figures, LaTeX file, PACS: 04.60.Ds; 11.30.P
The symplectic origin of conformal and Minkowski superspaces
Supermanifolds provide a very natural ground to understand and handle
supersymmetry from a geometric point of view; supersymmetry in and
dimensions is also deeply related to the normed division algebras.
In this paper we want to show the link between the conformal group and
certain types of symplectic transformations over division algebras. Inspired by
this observation we then propose a new\,realization of the real form of the 4
dimensional conformal and Minkowski superspaces we obtain, respectively, as a
Lagrangian supermanifold over the twistor superspace and a
big cell inside it.
The beauty of this approach is that it naturally generalizes to the 6
dimensional case (and possibly also to the 10 dimensional one) thus providing
an elegant and uniform characterization of the conformal superspaces.Comment: 15 pages, references added, minor change
Aldosterone status associates with insulin resistance in patients with heart failure-data from the ALOFT study
<b>Background</b>: Aldosterone plays a key role in the pathophysiology of heart failure. In around 50% of such patients, aldosterone 'escapes' from inhibition by drugs that interrupt the renin-angiotensin axis; such patients have a worse clinical outcome. Insulin resistance is a risk factor in heart failure and cardiovascular disease. The relationship between aldosterone status and insulin sensitivity was investigated in a cohort of heart failure patients.
<b>Methods</b>: 302 patients with New York Heart Association (NYHA) class II-IV heart failure on conventional therapy were randomized in ALiskiren Observation of heart Failure Treatment study (ALOFT), designed to test the safety of a directly acting renin inhibitor. Plasma aldosterone and 24-hour urinary aldosterone excretion as well as fasting insulin and Homeostasis model assessment of insulin resistance (HOMA-IR) were measured. Subjects with aldosterone escape and high urinary aldosterone were identified according to previously accepted definitions.
<b>Results</b>: Twenty per-cent of subjects demonstrated aldosterone escape and 34% had high urinary aldosterone levels. At baseline, there was a positive correlation between fasting insulin and plasma(r=0.22 p<0.01) and urinary aldosterone(r=0.19 p<0.03). Aldosterone escape and high urinary aldosterone subjects both demonstrated higher levels of fasting insulin (p<0.008, p<0.03), HOMA-IR (p<0.06, p<0.03) and insulin-glucose ratios (p<0.006, p<0.06) when compared to low aldosterone counterparts. All associations remained significant when adjusted for potential confounders.
<b>Conclusions</b>: This study demonstrates a novel direct relationship between aldosterone status and insulin resistance in heart failure. This observation merits further study and may identify an additional mechanism that contributes to the adverse clinical outcome associated with aldosterone escape
Analysis of enhanced diffusion in Taylor dispersion via a model problem
We consider a simple model of the evolution of the concentration of a tracer,
subject to a background shear flow by a fluid with viscosity in an
infinite channel. Taylor observed in the 1950's that, in such a setting, the
tracer diffuses at a rate proportional to , rather than the expected
rate proportional to . We provide a mathematical explanation for this
enhanced diffusion using a combination of Fourier analysis and center manifold
theory. More precisely, we show that, while the high modes of the concentration
decay exponentially, the low modes decay algebraically, but at an enhanced
rate. Moreover, the behavior of the low modes is governed by finite-dimensional
dynamics on an appropriate center manifold, which corresponds exactly to
diffusion by a fluid with viscosity proportional to
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