89 research outputs found
An assessment of Evans' unified field theory II
Evans developed a classical unified field theory of gravitation and
electromagnetism on the background of a spacetime obeying a Riemann-Cartan
geometry. In an accompanying paper I, we analyzed this theory and summarized it
in nine equations. We now propose a variational principle for Evans' theory and
show that it yields two field equations. The second field equation is algebraic
in the torsion and we can resolve it with respect to the torsion. It turns out
that for all physical cases the torsion vanishes and the first field equation,
together with Evans' unified field theory, collapses to an ordinary Einstein
equation.Comment: 11 pages of late
An assessment of Evans' unified field theory I
Evans developed a classical unified field theory of gravitation and
electromagnetism on the background of a spacetime obeying a Riemann-Cartan
geometry. This geometry can be characterized by an orthonormal coframe theta
and a (metric compatible) Lorentz connection Gamma. These two potentials yield
the field strengths torsion T and curvature R. Evans tried to infuse
electromagnetic properties into this geometrical framework by putting the
coframe theta to be proportional to four extended electromagnetic potentials A;
these are assumed to encompass the conventional Maxwellian potential in a
suitable limit. The viable Einstein-Cartan(-Sciama-Kibble) theory of gravity
was adopted by Evans to describe the gravitational sector of his theory.
Including also the results of an accompanying paper by Obukhov and the author,
we show that Evans' ansatz for electromagnetism is untenable beyond repair both
from a geometrical as well as from a physical point of view. As a consequence,
his unified theory is obsolete.Comment: 39 pages of latex, modified because of referee report, mistakes and
typos removed, partly reformulated, taken care of M.W.Evans' rebutta
Maxwell's field coupled nonminimally to quadratic torsion: Induced axion field and birefringence of the vacuum
We consider a possible (parity conserving) interaction between the
electromagnetic field and a torsion field of spacetime. For
generic elementary torsion, gauge invariant coupling terms of lowest order fall
into two classes that are both nonminimal and {\it quadratic} in torsion. These
two classes are displayed explicitly. The first class of the type
yields (undesirable) modifications of the Maxwell equations. The second class
of the type doesn't touch the Maxwell equations but rather
modifies the constitutive tensor of spacetime. Such a modification can be
completely described in the framework of metricfree electrodynamics. We
recognize three physical effects generated by the torsion: (i) An axion field
that induces an {\em optical activity} into spacetime, (ii) a modification of
the light cone structure that yields {\em birefringence} of the vacuum, and
(iii) a torsion dependence of the {\em velocity of light.} We study these
effects in the background of a Friedmann universe with torsion. {\it File
tor17.tex, 02 August 2003}Comment: 6 page
Cartan's spiral staircase in physics and, in particular, in the gauge theory of dislocations
In 1922, Cartan introduced in differential geometry, besides the Riemannian
curvature, the new concept of torsion. He visualized a homogeneous and
isotropic distribution of torsion in three dimensions (3d) by the "helical
staircase", which he constructed by starting from a 3d Euclidean space and by
defining a new connection via helical motions. We describe this geometric
procedure in detail and define the corresponding connection and the torsion.
The interdisciplinary nature of this subject is already evident from Cartan's
discussion, since he argued - but never proved - that the helical staircase
should correspond to a continuum with constant pressure and constant internal
torque. We discuss where in physics the helical staircase is realized: (i) In
the continuum mechanics of Cosserat media, (ii) in (fairly speculative) 3d
theories of gravity, namely a) in 3d Einstein-Cartan gravity - this is Cartan's
case of constant pressure and constant intrinsic torque - and b) in 3d Poincare
gauge theory with the Mielke-Baekler Lagrangian, and, eventually, (iii) in the
gauge field theory of dislocations of Lazar et al., as we prove for the first
time by arranging a suitable distribution of screw dislocations. Our main
emphasis is on the discussion of dislocation field theory.Comment: 31 pages, 8 figure
Avoiding degenerate coframes in an affine gauge approach to quantum gravity
In quantum models of gravity, it is surmized that configurations with
degenerate coframes could occur during topology change of the underlying
spacetime structure. However, the coframe is not the true Yang--Mills type
gauge field of the translations, since it lacks the inhomogeneous gradient term
in the gauge transformations. By explicitly restoring this ``hidden" piece
within the framework of the affine gauge approach to gravity, one can avoid the
metric or coframe degeneracy which would otherwise interfere with the
integrations within the path integral. This is an important advantage for
quantization.Comment: 14 pages, Preprint Cologne-thp-1993-H
Prognostic implications of coronary calcification in patients with obstructive coronary artery disease treated by percutaneous coronary intervention: A patient-level pooled analysis of 7 contemporary stent trials
Objective To investigate the long- Term prognostic implications of coronary calcification in patients undergoing percutaneous coronary intervention for obstructive coronary artery disease. Methods Patient-level data from 6296 patients enrolled in seven clinical drug-eluting stents trials were analysed to identify in angiographic images the presence of severe coronary calcification by an independent academic research organisation (Cardialysis, Rotterdam, The Netherlands). Clinical outcomes at 3-years follow-up including all-cause mortality, death-myocardial infarction (MI), and the composite end-point of all-cause death-MI- Any revascularisation were compared between patients with and without severe calcification. Results Severe calcification was detected in 20% of the studied population. Patients with severe lesion calcification were less likely to have undergone complete revascularisation (48% vs 55.6%, p<0.001) and had an increased mortality compared with those without severely calcified arteries (10.8% vs 4.4%, p<0.001). The event rate was also high in patients with severely calcified lesions for the combined end-point death-MI (22.9% vs 10.9%; p<0.001) and death-MI- Any revascularisation (31.8% vs 22.4%; p<0.001). On multivariate Cox regression analysis, including the Syntax score, the presence of severe coronary calcification was an independent predictor of poor prognosis (HR: 1.33 95% CI 1.00 to 1.77, p=0.047 for death; 1.23, 95% CI 1.02 to 1.49, p=0.031 for death-MI, and 1.18, 95% CI 1.01 to 1.39, p=0.042 for death-MI- Any revascularisation), but it was not associated with an increased risk of stent thrombosis. Conclusions Patients with severely calcified lesions have worse clinical outcomes compared to those without severe coronary calcification. Severe coronary calcification appears as an independent predictor of worse prognosis, and should be considered as a marker of advanced atherosclerosis
Economic outcomes of percutaneous coronary intervention with drug-eluting stents versus bypass surgery for patients with left main or three-vessel coronary artery disease: One-year results from the SYNTAX trial
Objectives: To evaluate the cost-effectiveness of alternative approaches to revascularization for patients with three-vessel or left main coronary artery disease (CAD). Background: Previous studies have demonstrated that, despite higher initial costs, long-term costs with bypass surgery (CABG) in multivessel CAD are similar to those for percutaneous coronary intervention (PCI). The impact of drug-eluting stents (DES) on these results is unknown. Methods: The SYNTAX trial randomized 1,800 patients with left main or three-vessel CAD to either CABG (n = 897) or PCI using paclitaxel-eluting stents (n = 903). Resource utilization data were collected prospectively for all patients, and cumulative 1-year costs were assessed from the perspective of the U.S. healthcare system. Results: Total costs for the initial hospitalization were 2,282/patient higher with PCI due mainly to more frequent revascularization procedures and higher outpatient medication costs. Total 1-year costs were thus 43,486 per quality-adjusted life-year gained. Conclusions: Among patients with three-vessel or left main CAD, PCI is an economically attractive strategy over the first year for patients with low and moderate angiographic complexity, while CABG is favored among patients with high angiographic complexity
The unexpected resurgence of Weyl geometry in late 20-th century physics
Weyl's original scale geometry of 1918 ("purely infinitesimal geometry") was
withdrawn by its author from physical theorizing in the early 1920s. It had a
comeback in the last third of the 20th century in different contexts: scalar
tensor theories of gravity, foundations of gravity, foundations of quantum
mechanics, elementary particle physics, and cosmology. It seems that Weyl
geometry continues to offer an open research potential for the foundations of
physics even after the turn to the new millennium.Comment: Completely rewritten conference paper 'Beyond Einstein', Mainz Sep
2008. Preprint ELHC (Epistemology of the LHC) 2017-02, 92 pages, 1 figur
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