53,116 research outputs found
Vacuum tunneling in gravity
Topologically non-trivial vacuum structure in gravity models with Cartan
variables (vielbein and contortion) is considered. We study the possibility of
vacuum space-time tunneling in Einstein gravity assuming that the vielbein may
play a fundamental role in quantum gravitational phenomena. It has been shown
that in the case of RP3 space topology the tunneling between non-trivial
topological vacuums can be realized by means of Eguchi-Hanson gravitational
instanton. In Riemann-Cartan geometric approach to quantum gravity the vacuum
tunneling can be provided by means of contortion quantum fluctuations. We
define double self-duality condition for the contortion and give explicit
self-dual configurations which can contribute to vacuum tunneling amplitude.Comment: 11 pages, 1 fig. is added, final versio
Cho and Pak reply to Lamm et al. comment on "A Convergent Series for the QED Effective Action"
Cho and Pak reply to Lamm et al. [hep-th/0007108] comment on "A Convergent
Series for the Effective Action of QED" [hep-th/0006057].Comment: 1 pag
Perturbation and scaled Cook's distance
Cook's distance [Technometrics 19 (1977) 15-18] is one of the most important
diagnostic tools for detecting influential individual or subsets of
observations in linear regression for cross-sectional data. However, for many
complex data structures (e.g., longitudinal data), no rigorous approach has
been developed to address a fundamental issue: deleting subsets with different
numbers of observations introduces different degrees of perturbation to the
current model fitted to the data, and the magnitude of Cook's distance is
associated with the degree of the perturbation. The aim of this paper is to
address this issue in general parametric models with complex data structures.
We propose a new quantity for measuring the degree of the perturbation
introduced by deleting a subset. We use stochastic ordering to quantify the
stochastic relationship between the degree of the perturbation and the
magnitude of Cook's distance. We develop several scaled Cook's distances to
resolve the comparison of Cook's distance for different subset deletions.
Theoretical and numerical examples are examined to highlight the broad spectrum
of applications of these scaled Cook's distances in a formal influence
analysis.Comment: Published in at http://dx.doi.org/10.1214/12-AOS978 the Annals of
Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical
Statistics (http://www.imstat.org
Heat dissipation of high rate Li-SOCl sub 2 primary cells
The heat dissipation problem occurring in the lithium thionyl chloride cells discharged at relatively high rates under normal discharge conditions is examined. Four heat flow paths were identified, and the thermal resistances of the relating cell components along each flow path were accordingly calculated. From the thermal resistance network analysis, it was demonstrated that about 90 percent of the total heat produced within the cell should be dissipated along the radial direction in a spirally wound cell. In addition, the threshold value of the heat generation rate at which cell internal temperature could be maintained below 100 C, was calculated from total thermal resistance and found to be 2.9 W. However, these calculations were made only at the cell components' level, and the transient nature of the heat accumulation and dissipation was not considered. A simple transient model based on the lumped-heat-capacity concept was developed to predict the time-dependent cell temperature at different discharge rates. The overall objective was to examine the influence of cell design variable from the heat removal point of view under normal discharge conditions and to make recommendations to build more efficient lithium cells
Two-dimensional imaging of gauge fields in optical lattices
We propose a scheme to generate an arbitrary Abelian vector potential for
atoms trapped in a two-dimensional optical lattice. By making the optical
lattice potential dependent on the atomic state, we transform the problem into
that of a two-dimensional imaging. It is shown that an arbitrarily fine pattern
of the gauge field in the lattice can be realized without need of
diffraction-limited imaging.Comment: 4 pages, 3 figure
Light bottom squark and gluino confront electroweak precision measurements
We address the compatibility of a light sbottom (mass 2\sim 5.5 \gev) and a
light gluino (mass 12\sim 16 \gev) with electroweak precision measurements.
Such light particles have been suggested to explain the observed excess in the
quark production cross section at the Tevatron. The electroweak observables
may be affected by the sbottom and gluino through the SUSY-QCD corrections to
the vertex. We examine, in addition to the SUSY-QCD corrections, the
electroweak corrections to the gauge boson propagators from the stop which are
allowed to be light from the SU(2) symmetry. We find that this scenario is
strongly disfavored from electroweak precision measurements unless the heavier
sbottom mass eigenstate is lighter than 180\gev and the left-right mixing in
the stop sector is sufficiently large. This implies that one of the stops
should be lighter than about 98\gev.Comment: 4 pages, revtex, 2 figures. Reference added, version to appear in
Phys.Rev.Let
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