63,594 research outputs found
New vacuum solutions of conformal Weyl gravity
The Bach equation, i.e., the vacuum field equation following from the
Lagrangian L=C_{ijkl}C^{ijkl}, will be completely solved for the case that the
metric is conformally related to the cartesian product of two 2-spaces; this
covers the spherically and the plane symmetric space-times as special subcases.
Contrary to other approaches, we make a covariant 2+2-decomposition of the
field equation, and so we are able to apply results from 2-dimensional gravity.
Finally, some cosmological solutions will be presented and discussed.Comment: 15 pages, LaTeX, no figures, submitted to J. Math. Phy
Geometry-induced localization of thermal fluctuations in ultrathin superconducting structures
Thermal fluctuations of the order parameter in an ultrathin triangular shaped
superconducting structure are studied near , in zero applied field. We
find that the order parameter is prone to much larger fluctuations in the
corners of the structure as compared to its interior. This geometry-induced
localization of thermal fluctuations is attributed to the fact that condensate
confinement in the corners is characterised by a lower effective
dimensionality, which favors stronger fluctuations.Comment: 9 pages, 5 figure
Coupled fermion and boson production in a strong background mean-field
We derive quantum kinetic equations for fermion and boson production starting
from a phi^4 Lagrangian with minimal coupling to fermions. Decomposing the
scalar field into a mean-field part and fluctuations we obtain spontaneous pair
creation driven by a self-interacting strong background field. The produced
fermion and boson pairs are self-consistently coupled. Consequently back
reactions arise from fermion and boson currents determining the time dependent
self-interacting background mean-field. We explore the numerical solution in
flux tube geometry for the time evolution of the mean-field as well as for the
number- and energy densities for fermions and bosons. We find that after a
characteristic time all energy is converted from the background mean-field to
particle creation. Applying this general approach to the production of
``quarks'' and ``gluons'' a typical time scale for the collapse of the flux
tube is 1.5 fm/c.Comment: 9 pages, latex, epsfig, 7 figure
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