212 research outputs found
On initial conditions and global existence for accelerating cosmologies from string theory
We construct a solution satisfying initial conditions for accelerating
cosmologies from string/M-theory. Gowdy symmetric spacetimes with a positive
potential are considered. Also, a global existence theorem for the spacetimes
is shown.Comment: To appear in Annales Henri Poincar
On the existence of global solutions for -Gowdy spacetimes with stringy matter
We show a global existence theorem for Einstein-matter equations of
-Gowdy symmetric spacetimes with stringy matter. The areal time
coordinate is used. It is shown that this spacetime has a crushing singularity
into the past. From these results we can show that the spacetime is foliated by
compact hypersurfaces of constant mean curvature.Comment: 10 pages, to appear in Classical and Quantum Gravit
Investigation of evolution strategy and optimization of induction heating model
An optimal design method using the finite element method and the evolution strategy (ES) is investigated. The evolution strategy is applied to the optimization of induction heating model. The position of auxiliary coil, frequency and ampere-turns are optimized so that the distribution of eddy current density on the surface of steel becomes uniform. It is shown that the selection of the appropriate parameter is important in the practical application of ES</p
Global existence problem in -Gowdy symmetric IIB superstring cosmology
We show global existence theorems for Gowdy symmetric spacetimes with type
IIB stringy matter. The areal and constant mean curvature time coordinates are
used. Before coming to that, it is shown that a wave map describes the
evolution of this system
Effort-Reward Imbalance and Quality of Life Among Female Nurses at a General Hospital in Japan
The excitation of a charged string passing through a shock wave in a charged Aichelburg-Sexl spacetime
We investigate how much a first-quantized charged bosonic test string gets
excited after crossing a shock wave generated by a charged particle with mass
and charge . On the basis of Kaluza-Klein theory, we pay
attention to a closed string model where charge is given by a momentum along a
compactified extra-dimension. The shock wave is given by a charged
Aichelburg-Sexl (CAS) spacetime where corresponds to the ordinary
Aichelburg-Sexl one. We first show that the CAS spacetime is a solution to the
equations of motion for the metric, the gauge field, and the axion field in the
low-energy limit. Secondly, we compute the mass expectation value of the
charged test string after passing through the shock wave in the CAS spacetime.
In the case of small , gravitational and Coulomb forces are
canceled out each other and hence the excitation of the string remains very
small. This is independent of the particle mass or the strength of
the shock wave. In the case of large , however, every charged string
gets highly excited by quantum fluctuation in the extra-dimension caused by
both the gauge and the axion fields. This is quite different from classical
"molecule", which consists of two electrically charged particles connected by a
classical spring.Comment: Latex, 20 pages, no figures, accepted for Nucl. Phys.
Do naked singularities generically occur in generalized theories of gravity?
A new mechanism for causing naked singularities is found in an effective
superstring theory. We investigate the gravitational collapse in a spherically
symmetric Einstein-Maxwell-dilaton system in the presence of a pure
cosmological constant "potential", where the system has no static black hole
solution. We show that once gravitational collapse occurs in the system, naked
singularities necessarily appear in the sense that the field equations break
down in the domain of outer communications. This suggests that in generalized
theories of gravity, the non-minimally coupled fields generically cause naked
singularities in the process of gravitational collapse if the system has no
static or stationary black hole solution.Comment: 4 pages including 2 eps figures, to be published in Physical Review
Letter
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