4,855 research outputs found
Marginal Deformations as Lower Dimensional D-brane Solutions in Open String Field theory
By direct calculation we showed that a finite analytic solution for marginal
deformation of open string field theory, by a matter primary operator with
singular OPE, can be obtained to all orders in the deformation parameter. In
particular, we obtained solutions that describe lower dimensional D-branes and
our results agree with the results obtained when the same problem is treated in
the world-sheet conformal field theory language.Comment: 19 pages, 4 figure
Scalar Non-Luminous Matter in Galaxies
As a candidate for dark matter in galaxies, we study an SU(3) triplet of
complex scalar fields which are non-minimally coupled to gravity. In the
spherically symmetric static spacetime where the flat rotational velocity
curves of stars in galaxies can be explained, we find simple solutions of
scalar fields with SU(3) global symmetry broken to U(1) X U(1), in an
exponential scalar potential, which will be useful in a quintessence model of
the late-time acceleration of the Universe.Comment: 6 pages, no figure, LaTex. Submitted to IJMP
Domain wall cosmology and multiple accelerations
We classify the cosmological behaviors of the domain wall under junctions
between two spacetimes in terms of various parameters: cosmological constants
of bulk spacetime, a tension of a domain wall, and mass parameters of the black
hole-type metric. Especially, we consider the false-true vacuum type junctions
and the domain wall connecting between an inner AdS space and an outer AdS
Reissner-Nordstrm black hole. We find that there exist a
solution to the junction equations with an inflation at earlier times and an
accelerating expansion at later times.Comment: corrected typos, title and sec.
Cosmic String Spacetime in Dilaton Gravity and Flat Rotation Curves
In dilaton gravity theories, we consider a string-like topological defect
formed during U(1) gauge symmetry-breaking phase transition in the early
Universe, and far from the cosmic string we have vacuum solutions of the
generalized Einstein equation. We discuss how they can be related to the
flatness of galactic rotation curves.Comment: 9 pages, RevTeX4 fil
Synthesis, Crystal Structure and Properties of a Perovskite-Related Bismuth Phase, (NH4)3Bi2I9
Organic-inorganic halide perovskites, especially methylammonium lead halide,
have recently led to a remarkable breakthrough in photovoltaic devices.
However, due to the environmental and stability concerns of the heavy metal,
lead, in these perovskite based solar cells, research in the non-lead
perovskite structures have been attracting increasing attention. In this study,
a layered perovskite-like architecture, (NH4)3Bi2I9, was prepared in solution
and the structure was solved by single crystal X-ray diffraction. The results
from DFT calculations showed the significant lone pair effect of the bismuth
ion and the band gap was measured as around 2.04 eV, which is lower than the
band gap of CH3NH3PbBr3. Conductivity measurement was also performed to examine
the potential in the applications as an alternative to the lead containing
perovskites
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