14,958 research outputs found
Kaehler forms and cosmological solutions in type II supergravities
We consider cosmological solutions to type II supergravity theories where the
spacetime is split into a FRW universe and a K\"ahler space, which may be taken
to be Calabi-Yau. The various 2-forms present in the theories are taken to be
proportional to the K\"ahler form associated to the K\"ahler space.Comment: 6 pages, LaTeX2
Numerical Study of Cosmic Censorship in String Theory
Recently Hertog, Horowitz, and Maeda have argued that cosmic censorship can
be generically violated in string theory in anti-de Sitter spacetime by
considering a collapsing bubble of a scalar field whose mass saturates the
Breitenlohner-Freedman bound. We study this system numerically and find that
for various choices of initial data black holes form rather than naked
singularities, implying that in these cases cosmic censorship is upheld.Comment: 16 pages, latex, 10 figures, uses JHEP.cls, v2: minor changes,
version to be published in JHE
Black Holes in the Dilatonic Einstein-Gauss-Bonnet Theory in Various Dimensions II -- Asymptotically AdS Topological Black Holes --
We study asymptotically AdS topological black hole solutions with k=0 (plane
symmetric) in the Einstein gravity with Gauss-Bonnet term, the dilaton and a
"cosmological constant" in various dimensions. We derive the field equations
for suitable ansatz for general D dimensions. We determine the parameter
regions including dilaton couplings where such solutions exist and construct
black hole solutions of various masses numerically in D=4,5,6 and 10
dimensional spacetime with (D-2)-dimensional hypersurface of zero curvature.Comment: 24 pages, 8 figures, PTPTeX, typos correcte
Collapsing open isotropic universe generated by nonminimally coupled scalar field
We investigated the behavior of an open isotropic universe generated by a
scalar field which couples with background curvature nonminimally with the
coupling constant . In particular we focus on the situation where the
initial value for the scalar field is greater than the critical
value =. The behavior is similar
to an open de Sitter universe with with a negative cosmological constant
. It is found that the universe will collapse eventually to a
singularity and thus has a finite extent in time in the future. Furthermore,
there are some cases which shows a rebouncing behavior before the final
collapse.Comment: 8 pages, 3 ps files, submitted to Phys.Lett.
Static Axially Symmetric Solutions of Einstein-Yang-Mills-Dilaton Theory
We construct static axially symmetric solutions of SU(2)
Einstein-Yang-Mills-dilaton theory. Like their spherically symmetric
counterparts, these solutions are nonsingular and asymptotically flat. The
solutions are characterized by the winding number n and the node number k of
the gauge field functions. For fixed n with increasing k the solutions tend to
``extremal'' Einstein-Maxwell-dilaton black holes with n units of magnetic
charge.Comment: 11 pages, including 2 postscript figure
A Monte Carlo Study of the 6.4 keV Emission at the Galactic Center
Strong fluorescent Fe line emission at 6.4 keV has been observed from the Sgr
B2 giant molecular cloud located in the Galactic Center region. The large
equivalent width of this line and the lack of an apparent illuminating nearby
object indicate that a time-dependent source, currently in a low-activity
state, is causing the fluorescent emission. It has been suggested that this
illuminator is the massive black hole candidate, Sgr A*, whose X-ray luminosity
has declined by an unprecedented six orders of magnitude over the past 300
years. We here report the results of our Monte Carlo simulations for producing
this line under a variety of source configurations and characteristics. These
indicate that the source may in fact be embedded within Sgr B2, although
external sources give a slightly better fit to the data. The weakened
distinction between the internal and external illuminators is due in part to
the instrument response function, which accounts for an enhanced equivalent
width of the line by folding some of the continuum radiation in with the
intrinsic line intensity. We also point out that although the spectrum may be
largely produced by K emission in cold gas, there is some evidence in
the data to suggest the presence of warm (~10^5 K) emitting material near the
cold cloud.Comment: 11 pages, 4 figure
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