279 research outputs found
A Framework for the Landscape
It seems likely that string theory has a landscape of vacua that includes
very many metastable de Sitter spaces. However, as emphasized by Banks, Dine
and Gorbatov, no current framework exists for examining these metastable vacua
in string theory. In this paper we attempt to correct this situation by
introducing an eternally inflating background in which the entire collection of
accelerating cosmologies is present as intermediate states. The background is a
classical solution which consists of a bubble of zero cosmological constant
inside de Sitter space, separated by a domain wall. At early and late times the
flat space region becomes infinitely big, so an S-matrix can be defined.
Quantum mechanically, the system can tunnel to an intermediate state which is
pure de Sitter space. We present evidence that a string theory S-matrix makes
sense in this background and contains metastable de Sitter space as an
intermediate state.Comment: 29+13 pages, 25 figures; v2: minor corrections, references adde
Complete Classification of Four-Dimensional Black Hole and Membrane Solutions in IR-modified Ho\v{r}ava Gravity
Ho\v{r}ava gravity has been proposed as a renormalizable, higher-derivative
gravity without ghost problems, by considering different scaling dimensions for
space and time. In the non-relativistic higher-derivative generalization of
Einstein gravity, the meaning and physical properties of black hole and
membrane space-times are quite different from the conventional ones. Here, we
study the singularity and horizon structures of such geometries in IR-modified
Ho\v{r}ava gravity, where the so-called "detailed balance" condition is softly
broken in IR. We classify all the viable static solutions without naked
singularities and study its close connection to non-singular cosmology
solutions. We find that, in addition to the usual point-like singularity at
, there exists a "surface-like" curvature singularity at finite
which is the cutting edge of the real-valued space-time. The degree of
divergence of such singularities is milder than those of general relativity,
and the Hawking temperature of the horizons diverges when they coincide with
the singularities. As a byproduct we find that, in addition to the usual
"asymptotic limit," a consistent flow of coupling constants, that we called "GR
flow limit," is needed in order to recover general relativity in the IR.Comment: Accepted in JHEP, Typos correcte
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