25 research outputs found
Black holes and stars in Horava-Lifshitz theory with projectability condition
We systematically study spherically symmetric static spacetimes filled with a
fluid in the Horava-Lifshitz theory of gravity with the projectability
condition, but without the detailed balance. We establish that when the
spacetime is spatially Ricci flat the unique vacuum solution is the de Sitter
Schwarzshcild solution, while when the spacetime has a nonzero constant
curvature, there exist two different vacuum solutions; one is an (Einstein)
static universe, and the other is a new spacetime. This latter spacetime is
maximally symmetric and not flat. We find all the perfect fluid solutions for
such spacetimes, in addition to a class of anisotropic fluid solutions of the
spatially Ricci flat spacetimes. To construct spacetimes that represent stars,
we investigate junction conditions across the surfaces of stars and obtain the
general matching conditions with or without the presence of infinitely thin
shells. It is remarkable that, in contrast to general relativity, the radial
pressure of a star does not necessarily vanish on its surface even without the
presence of a thin shell, due to the presence of high order derivative terms.
Applying the junction conditions to our explicit solutions, we show that it is
possible to match smoothly these solutions (all with nonzero radial pressures)
to vacuum spacetimes without the presence of thin matter shells on the surfaces
of stars.Comment: The relations between energy-momentum tensors used in HL theory and
GR are considered, and the singular behavior of the trace of extrinsic
curvature is presented. References are updated. Version to appear in Physical
Reviews D
Black holes and global structures of spherical spacetimes in Horava-Lifshitz theory
We systematically study black holes in the Horava-Lifshitz (HL) theory by
following the kinematic approach, in which a horizon is defined as the surface
at which massless test particles are infinitely redshifted. Because of the
nonrelativistic dispersion relations, the speed of light is unlimited, and test
particles do not follow geodesics. As a result, there are significant
differences in causal structures and black holes between general relativity
(GR) and the HL theory. In particular, the horizon radii generically depend on
the energies of test particles. Applying them to the spherical static vacuum
solutions found recently in the nonrelativistic general covariant theory of
gravity, we find that, for test particles with sufficiently high energy, the
radius of the horizon can be made as small as desired, although the
singularities can be seen in principle only by observers with infinitely high
energy. In these studies, we pay particular attention to the global structure
of the solutions, and find that, because of the
foliation-preserving-diffeomorphism symmetry, , they are
quite different from the corresponding ones given in GR, even though the
solutions are the same. In particular, the does not allow
Penrose diagrams. Among the vacuum solutions, some give rise to the structure
of the Einstein-Rosen bridge, in which two asymptotically flat regions are
connected by a throat with a finite non-zero radius. We also study slowly
rotating solutions in such a setup, and obtain all the solutions characterized
by an arbitrary function . The case reduces to the slowly
rotating Kerr solution obtained in GR.Comment: latex4, 15 figures. Some typos were correcte
Initial Systematic Investigations of the Landscape of Low Layer NAHE Extensions
The discovery that the number of physically consistent string vacua is on the
order of 10^500 has prompted several statistical studies of string
phenomenology. Contained here is one such study that focuses on the Weakly
Coupled Free Fermionic Heterotic String (WCFFHS) formalism. Presented are
systematic extensions of the well-known NAHE (Nanopoulos, Antoniadis, Hagelin,
Ellis) set of basis vectors, which have been shown to produce
phenomenologically realistic models. Statistics related to the number of
U(1)'s, gauge group factors, non-Abelian singlets, ST SUSYs, as well as the
gauge groups themselve are discussed for the full range of models produced as
well as models containing GUT groups only. Prior results of other large-scale
investigations are compared with these regarding the aforementioned quantities.
Statistical coupling between the gauge groups and the number of ST SUSYs is
also discussed, and it was found that for order-3 extensions there are more
models with enhanced ST SUSY when there is an exceptional group present. Also
discussed are some three-generation GUT models found in the data sets. These
models are unique because they come from basis vectors which still have a
geometric interpretation -- there are no "rank-cuts" in these models.Comment: 65 Pages, 31 Tables, 31 Figure