8,461 research outputs found
Existence of CMC Cauchy surfaces and spacetime splitting
In this paper, we review results on the existence (and nonexistence) of
constant mean curvature spacelike hypersurfaces in the cosmological setting,
and discuss the connection to the spacetime splittng problem. It is a pleasure
to dedicate this paper to Robert Bartnik, who has made fundamental
contributions to this area.Comment: 16 page
Nomenclatural notes on Pseudocyphellaria V : some Brazilian taxa
A new, phyllidiate, white-medulla species with yellow pseudocyphellae and a green photobiont, Pseudocyphellaria kalbii D.J.Galloway, is described from Brazilian collections, and typification and notes on P. aurora (De Not.) Vainio are presented
Studies on the lichen genus Sticta (Schreber) Ach. : 5., Australian species
Twenty five species of Sticta occur in Australia. These are: Sticta baileyi, S. brevipes, S. camarae, S. caperata, S. cyphellulata, S. diversa, S. duplolimbata, S. filix, S. flavocyphellata, S. fuliginosa, S. howei, S. hypopsiloides, S. latifrons, S. limbata, S. marginifera, S. myrioclada, S. pedunculata, S. rutilans, S. sayeri, S. stipitata, S. sublimbata, S. subtomentella, S. variabilis and S. weigelii. A key and descriptions of each taxon are given together with details of biogeography, distribution, ecology and nomenclature. Sticta baileyi, S. flavocyphellata and S. howei are newly described, and Sticta myrioloba (MĂĽll.Arg.) D.J.Galloway comb. & stat. nov., is proposed
Maximum Principles for Null Hypersurfaces and Null Splitting Theorems
A maximum principle for C^0 null hypersurfaces is obtained and used to derive
a splitting theorem for spacetimes which contain null lines. As a consequence
of this null splitting theorem, it is proved that an asymptotically simple
vacuum (Ricci flat) spacetime which contains a null line is isometric to
Minkowski space.Comment: 26 pages, latex2
Rigidity of outermost MOTS - the initial data version
In [5], a rigidity result was obtained for outermost marginally outer trapped
surfaces (MOTSs) that do not admit metrics of positive scalar curvature. This
allowed one to treat the "borderline case" in the author's work with R. Schoen
concerning the topology of higher dimensional black holes [8]. The proof of
this rigidity result involved bending the initial data manifold in the vicinity
of the MOTS within the ambient spacetime. In this note we show how to
circumvent this step, and thereby obtain a pure initial data version of this
rigidity result and its consequence concerning the topology of black holes.Comment: 8 pages; v2: minor changes; version to appear in GR
Singularity theorems from weakened energy conditions
We establish analogues of the Hawking and Penrose singularity theorems based
on (a) averaged energy conditions with exponential damping; (b) conditions on
local stress-energy averages inspired by the Quantum Energy Inequalities
satisfied by a number of quantum field theories. As particular applications, we
establish singularity theorems for the Einstein equations coupled to a
classical scalar field, which violates the strong energy condition, and the
nonminimally coupled scalar field, which also violates the null energy
condition.Comment: v3 18 pages. Minor correction to the proof of Lemma 3.1; results are
unchanged. Final version to appear in Class Quantum Gra
Historical development of noise exposure metrics
Some of the historical events that led to the introduction of night penalties are reported with emphasis on what happens with different kinds of day/night operations when night pentalties are employed. These effects are considered in terms of the difference between a nighttime weighting cumulative measure of noise exposure verses simply not using any night weighting at all, in decibles
dS/CFT and spacetime topology
Motivated by recent proposals for a de Sitter version of the AdS/CFT
correspondence, we give some topological restrictions on spacetimes of de
Sitter type, i.e., spacetimes with , which admit a regular past
and/or future conformal boundary. For example we show that if , , is a globally hyperbolic spacetime obeying suitable energy conditions,
which is of de Sitter type, with a conformal boundary to both the past and
future, then if one of these boundaries is compact, it must have finite
fundamental group and its conformal class must contain a metric of positive
scalar curvature. Our results are closely related to theorems of Witten and Yau
hep-th/9910245 pertaining to the Euclidean formulation of the AdS/CFT
correspondence.Comment: 16 pages, Latex2e, v2: reference corrected, v3: reference added,
material added to the introductio
On the Gannon-Lee Singularity Theorem in Higher Dimensions
The Gannon-Lee singularity theorems give well-known restrictions on the
spatial topology of singularity-free (i.e., nonspacelike geodesically
complete), globally hyperbolic spacetimes. In this paper, we revisit these
classic results in the light of recent developments, especially the failure in
higher dimensions of a celebrated theorem by Hawking on the topology of black
hole horizons. The global hyperbolicity requirement is weakened, and we expand
the scope of the main results to allow for the richer variety of spatial
topologies which are likely to occur in higher-dimensional spacetimes.Comment: 13 pages, no figures, to appear in Class. Quantum Gra
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