1,810 research outputs found
Kaehler submanifolds with parallel pluri-mean curvature
We investigate the local geometry of a class of K\"ahler submanifolds which generalize surfaces of constant mean curvature. The role of
the mean curvature vector is played by the -part (i.e. the -components) of the second fundamental form , which we call the
pluri-mean curvature. We show that these K\"ahler submanifolds are
characterized by the existence of an associated family of isometric
submanifolds with rotated second fundamental form. Of particular interest is
the isotropic case where this associated family is trivial. We also investigate
the properties of the corresponding Gauss map which is pluriharmonic.Comment: Plain TeX, 21 page
The Cosmological Time Function
Let be a time oriented Lorentzian manifold and the Lorentzian
distance on . The function is the cosmological
time function of , where as usual means that is in the causal
past of . This function is called regular iff for all
and also along every past inextendible causal curve. If the
cosmological time function of a space time is regular it has
several pleasant consequences: (1) It forces to be globally hyperbolic,
(2) every point of can be connected to the initial singularity by a
rest curve (i.e., a timelike geodesic ray that maximizes the distance to the
singularity), (3) the function is a time function in the usual sense, in
particular (4) is continuous, in fact locally Lipschitz and the second
derivatives of exist almost everywhere.Comment: 19 pages, AEI preprint, latex2e with amsmath and amsth
Rigid Singularity Theorem in Globally Hyperbolic Spacetimes
We show the rigid singularity theorem, that is, a globally hyperbolic
spacetime satisfying the strong energy condition and containing past trapped
sets, either is timelike geodesically incomplete or splits isometrically as
space time. This result is related to Yau's Lorentzian splitting
conjecture.Comment: 3 pages, uses revtex.sty, to appear in Physical Review
Multi-Terabyte EIDE Disk Arrays running Linux RAID5
High-energy physics experiments are currently recording large amounts of data
and in a few years will be recording prodigious quantities of data. New methods
must be developed to handle this data and make analysis at universities
possible. Grid Computing is one method; however, the data must be cached at the
various Grid nodes. We examine some storage techniques that exploit recent
developments in commodity hardware. Disk arrays using RAID level 5 (RAID-5)
include both parity and striping. The striping improves access speed. The
parity protects data in the event of a single disk failure, but not in the case
of multiple disk failures.
We report on tests of dual-processor Linux Software RAID-5 arrays and
Hardware RAID-5 arrays using a 12-disk 3ware controller, in conjunction with
250 and 300 GB disks, for use in offline high-energy physics data analysis. The
price of IDE disks is now less than $1/GB. These RAID-5 disk arrays can be
scaled to sizes affordable to small institutions and used when fast random
access at low cost is important.Comment: Talk from the 2004 Computing in High Energy and Nuclear Physics
(CHEP04), Interlaken, Switzerland, 27th September - 1st October 2004, 4
pages, LaTeX, uses CHEP2004.cls. ID 47, Poster Session 2, Track
Redundant Arrays of IDE Drives
The next generation of high-energy physics experiments is expected to gather
prodigious amounts of data. New methods must be developed to handle this data
and make analysis at universities possible. We examine some techniques that use
recent developments in commodity hardware. We test redundant arrays of
integrated drive electronics (IDE) disk drives for use in offline high-energy
physics data analysis. IDE redundant array of inexpensive disks (RAID) prices
now equal the cost per terabyte of million-dollar tape robots! The arrays can
be scaled to sizes affordable to institutions without robots and used when fast
random access at low cost is important. We also explore three methods of moving
data between sites; internet transfers, hot pluggable IDE disks in FireWire
cases, and writable digital video disks (DVD-R).Comment: Submitted to IEEE Transactions On Nuclear Science, for the 2001 IEEE
Nuclear Science Symposium and Medical Imaging Conference, 8 pages, 1 figure,
uses IEEEtran.cls. Revised March 19, 2002 and published August 200
Surgery and the Spectrum of the Dirac Operator
We show that for generic Riemannian metrics on a simply-connected closed spin
manifold of dimension at least 5 the dimension of the space of harmonic spinors
is no larger than it must be by the index theorem. The same result holds for
periodic fundamental groups of odd order.
The proof is based on a surgery theorem for the Dirac spectrum which says
that if one performs surgery of codimension at least 3 on a closed Riemannian
spin manifold, then the Dirac spectrum changes arbitrarily little provided the
metric on the manifold after surgery is chosen properly.Comment: 23 pages, 4 figures, to appear in J. Reine Angew. Mat
Invariant four-forms and symmetric pairs
We give criteria for real, complex and quaternionic representations to define
s-representations, focusing on exceptional Lie algebras defined by spin
representations. As applications, we obtain the classification of complex
representations whose second exterior power is irreducible or has an
irreducible summand of co-dimension one, and we give a conceptual
computation-free argument for the construction of the exceptional Lie algebras
of compact type.Comment: 16 pages [v2: references added, last section expanded
Convex Functions and Spacetime Geometry
Convexity and convex functions play an important role in theoretical physics.
To initiate a study of the possible uses of convex functions in General
Relativity, we discuss the consequences of a spacetime or an
initial data set admitting a suitably defined convex
function. We show how the existence of a convex function on a spacetime places
restrictions on the properties of the spacetime geometry.Comment: 26 pages, latex, 7 figures, improved version. some claims removed,
references adde
Volume Comparison for Hypersurfaces in Lorentzian Manifolds and Singularity Theorems
We develop area and volume comparison theorems for the evolution of
spacelike, acausal, causally complete hypersurfaces in Lorentzian manifolds,
where one has a lower bound on the Ricci tensor along timelike curves, and an
upper bound on the mean curvature of the hypersurface. Using these results, we
give a new proof of Hawking's singularity theorem.Comment: 15 pages, LaTe
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