2,615 research outputs found
M-Horizons
We solve the Killing spinor equations and determine the near horizon
geometries of M-theory that preserve at least one supersymmetry. The M-horizon
spatial sections are 9-dimensional manifolds with a Spin(7) structure
restricted by geometric constraints which we give explicitly. We also provide
an alternative characterization of the solutions of the Killing spinor
equation, utilizing the compactness of the horizon section and the field
equations, by proving a Lichnerowicz type of theorem which implies that the
zero modes of a Dirac operator coupled to 4-form fluxes are Killing spinors. We
use this, and the maximum principle, to solve the field equations of the theory
for some special cases and present some examples.Comment: 36 pages, latex. Reference added, minor typos correcte
All null supersymmetric backgrounds of N=2, D=4 gauged supergravity coupled to abelian vector multiplets
The lightlike supersymmetric solutions of N=2, D=4 gauged supergravity
coupled to an arbitrary number of abelian vector multiplets are classified
using spinorial geometry techniques. The solutions fall into two classes,
depending on whether the Killing spinor is constant or not. In both cases, we
give explicit examples of supersymmetric backgrounds. Among these BPS
solutions, which preserve one quarter of the supersymmetry, there are
gravitational waves propagating on domain walls or on bubbles of nothing that
asymptote to AdS_4. Furthermore, we obtain the additional constraints obeyed by
half-supersymmetric vacua. These are divided into four categories, that include
bubbles of nothing which are asymptotically AdS_4, pp-waves on domain walls,
AdS_3 x R, and spacetimes conformal to AdS_3 times an interval.Comment: 55 pages, uses JHEP3.cls. v2: Minor errors corrected, small changes
in introductio
Control of large space structures
The control of large space structures was studied to determine what, if any, limitations are imposed on the size of spacecraft which may be controlled using current control system design technology. Using a typical structure in the 35 to 70 meter size category, a control system design that used actuators that are currently available was designed. The amount of control power required to maintain the vehicle in a stabilized gravity gradient pointing orientation that also damped various structural motions was determined. The moment of inertia and mass properties of this structure were varied to verify that stability and performance were maintained. The study concludes that the structure's size is required to change by at least a factor of two before any stability problems arise. The stability margin that is lost is due to the scaling of the gravity gradient torques (the rigid body control) and as such can easily be corrected by changing the control gains associated with the rigid body control. A secondary conclusion from the study is that the control design that accommodates the structural motions (to damp them) is a little more sensitive than the design that works on attitude control of the rigid body only
LabView Interface for School-Network DAQ Card
A low-cost DAQ card has been developed for school-network cosmic ray detector
projects, providing digitized data from photomultiplier tubes via a standard
serial interface. To facilitate analysis of these data and to provide students
with a starting point for custom readout systems, a model interface has been
developed using the National Instruments LabVIEW(R) system. This user-friendly
interface allows one to initialize the trigger coincidence conditions for
data-taking runs and to monitor incoming or pre-recorded data sets with
updating singles- and coincidence-rate plots and other user-selectable
histograms.Comment: 4 pages, 6 figures. Presented as Paper NS26-119 at IEEE-NSS 2003,
Portland, OR, by R. J. Wilke
Solutions of Minimal Four Dimensional de Sitter Supergravity
Pseudo-supersymmetric solutions of minimal , de Sitter
supergravity are classified using spinorial geometry techniques. We find three
classes of solutions. The first class of solution consists of geometries which
are fibrations over a 3-dimensional manifold equipped with a Gauduchon-Tod
structure. The second class of solution is the cosmological Majumdar-Papapetrou
solution of Kastor and Traschen, and the third corresponds to gravitational
waves propagating in the Nariai cosmology.Comment: 17 Pages. Minor correction to section 4; equation (4.21) corrected
and (old) equation (4.26) deleted; the final result is unchange
All the supersymmetric solutions of N=1,d=5 ungauged supergravity
We classify the supersymmetric solutions of ungauged N=1 d=5 SUGRA coupled to
vector multiplets and hypermultiplets. All the solutions can be seen as
deformations of solutions with frozen hyperscalars. We show explicitly how the
5-dimensional Reissner-Nordstrom black hole is deformed when hyperscalars are
living on SO(4,1)/SO(4) are turned on, reducing its supersymmetry from 1/2 to
1/8. We also describe in the timelike and null cases the solutions that have
one extra isometry and can be reduced to N=2,d=4 solutions. Our formulae allows
the uplifting of certain N=2,d=4 black holes to N=1,d=5 black holes on KK
monopoles or to pp-waves propagating along black strings.Comment: Some typos fixed and some paragraphs improved. 44 pages, Latex 2e
file, no figures. Version to be published in JHE
The spinorial geometry of supersymmetric heterotic string backgrounds
We determine the geometry of supersymmetric heterotic string backgrounds for
which all parallel spinors with respect to the connection with
torsion , the NSNS three-form field strength, are Killing. We find
that there are two classes of such backgrounds, the null and the timelike. The
Killing spinors of the null backgrounds have stability subgroups
K\ltimes\bR^8 in , for , SU(4), , and , and the Killing spinors of the timelike backgrounds have
stability subgroups , SU(3), SU(2) and . The former admit a single
null -parallel vector field while the latter admit a timelike and
two, three, five and nine spacelike -parallel vector fields,
respectively. The spacetime of the null backgrounds is a Lorentzian
two-parameter family of Riemannian manifolds with skew-symmetric torsion.
If the rotation of the null vector field vanishes, the holonomy of the
connection with torsion of is contained in . The spacetime of time-like
backgrounds is a principal bundle with fibre a Lorentzian Lie group and
base space a suitable Riemannian manifold with skew-symmetric torsion. The
principal bundle is equipped with a connection which determines the
non-horizontal part of the spacetime metric and of . The curvature of
takes values in an appropriate Lie algebra constructed from that of
. In addition has only horizontal components and contains the
Pontrjagin class of . We have computed in all cases the Killing spinor
bilinears, expressed the fluxes in terms of the geometry and determine the
field equations that are implied by the Killing spinor equations.Comment: 73pp. v2: minor change
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