5,335 research outputs found
IIB solutions with N>28 Killing spinors are maximally supersymmetric
We show that all IIB supergravity backgrounds which admit more than 28
Killing spinors are maximally supersymmetric. In particular, we find that for
all N>28 backgrounds the supercovariant curvature vanishes, and that the
quotients of maximally supersymmetric backgrounds either preserve all 32 or
N<29 supersymmetries.Comment: 27 page
The return of the four- and five-dimensional preons
We prove the existence of 3/4-BPS preons in four- and five-dimensional gauged
supergravities by explicitly constructing them as smooth quotients of the AdS_4
and AdS_5 maximally supersymmetric backgrounds, respectively. This result
illustrates how the spacetime topology resurrects a fraction of supersymmetry
previously ruled out by the local analysis of the Killing spinor equations.Comment: 10 pages (a minor imprecision has been corrected
Classification of IIB backgrounds with 28 supersymmetries
We show that all IIB backgrounds with strictly 28 supersymmetries are locally
isometric to the plane wave solution of arXiv:hep-th/0206195. Moreover, we
demonstrate that all solutions with more than 26 supersymmetries and only
5-form flux are maximally supersymmetric. The N=28 plane wave solution is a
superposition of the maximally supersymmetric IIB plane wave with a heterotic
string solution. We investigate the propagation of strings in this background,
find the spectrum and give the string light-cone Hamiltonian.Comment: 30 pages, typos correcte
PP-waves on Superbrane Backgrounds
In this paper we discuss a method of generating supersymmetric solutions of
the Einstein equations. The method involves the embedding of one supersymmetric
spacetime into another. We present two examples with constituent spacetimes
which support "charges", one of which was known previously and the other of
which is new. Both examples have PP-waves as one of the embedding constituents.Comment: 6 pages no figure
The holonomy of IIB supercovariant connection
We show that the holonomy of the supercovariant connection of IIB
supergravity is contained in SL(32, \bR). We also find that the holonomy
reduces to a subgroup of SL(32-N)\st (\oplus^N \bR^{32-N}) for IIB
supergravity backgrounds with Killing spinors. We give the necessary and
sufficient conditions for a IIB background to admit Killing spinors. A IIB
supersymmetric probe configuration can involve up to 31 linearly independent
planar branes and preserves one supersymmetry.Comment: 8 pages, latex. v2: Minor correction
A study of the Mg II 2796.34 A emission line in late--type normal, and RS CVn stars
We carry out an analysis of the Mg II 2796.34 A emission line in RS CVn stars
and make a comparison with the normal stars studied in a previous paper (Paper
I). The sample of RS CVn stars consists of 34 objects with known HIPPARCOS
parallaxes and observed at high resolution with IUE. We confirm that RS CVn
stars tend to possess wider Mg II lines than normal stars having the same
absolute visual magnitude. However, we could not find any correlation between
the logarithmic line width log Wo and the absolute visual magnitude Mv (the
Wilson--Bappu relationship) for these active stars, contrary to the case of
normal stars addressed in Paper I. On the contrary, we find that a strong
correlation exists in the (Mv, log L) plane (L is the absolute flux in the
line). In this plane, normal and RS CVn stars are distributed along two nearly
parallel straight lines with RS CVn stars being systematically brighter by
about 1 dex. Such a diagram provides an interesting tool to discriminate active
from normal stars. We finally analyse the distribution of RS CVn and of normal
stars in the (log L, log Wo) plane, and find a strong linear correlation for
normal stars, which can be used for distance determinations.Comment: 10 pages, 7 figures, latex, to be published in A&
On the maximal superalgebras of supersymmetric backgrounds
In this note we give a precise definition of the notion of a maximal
superalgebra of certain types of supersymmetric supergravity backgrounds,
including the Freund-Rubin backgrounds, and propose a geometric construction
extending the well-known construction of its Killing superalgebra. We determine
the structure of maximal Lie superalgebras and show that there is a finite
number of isomorphism classes, all related via contractions from an
orthosymplectic Lie superalgebra. We use the structure theory to show that
maximally supersymmetric waves do not possess such a maximal superalgebra, but
that the maximally supersymmetric Freund-Rubin backgrounds do. We perform the
explicit geometric construction of the maximal superalgebra of AdS_4 x S^7 and
find that is isomorphic to osp(1|32). We propose an algebraic construction of
the maximal superalgebra of any background asymptotic to AdS_4 x S^7 and we
test this proposal by computing the maximal superalgebra of the M2-brane in its
two maximally supersymmetric limits, finding agreement.Comment: 17 page
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