3,101 research outputs found
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
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
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
The uses of Connes and Kreimer's algebraic formulation of renormalization theory
We show how, modulo the distinction between the antipode and the "twisted" or
"renormalized" antipode, Connes and Kreimer's algebraic paradigm trivializes
the proofs of equivalence of the (corrected) Dyson-Salam,
Bogoliubov-Parasiuk-Hepp and Zimmermann procedures for renormalizing Feynman
amplitudes. We discuss the outlook for a parallel simplification of
computations in quantum field theory, stemming from the same algebraic
approach.Comment: 15 pages, Latex. Minor changes, typos fixed, 2 references adde
Quantum memory for squeezed light
We produce a 600-ns pulse of 1.86-dB squeezed vacuum at 795 nm in an optical
parametric amplifier and store it in a rubidium vapor cell for 1 us using
electromagnetically induced transparency. The recovered pulse, analyzed using
time-domain homodyne tomography, exhibits up to 0.21+-0.04 dB of squeezing. We
identify the factors leading to the degradation of squeezing and investigate
the phase evolution of the atomic coherence during the storage interval.Comment: To appear in PRL. Changes to version 3: we present a larger data set
featuring somewhat less squeezing, but also better statistics and a lower
margin of error. Some additional revisions are made in response to the
referees' comment
A One-Parameter Family of Hamiltonian Structures for the KP Hierarchy and a Continuous Deformation of the Nonlinear \W_{\rm KP} Algebra
The KP hierarchy is hamiltonian relative to a one-parameter family of Poisson
structures obtained from a generalized Adler map in the space of formal
pseudodifferential symbols with noninteger powers. The resulting \W-algebra
is a one-parameter deformation of \W_{\rm KP} admitting a central extension
for generic values of the parameter, reducing naturally to \W_n for special
values of the parameter, and contracting to the centrally extended
\W_{1+\infty}, \W_\infty and further truncations. In the classical limit,
all algebras in the one-parameter family are equivalent and isomorphic to
\w_{\rm KP}. The reduction induced by setting the spin-one field to zero
yields a one-parameter deformation of \widehat{\W}_\infty which contracts to
a new nonlinear algebra of the \W_\infty-type.Comment: 31 pages, compressed uuencoded .dvi file, BONN-HE-92/20, US-FT-7/92,
KUL-TF-92/20. [version just replaced was truncated by some mailer
Invariant Killing spinors in 11D and type II supergravities
We present all isotropy groups and associated groups, up to discrete
identifications of the component connected to the identity, of spinors of
eleven-dimensional and type II supergravities. The groups are products
of a Spin group and an R-symmetry group of a suitable lower dimensional
supergravity theory. Using the case of SU(4)-invariant spinors as a paradigm,
we demonstrate that the groups, and so the R-symmetry groups of
lower-dimensional supergravity theories arising from compactifications, have
disconnected components. These lead to discrete symmetry groups reminiscent of
R-parity. We examine the role of disconnected components of the groups
in the choice of Killing spinor representatives and in the context of
compactifications.Comment: 22 pages, typos correcte
Removal Efficiency of Cr6+ by Indigenous Pichia sp. Isolated from Textile Factory Effluent
Resistance of the indigenous strains P. jadinii M9 and P. anomala M10, to high Cr6+ concentrations and their ability to reduce chromium in culture medium was studied. The isolates were able to tolerate chromium concentrations up to 104 μg mL−1. Growth and reduction of Cr6+ were dependent on incubation temperature, agitation, Cr6+ concentration, and pH. Thus, in both studied strains the chromium removal was increased at 30°C with agitation. The optimum pH was different, with values of pH 3.0 and pH 7.0 in the case of P. anomala M10 and pH 7.0 using P. jadinii M9. Chromate reduction occurred both in intact cells (grown in culture medium) as well as in cell-free extracts. Chromate reductase activity could be related to cytosolic or membrane-associated proteins. The presence of a chromate reductase activity points out a possible role of an enzyme in Cr6+ reduction
Exact N=2 Supergravity Solutions With Polarized Branes
We construct several classes of exact supersymmetric supergravity solutions
describing D4 branes polarized into NS5 branes and F-strings polarized into D2
branes. These setups belong to the same universality class as the perturbative
solutions used by Polchinski and Strassler to describe the string dual of N=1*
theories. The D4-NS5 setup can be interpreted as a string dual to a confining
4+1 dimensional theory with 8 supercharges, whose properties we discuss. By
T-duality, our solutions give Type IIB supersymmetric backgrounds with
polarized branes.Comment: 22 pages. v2 - references added, details clarifie
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