827 research outputs found
Super-Chern-Simons Theory as Superstring Theory
Superstrings and topological strings with supermanifolds as target space play
a central role in the recent developments in string theory. Nevertheless the
rules for higher-genus computations are still unclear or guessed in analogy
with bosonic and fermionic strings. Here we present a common geometrical
setting to develop systematically the prescription for amplitude computations.
The geometrical origin of these difficulties is the theory of integration of
superforms. We provide a translation between the theory of supermanifolds and
topological strings with supertarget space. We show how in this formulation one
can naturally construct picture changing operators to be inserted in the
correlation functions to soak up the zero modes of commuting ghost and we
derive the amplitude prescriptions from the coupling with an extended
topological gravity on the worldsheet. As an application we consider a simple
model on R^(3|2) leading to super-Chern-Simons theory.Comment: hravmac, 50p
The removal of shear-ellipticity correlations from the cosmic shear signal: Influence of photometric redshift errors on the nulling technique
Cosmic shear is regarded one of the most powerful probes to reveal the
properties of dark matter and dark energy. To fully utilize its potential, one
has to be able to control systematic effects down to below the level of the
statistical parameter errors. Particularly worrisome in this respect is
intrinsic alignment, causing considerable parameter biases via correlations
between the intrinsic ellipticities of galaxies and the gravitational shear,
which mimic lensing. In an earlier work we have proposed a nulling technique
that downweights this systematic, only making use of its well-known redshift
dependence. We assess the practicability of nulling, given realistic conditions
on photometric redshift information. For several simplified intrinsic alignment
models and a wide range of photometric redshift characteristics we calculate an
average bias before and after nulling. Modifications of the technique are
introduced to optimize the bias removal and minimize the information loss by
nulling. We demonstrate that one of the presented versions is close to optimal
in terms of bias removal, given high quality of photometric redshifts. For
excellent photometric redshift information, i.e. at least 10 bins with a small
dispersion, a negligible fraction of catastrophic outliers, and precise
knowledge about the redshift distributions, one version of nulling is capable
of reducing the shear-intrinsic ellipticity contamination by at least a factor
of 100. Alternatively, we describe a robust nulling variant which suppresses
the systematic signal by about 10 for a very broad range of photometric
redshift configurations. Irrespective of the photometric redshift quality, a
loss of statistical power is inherent to nulling, which amounts to a decrease
of the order 50% in terms of our figure of merit.Comment: 26 pages, including 16 figures; minor changes to match accepted
version; published in Astronomy and Astrophysic
Spurious Shear in Weak Lensing with LSST
The complete 10-year survey from the Large Synoptic Survey Telescope (LSST)
will image 20,000 square degrees of sky in six filter bands every few
nights, bringing the final survey depth to , with over 4 billion
well measured galaxies. To take full advantage of this unprecedented
statistical power, the systematic errors associated with weak lensing
measurements need to be controlled to a level similar to the statistical
errors.
This work is the first attempt to quantitatively estimate the absolute level
and statistical properties of the systematic errors on weak lensing shear
measurements due to the most important physical effects in the LSST system via
high fidelity ray-tracing simulations. We identify and isolate the different
sources of algorithm-independent, \textit{additive} systematic errors on shear
measurements for LSST and predict their impact on the final cosmic shear
measurements using conventional weak lensing analysis techniques. We find that
the main source of the errors comes from an inability to adequately
characterise the atmospheric point spread function (PSF) due to its high
frequency spatial variation on angular scales smaller than in the
single short exposures, which propagates into a spurious shear correlation
function at the -- level on these scales. With the large
multi-epoch dataset that will be acquired by LSST, the stochastic errors
average out, bringing the final spurious shear correlation function to a level
very close to the statistical errors. Our results imply that the cosmological
constraints from LSST will not be severely limited by these
algorithm-independent, additive systematic effects.Comment: 22 pages, 12 figures, accepted by MNRA
Fast, uniform, and compact scalar multiplication for elliptic curves and genus 2 Jacobians with applications to signature schemes
We give a general framework for uniform, constant-time one-and
two-dimensional scalar multiplication algorithms for elliptic curves and
Jacobians of genus 2 curves that operate by projecting to the x-line or Kummer
surface, where we can exploit faster and more uniform pseudomultiplication,
before recovering the proper "signed" output back on the curve or Jacobian.
This extends the work of L{\'o}pez and Dahab, Okeya and Sakurai, and Brier and
Joye to genus 2, and also to two-dimensional scalar multiplication. Our results
show that many existing fast pseudomultiplication implementations (hitherto
limited to applications in Diffie--Hellman key exchange) can be wrapped with
simple and efficient pre-and post-computations to yield competitive full scalar
multiplication algorithms, ready for use in more general discrete
logarithm-based cryptosystems, including signature schemes. This is especially
interesting for genus 2, where Kummer surfaces can outperform comparable
elliptic curve systems. As an example, we construct an instance of the Schnorr
signature scheme driven by Kummer surface arithmetic
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