93 research outputs found
Strings in Nontrivial Gravitino and Ramond-Ramond Backgrounds
In this paper we discuss deformations of the BRST operator of the fermionic
string. These deformations preserve nilpotency of the BRST operator and
correspond to turning on infinitesimal Gravitino and Ramond-Ramond spacetime
fields.Comment: 6 pages, Latex; Based on a talk given at the 10th International
Symposium on String Theory, Towha University, Fukuoka, Japan, July 200
Covariance Eigenvector Sparsity for Compression and Denoising
Sparsity in the eigenvectors of signal covariance matrices is exploited in
this paper for compression and denoising. Dimensionality reduction (DR) and
quantization modules present in many practical compression schemes such as
transform codecs, are designed to capitalize on this form of sparsity and
achieve improved reconstruction performance compared to existing
sparsity-agnostic codecs. Using training data that may be noisy a novel
sparsity-aware linear DR scheme is developed to fully exploit sparsity in the
covariance eigenvectors and form noise-resilient estimates of the principal
covariance eigenbasis. Sparsity is effected via norm-one regularization, and
the associated minimization problems are solved using computationally efficient
coordinate descent iterations. The resulting eigenspace estimator is shown
capable of identifying a subset of the unknown support of the eigenspace basis
vectors even when the observation noise covariance matrix is unknown, as long
as the noise power is sufficiently low. It is proved that the sparsity-aware
estimator is asymptotically normal, and the probability to correctly identify
the signal subspace basis support approaches one, as the number of training
data grows large. Simulations using synthetic data and images, corroborate that
the proposed algorithms achieve improved reconstruction quality relative to
alternatives.Comment: IEEE Transcations on Signal Processing, 2012 (to appear
Supersymmetry and Gravitational Quadrupoles
We derive model independent, non-perturbative supersymmetric sum rules for
the gravitational quadrupole moments of arbitrary-spin particles in any N=1
supersymmetric theory. These sum rules select a ``preferred'' value of h=1
where the ``h-factor'' is the gravitational quadrupole analog of the
gyromagnetic ratio or g-factor. This value of h=1 corresponds identically to
the preferred field theory value obtained by tree-level unitarity
considerations. The presently derived h-factor sum rule complements and
generalizes previous work on electromagnetic moments where g=2 was shown to be
preferred by both supersymmetric sum rule and tree-level unitarity arguments.Comment: 10 pages, plain Te
Massive Higher Spin States in String Theory and the Principle of Equivalence
In this paper we study three point functions of the Type II superstring
involving one graviton and two massive states, focusing in particular on the
spin-7/2 fermions at the first mass level. Defining a gravitational quadrupole
``h-factor'', we find that the non-minimal interactions of string states in
general are parametrized by , in contrast to the preferred field theory
value of h=1 (for tree-level unitarity). This difference arises from the fact
that consistent gravitational interactions of strings are related to the
presence of a complete tower of massive states, not present in the ordinary
field theory case.Comment: 14 pages, plain Te
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