528 research outputs found
On Brane Actions and Superembeddings
Actions for branes, with or without worldsurface gauge fields, are discussed
in a unified framework. A simple algorithm is given for constructing the
component Green-Schwarz actions. Superspace actions are also discussed. Three
examples are given to illustrate the general procedure: the membrane in D=11
and the D2-brane, which both have on-shell worldsurface supermultiplets, and
the membrane in D=4, which has an off-shell multiplet.Comment: 19 pages, late
Supersymmetric Higher Spin Theories
We revisit the higher spin extensions of the anti de Sitter algebra in four
dimensions that incorporate internal symmetries and admit representations that
contain fermions, classified long ago by Konstein and Vasiliev. We construct
the , Euclidean and Kleinian version of these algebras, as well as the
corresponding fully nonlinear Vasiliev type higher spin theories, in which the
reality conditions we impose on the master fields play a crucial role. The
supersymmetric higher spin theory in , on which we elaborate
further, is included in this class of models. A subset of Konstein-Vasiliev
algebras are the higher spin extensions of the superalgebras
for mod 4 and can be realized using
fermionic oscillators. We tensor the higher superalgebras of the latter kind
with appropriate internal symmetry groups and show that the mod 4
higher spin algebras are isomorphic to those with mod 4. We
describe the fully nonlinear higher spin theories based on these algebras as
well, and we elaborate further on the supersymmetric theory,
providing two equivalent descriptions one of which exhibits manifestly its
relation to the supersymmetric higher spin theory.Comment: 30 pages. Contribution to J. Phys. A special volume on "Higher Spin
Theories and AdS/CFT" edited by M. R. Gaberdiel and M. Vasilie
On a Three-Dimensional Gravity Model with Higher Derivatives
The purpose of this work is to present a model for 3D massive gravity with
topological and higher-derivative terms. Causality and unitarity are discussed
at tree-level. Power-counting renormalizability is also contemplated.Comment: 9 pages, Latex, no figures; to be published in Gen. Rel. Gra
An action principle for Vasiliev's four-dimensional higher-spin gravity
We provide Vasiliev's fully nonlinear equations of motion for bosonic gauge
fields in four spacetime dimensions with an action principle. We first extend
Vasiliev's original system with differential forms in degrees higher than one.
We then derive the resulting duality-extended equations of motion from a
variational principle based on a generalized Hamiltonian sigma-model action.
The generalized Hamiltonian contains two types of interaction freedoms: One set
of functions that appears in the Q-structure of the generalized curvatures of
the odd forms in the duality-extended system; and another set depending on the
Lagrange multipliers, encoding a generalized Poisson structure, i.e. a set of
polyvector fields of ranks two or higher in target space. We find that at least
one of the two sets of interaction-freedom functions must be linear in order to
ensure gauge invariance. We discuss consistent truncations to the minimal Type
A and B models (with only even spins), spectral flows on-shell and provide
boundary conditions on fields and gauge parameters that are compatible with the
variational principle and that make the duality-extended system equivalent, on
shell, to Vasiliev's original system.Comment: 37 pages. References added, corrected typo
Isotropic reconstruction of 3D fluorescence microscopy images using convolutional neural networks
Fluorescence microscopy images usually show severe anisotropy in axial versus
lateral resolution. This hampers downstream processing, i.e. the automatic
extraction of quantitative biological data. While deconvolution methods and
other techniques to address this problem exist, they are either time consuming
to apply or limited in their ability to remove anisotropy. We propose a method
to recover isotropic resolution from readily acquired anisotropic data. We
achieve this using a convolutional neural network that is trained end-to-end
from the same anisotropic body of data we later apply the network to. The
network effectively learns to restore the full isotropic resolution by
restoring the image under a trained, sample specific image prior. We apply our
method to synthetic and real datasets and show that our results improve
on results from deconvolution and state-of-the-art super-resolution techniques.
Finally, we demonstrate that a standard 3D segmentation pipeline performs on
the output of our network with comparable accuracy as on the full isotropic
data
M5-brane Effective Action as an On-shell Action in Supergravity
We show that the covariant effective action for M5-brane is a solution to the
Hamilton-Jacobi (H-J) equations of 11-dimensional supergravity. The solution to
the H-J equations reproduces the supergravity solution that represents the
M2-M5 bound states.Comment: 20 pages, references added, typos correcte
Higher Spin Gauge Theory and Holography: The Three-Point Functions
In this paper we calculate the tree level three-point functions of Vasiliev's
higher spin gauge theory in AdS4 and find agreement with the correlators of the
free field theory of N massless scalars in three dimensions in the O(N) singlet
sector. This provides substantial evidence that Vasiliev theory is dual to the
free field theory, thus verifying a conjecture of Klebanov and Polyakov. We
also find agreement with the critical O(N) vector model, when the bulk scalar
field is subject to the alternative boundary condition such that its dual
operator has classical dimension 2.Comment: 90 pages, 5 figures; v4, minor changes in the introductio
The finiteness of the four dimensional antisymmetric tensor field model in a curved background
A renormalizable rigid supersymmetry for the four dimensional antisymmetric
tensor field model in a curved space-time background is constructed. A closed
algebra between the BRS and the supersymmetry operators is only realizable if
the vector parameter of the supersymmetry is a covariantly constant vector
field. This also guarantees that the corresponding transformations lead to a
genuine symmetry of the model. The proof of the ultraviolet finiteness to all
orders of perturbation theory is performed in a pure algebraic manner by using
the rigid supersymmetry.Comment: 23 page
Couplings of self-dual tensor multiplet in six dimensions
The (1,0) supersymmetry in six dimensions admits a tensor multiplet which
contains a second-rank antisymmetric tensor field with a self-dual field
strength and a dilaton. We describe the fully supersymmetric coupling of this
multiplet to Yang-Mills multiplet, in the absence of supergravity. The
self-duality equation for the tensor field involves a Chern-Simons modified
field strength, the gauge fermions, and an arbitrary dimensionful parameter.Comment: 17 pages, latex, no figure
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