26,200 research outputs found
Towards an exact frame formulation of conformal higher spins in three dimensions
In this note we discuss some aspects of the frame formulation of conformal
higher spins in three dimensions. We give some exact formulae for the coupled
spin two - spin three part of the full higher spin theory and propose a star
product Lagrangian for all spins from two and up. Since there is no consistent
Lagrangian formulation based on the Poisson bracket we start the construction
from the field equations in this approximation of the star product. The higher
spin algebra is then realized in terms of classical variables which leads to
certain important simplifications that we take advantage of. The suggested
structure of the all-spin Lagrangian given here is, however, obtained using an
expansion of the star product beyond the Poisson bracket in terms of
multi-commutators and the Lagrangian should be viewed as a starting point for
the derivation of the full theory based on a star product. How to do this is
explained as well as how to include the coupling to scalar fields. We also
comment on the AdS/CFT relation to four dimensions.Comment: 18 pages, v2: misprints corrected, an appendix, footnotes and some
clarifying remarks added, 21 page
On the conformal higher spin unfolded equation for a three-dimensional self-interacting scalar field
We propose field equations for the conformal higher spin system in three
dimensions coupled to a conformal scalar field with a sixth order potential.
Both the higher spin equation and the unfolded equation for the scalar field
have source terms and are based on a conformal higher spin algebra which we
treat as an expansion in multi-commutators. Explicit expressions for the source
terms are suggested and subjected to some simple tests. We also discuss a
cascading relation between the Chern-Simons action for the higher spin gauge
theory and an action containing a term for each spin that generalizes the spin
2 Chern-Simons action in terms of the spin connection expressed in terms of the
frame field. This cascading property is demonstrated in the free theory for
spin 3 but should work also in the complete higher spin theory.Comment: v2: 20 pages, misprints corrected, footnotes adde
General-purpose and special-purpose visual systems
The information that eyes supply supports a wide variety of functions, from the guidance systems that enable an animal to navigate successfully around the environment, to the detection and identification of predators, prey, and conspecifics. The eyes with which we are most familiar the single-chambered eyes of vertebrates and cephalopod molluscs, and the compound eyes of insects and higher crustaceans allow these animals to perform the full range of visual tasks. These eyes have evidently evolved in conjunction with brains that are capable of subjecting the raw visual information to many different kinds of analysis, depending on the nature of the task that the animal is engaged in. However, not all eyes evolved to provide such comprehensive information. For example, in bivalve molluscs we find eyes of very varied design (pinholes, concave mirrors, and apposition compound eyes) whose only function is to detect approaching predators and thereby allow the animal to protect itself by closing its shell. Thus, there are special-purpose eyes as well as eyes with multiple functions
Pure Spinors and D=6 Super-Yang-Mills
Pure spinor cohomology has been used to describe maximally supersymmetric
theories, like D=10 super-Yang-Mills and D=11 supergravity. Supersymmetry
closes on-shell in such theories, and the fields in the cohomology
automatically satisfy the equations of motion. In this paper, we investigate
the corresponding structure in a model with off-shell supersymmetry, N=1
super-Yang-Mills theory in D=6. Here, fields and antifields are obtained as
cohomologies in different complexes with respect to the BRST operator Q. It
turns out to be natural to enlarge the pure spinor space with additional
bosonic variables, subject to some constraints generalising the pure spinor
condition, in order to accommodate the different supermultiplets in the same
generalised pure spinor wave-function. We construct another BRST operator, s,
acting in the cohomology of Q, whose cohomology implies the equations of
motion. We comment on the possible use of similar approaches in other models.Comment: 11 pp, 3 figs, plain te
Butterfly Optics Exceed the Theoretical Limits of Conventional Apposition Eyes
Optical experiments on butterfly compound eyes show that they have angular sensitivities narrower than expected from conventional apposition eyes. This superior performance is explained by a theoretical model where the cone stalk is considered as a modecoupling device. In this model the Airy diffraction pattern of the corneal facet excites a combination of the two waveguide modes LP01 and LP02. When the two modes propagate through the cone stalk the power of LP02 is transferred to LP01 alone which is supported by the rhabdom. This mechanism produces a higher on-axis sensitivity and a narrower angular sensitivity than conventional apposition optics. Several predictions of the model were confirmed experimentally.
Empirical multi-wavelength prediction method for very high energy gamma-ray emitting BL Lacs
Aim: We have collected the most complete multi-wavelength () dataset of very high energy (VHE) -ray emitting (TeV) BL
Lacs, which are the most numerous extragalactic VHE sources. Using significant
correlations between different bands, we aim to identify the best TeV BL Lac
candidates that can be discovered by the current and next generation of imaging
air Cherenkov telescopes.
Methods: We formed five datasets from lower energy data, i.e. radio,
mid-infrared, optical, X-rays, and GeV -ray, and five VHE -ray
datasets to perform a correlation study between different bands and to
construct the prediction method. The low energy datasets were averaged for
individual sources, while the VHE -ray data were divided into subsets
according to the flux state of the source. We then looked for significant
correlations and determined their best-fit parameters. Using the best-fit
parameters we predicted the level of VHE -ray flux for a sample of 182
BL Lacs, which have not been detected at TeV energies. We identified the most
promising TeV BL Lac candidates based on the predicted VHE -ray flux
for each source.
Results: We found 14 significant correlations between radio, mid-infrared,
optical, -ray, and VHE -ray bands. The correlation between
optical and VHE -ray luminosity is established for the first time. We
attribute this to the more complete sample and more accurate handling of host
galaxy flux in our work. We found nine BL Lac candidates whose predicted VHE
-ray flux is high enough for detection in less than 25 hours with
current imaging air Cherenkov telescopes.Comment: 10 pages, 2 figures, 4 Table
A Note on Topological M5-branes and String-Fivebrane Duality
We derive the stability conditions for the M5-brane in topological M-theory
using kappa-symmetry. The non-linearly self-dual 3-form on the world-volume is
necessarily non-vanishing, as is the case also for the 2-form field strengths
on coisotropic branes in topological string theory. It is demonstrated that the
self-duality is consistent with the stability conditions, which are solved
locally in terms of a tensor in the representation 6 of SU(3) in G_2. The
double dimensional reduction of the M5-brane is the D4-brane, and its direct
reduction is an NS5-brane. We show that the equation of motion for the 3-form
on the NS5-brane wrapping a Calabi-Yau space is exactly the Kodaira-Spencer
equation, providing support for a string-fivebrane duality in topological
string theory.Comment: 11 pp, plain te
On relating multiple M2 and D2-branes
Due to the difficulties of finding superconformal Lagrangian theories for
multiple M2-branes, we will in this paper instead focus on the field equations.
By relaxing the requirement of a Lagrangian formulation we can explore the
possibility of having structure constants satisfying the
fundamental identity but which are not totally antisymmetric. We exemplify this
discussion by making use of an explicit choice of a non-antisymmetric
constructed from the Lie algebra structure constants
of an arbitrary gauge group. Although this choice of does not
admit an obvious Lagrangian description, it does reproduce the correct SYM
theory for a stack of D2-branes to leading order in upon
reduction and, moreover, it sheds new light on the centre of mass coordinates
for multiple M2-branes.Comment: 9 pages, references added and statements concerning the fundamental
identity revise
Manifestly supersymmetric M-theory
In this paper, the low-energy effective dynamics of M-theory,
eleven-dimensional supergravity, is taken off-shell in a manifestly
supersymmetric formulation. We show that a previously proposed relaxation of
the superspace torsion constraints does indeed accommodate a current
supermultiplet which lifts the equations of motion corresponding to the
ordinary second order derivative supergravity lagrangian. Whether the auxiliary
fields obtained this way can be used to construct an off-shell lagrangian is
not yet known. We comment on the relation and application of this completely
general formalism to higher-derivative (R^4) corrections. Some details of the
calculation are saved for a later publication.Comment: 13 pages, plain tex. v2: minor changes, one ref. adde
- …