Selfdual strings and loop space Nahm equations

We give two independent arguments why the classical membrane fields should be loops. The first argument comes from how we may construct selfdual strings in the M5 brane from a loop space version of the Nahm equations. The second argument is that there appears to be no infinite set of finite-dimensional Lie algebras (such as $su(N)$ for any $N$) that satisfies the algebraic structure of the membrane theory.Comment: 28 pages, various additional comment

The non-Abelian tensor multiplet in loop space

We introduce a non-Abelian tensor multiplet directly in the loop space associated with flat six-dimensional Minkowski space-time, and derive the supersymmetry variations for on-shell ${\cal{N}}=(2,0)$ supersymmetry.Comment: 11 pages, v2: cleaner presentation, mistakes are corrected (and an erroneous section was removed

Loop space, (2,0) theory, and solitonic strings

We present an interacting action that lives in loop space, and we argue that this is a generalization of the theory for a free tensor multiplet. From this action we derive the Bogomolnyi equation corresponding to solitonic strings. Using the Hopf map, we find a correspondence between BPS strings and BPS monopoles in four-dimensional super Yang-Mills theory. This enable us to find explicit BPS saturated solitonic string solutions.Comment: 29 pages, v3: section 5 is rewritten and string solutions are found, v4: a new section on general covariance in loop spac

Combined EISCAT radar and optical multispectral and tomographic observations of black aurora

Black auroras are recognized as spatially well-defined regions within a uniform diffuse auroral background where the optical emission is significantly reduced. Black auroras typically appear post-magnetic midnight and during the substorm recovery phase, but not exclusively so. We report on the first combined multimonochromatic optical imaging, bistatic white-light TV recordings and incoherent scatter radar observations of black aurora by EISCAT of the phenomenon. From the relatively larger reduction in luminosity at 4278 Å than at 8446 Å we show that nonsheared black auroras are most probably not caused by downward directed electrical fields at low altitude. From the observations, we determine this by relating the height and intensity of the black aurora to precipitating particle energy within the surrounding background diffuse aurora. The observations are more consistent with an energy selective loss cone. Hence the mechanism causing black aurora is most probably active in the magnetosphere rather than close to Earth

A reparametrization invariant surface ordering

We introduce a notion of a non-Abelian loop gauge field defined on points in loop space. For this purpose we first find an infinite-dimensional tensor product representation of the Lie algebra which is particularly suited for fields on loop space. We define the non-Abelian Wilson surface as a `time' ordered exponential in terms of this loop gauge field and show that it is reparametrization invariant.Comment: 11 pages, clarifications and added ref

Camera calibration by an integrating sphere for the auroral tomography observation

Auroral tomography is a technique to reconstruct three-dimensional (3 D) luminous structure from multiple two-dimensional (2D) images of aurora. The reconstructed auroral luminous structure can provide useful information such as altitude profiles and vortex configuration. In order to obtain the absolute volume emission rate of the aurora distribution, it is essential to have the absolute sensitivity calibration of imaging by formulating the relation between pixel values and absolute brightness of corresponding direction of each pixel. The relation between pixel value and brightness is formulated and calculated from the absolute sensitivity calibration. We took the flat-field images of the integrating sphere calibration standard at National Institute of Polar Research using one camera system, which was installed at Merasjarvi (one of the ALIS observing site, ALIS is the acronym of Auroral Large Imaging System, which is a multi-station ground-based optical observing network). National Institute of Polar Research, Japan and Swedish Institute of Space Physics in Kiruna, Sweden have carried out collaborative observations for auroral tomography under ALIS. The sensitivity calibration result is applied to the reconstruction of volume emission rate distribution from the tomographic images observed by ALIS on March 1, 1998

Constraining Maximally Supersymmetric Membrane Actions

We study the recent construction of maximally supersymmetric field theory Lagrangians in three spacetime dimensions that are based on algebras with a triple product. Assuming that the algebra has a positive definite metric compatible with the triple product, we prove that the only non-trivial examples are either the well known case based on a four dimensional algebra or direct sums thereof.Comment: 11 pages, very minor changes. Reference added. Version to be published in JHE