BPS surface observables in six-dimensional (2,0) theory

The supergroup OSp(8*|4), which is the superconformal group of (2,0) theory in six dimensions, is broken to the subgroup OSp(4|2)xOSp(4|2) by demanding the invariance of a certain product in a superspace with eight bosonic and four fermionic dimensions. We show that this is consistent with the symmetry breaking induced by the presence of a flat two-dimensional BPS surface in the usual (2,0) superspace, which has six bosonic and sixteen fermionic dimensions.Comment: 9 pages, LaTeX. v2: reference adde

Manifest superconformal covariance in six-dimensional (2,0) theory

A superconformal generalization of Dirac's formalism for manifest conformal covariance is presented and applied to the free (2,0) tensor multiplet field theory in six dimensions. A graded symmetric superfield, defined on a supercone in a higher-dimensional superspace is introduced. This superfield transforms linearly under the transformations of the supergroup OSp(8*|4), which is the superconformal group of the six-dimensional (2,0) theory. We find the relationship between the new superfield and the conventional (2,0) superfields in six dimensions and show that the implied superconformal transformation laws are correct. Finally, we present a manifestly conformally covariant constraint on the supercone, which reduces to the ordinary differential constraint for the superfields in the six-dimensional space-time.Comment: 12 pages, LaTeX. v2: minor clarification adde

Supersymmetric coupling of a self-dual string to a (2,0) tensor multiplet background

We construct an interaction between a (2,0) tensor multiplet in six dimensions and a self-dual string. The interaction is a sum of a Nambu-Goto term, with the tension of the string given by the modulus of the scalar fields of the tensor multiplet, and a non-local Wess-Zumino term, that encodes the electromagnetic coupling of the string to the two-form gauge field of the tensor multiplet. The interaction is invariant under global (2,0) supersymmetry, modulo the equations of motion of a free tensor multiplet. It is also invariant under a local fermionic kappa-symmetry, as required by the BPS-property of the string.Comment: 12 pages, LaTe

Energy radiated from a fluctuating selfdual string

We compute the energy that is radiated from a fluctuating selfdual string in the large $N$ limit of $A_{N-1}$ theory using the AdS-CFT correspondence. We find that the radiated energy is given by a non-local expression integrated over the string world-sheet. We also make the corresponding computation for a charged string in six-dimensional classical electrodynamics, thereby generalizing the Larmor formula for the radiated energy from an accelerated point particle.Comment: 12 page

Free tensor multiplets and strings in spontaneously broken six-dimensional (2,0) theory

We first review the representations of the six-dimensional (2,0) superalgebra on a free tensor multiplet and on a free string. We then construct a supersymmetric Lagrangian describing a free tensor multiplet. (It also includes a decoupled anti self-dual part of the three-form field strength.) This field theory is then rewritten in variables appropriate for analyzing a situation where the R-symmetry is spontaneously broken by the vacuum expectation values of the scalar moduli fields. Finally, we construct a supersymmetric and kappa-symmetric action for a free string.Comment: 15 pages, LaTe

Classical self-dual strings in d=6, (2,0) theory from afar

We show how one can get solitonic strings in a six-dimensional (2,0) supersymmetric theory by incorporating a nonlinear interaction term. We derive a zero force condition between parallel strings, and compute a metric on a moduli space which is $R^4$ when the strings are far apart. When compactifying the strings on a two-torus we show that, in the limit of vanishing two-torus, one regains the moduli space of two widely separated dyons of equal magnetic charges in four dimensions.Comment: 13 pages, clarifications and added reference

Thomson scattering of chiral tensors and scalars against a self-dual string

We give a non-technical outline of a program to study the (2,0) theories in six space-time dimensions. Away from the origin of their moduli space, these theories describe the interactions of tensor multiplets and self-dual spinning strings. We argue that if the ratio between the square of the energy of a process and the string tension is taken to be small, it should be possible to study the dynamics of such a system perturbatively in this parameter. As a first step in this direction, we perform a classical computation of the amplitude for scattering chiral tensor and scalar fields (i.e. the bosonic part of a tensor multiplet) against a self-dual spinnless string.Comment: 24 pages, LaTeX, 2 figures. v2: added discussion on supersymmetry in Ch.

Rolling Bearings Lubricated With Refrigerant

Oil-free systems gain increased popularity in the chiller industry. This technology is often related to reduced maintenance, higher system efficiency and smaller environmental footprint. In refrigeration compressors which use oil for the lubrication it is impossible to avoid mixing of refrigerant and oil in the system. The system efficiency is affected by the contamination of the refrigerant by oil. One possibility to operate a compressor of a chiller without oil is the pure refrigerant lubrication (PRL) bearing technology. With this technology the traditional oil lubrication system can be removed completely and the bearings are lubricated only with refrigerant. This removes the challenges related to mixtures of fluids - on the chiller performance side (efficiency reduction due to oil contamination of the working fluid) as well as on the lubrication side (lubricant diluted by refrigerant). The challenge which pure refrigerant lubrication poses to rolling bearings was overcome by a special bearing development. Energy efficiency and total cost of ownership are major drivers of the industry. Therefore, accurate predictions of bearing power losses became a fundamental component of the bearing performance rating. For bearings operating in refrigerant environment, friction is even more important, since the heat generation affects the thermodynamics of the refrigerant, and can lead to refrigerant evaporation and starvation. A special bearing test rig has been developed, which allows the investigation of the bearing performance under pure refrigerant lubrication conditions. Its main components are the hermetic bearing test head and the refrigerant supply system. The test rig was designed to withstand the conditions present in refrigerant environments and enables the investigation of refrigerant condition and injection properties of typical bearing operating conditions. The refrigerant is pumped, filtered and conditioned in the lubrication circuit before it is injected into the bearing to provide cooling and lubrication. The bearings inside the stainless steel housing can be subjected to various loads and rotational speeds. The refrigerant properties such as film building ability, density and the boundary friction coefficient as well as possible evaporation influence the bearing friction characteristics. With the test rig the influence of the thermodynamic behaviour can be analysed. The mapping of the friction behaviour under various operating conditions allows the optimisation of the injection properties. PRL bearings enable machine designs which offer excellent overall system efficiency

Sequential and Spontaneous Star Formation Around the Mid-Infrared Halo HII Region KR 140

We use 2MASS and MSX infrared observations, along with new molecular line (CO) observations, to examine the distribution of young stellar objects (YSOs) in the molecular cloud surrounding the halo HII region KR 140 in order to determine if the ongoing star-formation activity in this region is dominated by sequential star formation within the photodissociation region (PDR) surrounding the HII region. We find that KR 140 has an extensive population of YSOs that have spontaneously formed due to processes not related to the expansion of the HII region. Much of the YSO population in the molecular cloud is concentrated along a dense filamentary molecular structure, traced by C18O, that has not been erased by the formation of the exciting O star. Some of the previously observed submillimetre clumps surrounding the HII region are shown to be sites of recent intermediate and low-mass star formation while other massive starless clumps clearly associated with the PDR may be the next sites of sequential star formation.Comment: Accepted for publication in MNRAS, 8 pages, 10 figure