Group theoretical approach to quantum fields in de Sitter space I. The principal series

Using unitary irreducible representations of the de Sitter group, we construct the Fock space of a massive free scalar field. In this approach, the vacuum is the unique dS invariant state. The quantum field is a posteriori defined by an operator subject to covariant transformations under the dS isometry group. This insures that it obeys canonical commutation relations, up to an overall factor which should not vanish as it fixes the value of hbar. However, contrary to what is obtained for the Poincare group, the covariance condition leaves an arbitrariness in the definition of the field. This arbitrariness allows to recover the amplitudes governing spontaneous pair creation processes, as well as the class of alpha vacua obtained in the usual field theoretical approach. The two approaches can be formally related by introducing a squeezing operator which acts on the state in the field theoretical description and on the operator in the present treatment. The choice of the different dS invariant schemes (different alpha vacua) is here posed in very simple terms: it is related to a first order differential equation which is singular on the horizon and whose general solution is therefore characterized by the amplitude on either side of the horizon. Our algebraic approach offers a new method to define quantum field theory on some deformations of dS space.Comment: 35 pages, 2 figures ; Corrected typo, Changed referenc

Kompetenznetz E-Learning Hessen

Mit dem Kompetenznetz e-learning-hessen.de vernetzen sich die hessischen Hochschulen mit Hilfe der Koordination und Unterstützung durch das httc und Förderung durch das Hessische Ministerium für Wissenschaft und Kunst rund um das Thema E-Learning. Dieser Beitrag beschreibt die Ziele des Netzwerks, dessen Maßnahmen und Elemente und die bisherigen Erfahrungen und seine Entwicklung seit dem Jahr 2000. Mit der abschließenden Bewertung werden Anhaltspunkte für eine erfolgreiche Vernetzung von Hochschulen und ein Ausblick auf die geplanten Aktivitäten des hessischen Netzwerkes in den nächsten Jahren gegeben. (DIPF/ Orig.

CPVMatch - Concentrating photovoltaic modules using advanced technologies and cells for highest efficiencies

This paper presents the project Concentrating Photovoltaic modules using advanced technologies and cells for highest efficiencies (CPVMatch), which is funded from the European Union’s Horizon 2020 research and innovation programme. V multi-junction solar cells and CPV modules. Concerning cells, novel wafer bonded four-junction solar cells made of GaInP/GaAs//GaInAs/Ge are optimized with the target of reaching 48% efficiency under concentration at the end of the project. Moreover, multi-junction solar cell technologies with advanced materials - like ternary IV element mixtures (i.e. SiGeSn) and nanostructured anti-reflective coatings - are investigated. Concerning CPV modules the project focuses on both Fresnel-based and mirror-based technologies with a target efficiency of 40% under high concentrations beyond 800x. Achromatic Fresnel lenses for improved light management without secondary optics are investigated. In addition, smart, mirror-based HCPV modules are developed, which include a new mirror-based design, the integration of high efficiency, low cost DC/DC converters and an intelligent tracking sensor (PSD sensor) at module level. A profound life-cycle and environmental assessment and the development of adapted characterization methods of new multi-junction cells and HCPV modules complete the work plan of CPVMatch

Systematic effects in the extraction of the 'WMAP haze'

The extraction of a 'haze' from the WMAP microwave skymaps is based on subtraction of known foregrounds, viz. free-free (bremsstrahlung), thermal dust and synchrotron, each traced by other skymaps. While the 408 MHz all-sky survey is used for the synchrotron template, the WMAP bands are at tens of GHz where the spatial distribution of the radiating cosmic ray electrons ought to be quite different because of the energy-dependence of their diffusion in the Galaxy. The systematic uncertainty this introduces in the residual skymap is comparable to the claimed haze and can, for certain source distributions, have a very similar spectrum and latitudinal profile and even a somewhat similar morphology. Hence caution must be exercised in interpreting the 'haze' as a physical signature of, e.g., dark matter annihilation in the Galactic centre.Comment: 17 pages, 12 figures; improved diffusion model; extended discussion of spectral index maps; clarifying comments, figures and references added; to appear in JCA