Ultrafast carrier dynamics investigated by a novel pump-and-probe-terahertz technique

In dieser Arbeit wird eine neuartige Methode, die so genannte "Pump-and-Probe-THz-" Technik zur Untersuchung der Ladungsträgerdynamik in dem Halbleiter GaAs und dem Hochtemperatursupraleiter YBa2Cu3O7-x (YBCO) vorgeschlagen. Hierbei wird THz-Strahlung von der zu untersuchenden Probe emittiert. Diese wird zusätzlich durch einen Pumplaserpuls beeinflusst und zeitlich aufgelöst gemessen. Es wird gezeigt, dass sich mit dieser Methode Ladungsträger-Relaxationszeiten im GaAs in ihrer Abhängigkeit vom äußeren elektrischen Feld, der Ladungsträgerdichte und dem Ladungsträgereinfang in lokalisierten Zuständen im Inneren der Energielücke, bestimmen lassen. Im Fall des YBCO kann die Relaxationsrate der Quasiteilchen und die Rekombinationszeit der Cooperpaare im supraleitenden Zustand bestimmt werden und somit der Einfluss verschiedener Streumechanismen in Abhängigkeit von der Temperatur unterhalb TC

Color Variability of the Blazar AO 0235+16

Multicolor (UBVRIJHK) observations of the blazar AO 0235+16 are analyzed. The light curves were compiled at the Turin Observatory from literature data and the results of observations obtained in the framework of the WEBT program (http://www.to.astro/blazars/webt/). The color variability of the blazar was studied in eight time intervals with a sufficient number of multicolor optical observations; JHK data are available for only one of these. The spectral energy distribution (SED) of the variable component remained constant within each interval, but varied strongly from one interval to another. After correction for dust absorption, the SED can be represented by a power law in all cases, providing evidence for a synchrotron nature of the variable component. We show that the variability at both optical and IR wavelengths is associated with the same variable source.Comment: 11 pages, 9 figures, 4 tables, accepted for publication in Astronomy Report

On massive spin 2 interactions

In this paper we use a constructive approach based on gauge invariant description of massive high spin particles for investigation of possible interactions of massive spin 2 particle. We work with general case of massive spin 2 particle living in constant curvature $(A)dS_d$ background, which allows us carefully consider all flat space, massless or partially massless limits. In the linear approximation (cubic terms with no more than two derivatives in the Lagrangians and linear terms with no more than one derivative in gauge transformations) we investigate possible self-interaction, interaction with matter (i.e. spin 0, 1 and 1/2 particles) and interaction with gravity.Comment: 26 pages, LaTeX 2e, some comments and new references adde

On the existence of Killing vector fields

In covariant metric theories of coupled gravity-matter systems the necessary and sufficient conditions ensuring the existence of a Killing vector field are investigated. It is shown that the symmetries of initial data sets are preserved by the evolution of hyperbolic systems.Comment: 9 pages, no figure, to appear in Class. Quant. Gra

Uniqueness Theorem of Static Degenerate and Non-degenerate Charged Black Holes in Higher Dimensions

We prove the uniqueness theorem for static higher dimensional charged black holes spacetime containing an asymptotically flat spacelike hypersurface with compact interior and with both degenerate and non-degenerate components of the event horizon.Comment: 9 pages, RevTex, to be published in Phys.Rev.D1

Exact Solutions for the Intrinsic Geometry of Black Hole Coalescence

We describe the null geometry of a multiple black hole event horizon in terms of a conformal rescaling of a flat space null hypersurface. For the prolate spheroidal case, we show that the method reproduces the pair-of-pants shaped horizon found in the numerical simulation of the head-on-collision of black holes. For the oblate case, it reproduces the initially toroidal event horizon found in the numerical simulation of collapse of a rotating cluster. The analytic nature of the approach makes further conclusions possible, such as a bearing on the hoop conjecture. From a time reversed point of view, the approach yields a description of the past event horizon of a fissioning white hole, which can be used as null data for the characteristic evolution of the exterior space-time.Comment: 21 pages, 6 figures, revtex, to appear in Phys. Rev.

Symmetries of spacetime and their relation to initial value problems

We consider covariant metric theories of coupled gravity-matter systems satisfying the following two conditions: First, it is assumed that, by a hyperbolic reduction process, a system of first order symmetric hyperbolic partial differential equations can be deduced from the matter field equations. Second, gravity is supposed to be coupled to the matter fields by requiring that the Ricci tensor is a smooth function of the basic matter field variables and the metric. It is shown then that the ``time'' evolution of these type of gravity-matter systems preserves the symmetries of initial data specifications.Comment: 12 pages, to appear in Class. Quant. Gra

Dynamical extensions for shell-crossing singularities

We derive global weak solutions of Einstein's equations for spherically symmetric dust-filled space-times which admit shell-crossing singularities. In the marginally bound case, the solutions are weak solutions of a conservation law. In the non-marginally bound case, the equations are solved in a generalized sense involving metric functions of bounded variation. The solutions are not unique to the future of the shell-crossing singularity, which is replaced by a shock wave in the present treatment; the metric is bounded but not continuous.Comment: 14 pages, 1 figur

Time-Independent Gravitational Fields

This article reviews, from a global point of view, rigorous results on time independent spacetimes. Throughout attention is confined to isolated bodies at rest or in uniform rotation in an otherwise empty universe. The discussion starts from first principles and is, as much as possible, self-contained.Comment: 47 pages, LaTeX, uses Springer cl2emult styl

On massive spin 2 electromagnetic interactions

In this paper we investigate electromagnetic interactions for massive spin 2 particles in (A)dS space at linear approximation using gauge invariant description for such massive particles. We follow bottom-up approach, i.e. we begin with the introduction of minimal interaction and then proceed by adding non-minimal interactions with higher and higher number of derivatives together with corresponding non-minimal corrections to gauge transformations until we are able to restore gauge invariance broken by transition to gauge covariant derivatives. We manage to construct a model that smoothly interpolates between massless particle in (A)dS space and massive one in a flat Minkowski space. Also we reproduce the same results in a frame-like formalism which can be more suitable for generalizations on higher spins.Comment: 24 pages, no figures. Clarifications and references added. Version to appear in Nucl. Phys.