15665320
On the history of fourth order metric theories of gravitation
We present the history of fourth order metric theories of gravitation from its beginning in 1918 until 1988.
119455132
$\Delta-$String: A Hybrid Between Einstein's and String Paradigmes
Superthin and superlong solutions in 5D Kaluza-Klein gravity are considered. It is shown that they can be cosidered as a hybrid between Einstein's and string paradigmes.
7357148
Cosmic strings and strings in gravitational waves
We consider strings with the Nambu action as extremal surfaces in a given space-time, thus, we ignore their back reaction. Especially, we look for strings sharing one symmetry with the underlying space-time. If this is a non-null symmetry the problem of determining ihc motion of the string can be dimensionally reduced. We get exact solutions for the following cases: straight and circle-like strings in a Friedmann background, straight strings in an anisotropic Kasner background, different types of strings in the metric of a gravitational wave. The solutions will be discussed. 
 
 
 
Wir betrachten Strings mit der Nambu-Wirkung als Extremalflachen in einer gegebenen Raum-Zeit, d. h., wir ignorieren ihre Ruckwirkung. Wir interessieren uns dabei besonders fur solche Strings, die eine Isometrie mit der unterliegenden Raum-Zeit gemeinsam haben. Handelt es sich dabei um eine nicht-lichtartige Symmetrie, so las Bt sich das Problem der Bestimmung der Stringbewegung dimensionsreduzieren. Wir erhalten exakte Losungen fur die folgenden Falle: gerade und kreisrunde Strings im Friedmann-Hintergrund, gerade Strings im anisotropen Kasner-Hintergrund sowie verschiedene Stringtypen in der Metrik einer Gravitationswelle. Die Losungen werden diskutiert.
1345747
Inhomogeneous Cosmological Models Containing Homogeneous Inner Hypersurface Geometry. Changes of the BIANCHI Type.
There are investigated such cosmological models which instead of the usual spatial homogeneity property only fulfil the condition that in a certain synchronized system of reference all spacelike sections t = const. are homogeneous manifolds. This allows time-dependent changes of the BIANCHI type. Discussing differential-geometrical theorems it is shown which of them are permitted. Besides the trivial case of changing into type I there exist some possible changes between other types. However, physical reasons like energy inequalities partially exclude them. 
 
 
 
Es werden kosmologische Modelle betrachtet, die anstelle der ublichen raumlichen Homogenitatseigenschaft nur die Bedingung erfullen, das in einem gewissen synchronisierten Bezugssystem alle Raumschnitte t = const. homogene Mannigfaltigkeiten sind. Neben dem trivialen Fall des Wechsels zu Typ I gibt es einige mogliche Anderungen zwischen anderen Typen. Physikalische Grunde wie Energieungleichungen schliesen diese jedoch teilweise aus.
122236194
The Singularity Problem of Gravitation
We review the present status of the singularity problem in gravitation theory. First we repeat the known results for Einstein's theory. After this, different other gravitation theories are considered under the following aspect: Which of the presumptions leading to singularities in Einstein's theory are not fulfilled, and can this prevent the singularities? In detail: scalar matter fields do not fulfil the positive energy condition, bimetric theories change the gravitational vacuum, theories with torsion and fourth order gravity add new geometric terms. It turns out that the answer is never simply no or yes, but requires new conditions, and new types of singularities occur. Otherwise there exist essential situations where the alternative theories satisfactorily prevent the singular behaviour known from Einstein's theory. Finally, we review on chaotic singularities.
15973668
On static spherical symmetric solutions of the Bach‐Einstein gravitational field equations
For field equations of 4th order, follwing from a Lagrangian “Ricci scalar plus Weyl scalar”, it is shown (using methods of non-standard analysis) that in a neighbourhood of Minkowski space there do not exist regular static spherically symmetric solutions. With that (besides the known local expansions about r = o nad r = ∞ resp.) for the first time a global statement on the existence of such solutions is given. Finally, this result will be discussed in connection with Einstein's particle programme. 
 
 
 
Fur die Feldgleichungen 4. Ordnung, die aus einem Lagrangeausdruck „Ricci-Skalar plus Weyl-Skalar” folgen, wird unter Zuhilfenahme von Methoden der Nicht-Standard-Analysis gezeigt, das in einer Umgebung des Minkowskiraumes keine statischen kugeslymmetrischen Losungen existeieren. Damit wird erstmals neben den bekannten lokalen Entwicklungen um r = o und r = ∞ eine globale Aussage uber die Existenz solcher Losungen getroffen. Anschliesend wird dies Ergebnis im Zusammenhang mit Einstein's Teilchenprogramm diskutiert.
16037187
A measurement of the charge asymmetry of hadronic events in electron positron annihilation
AbstractThe quark charge asymmetry, summed over flavours, has been measured at centre of mass energies of 35 GeV and 44 GeV using the JADE detector sited on the electron-positron storage ring PETRA. The asymmetry is found to be consistent with the expectations of the standard model at both energies and enables a measurement of the product of the axial-vector coupling constant of the electron with the axial-vector coupling constants of the quarks, assuming the moduli of these latter to be flavour independent. This gives, with reasonable assumptions concerning the effects of
$$B^0 \overline {B^0 } $$
 mixing,aeaq=−1.09±0.18±0.23 where the first error is statistical and the second systematic.