15961894
Comparing selfinteracting scalar fields and R + R**3 cosmological models
We generalize the well-known analogies between m2φ2 and R + R2 theories to include the selfinteraction λφ4-term for the scalar field. It turns out to be the R + R3 Lagrangian which gives an appropiate model for it. Considering a spatially flat Friedman cosmological model, common and different properties of these models are discussed, e. g., by linearizing around a ground state the masses of the resp. spin 0-parts concide. Finally, we prove a general conformal equivalence theorem between a Lagrangian L = L(R), L′L″ ≠ 0, and a minimally coupled scalar field in a general potential.
123288737
On Static Asymptotically Flat Solutions of Fourth Order Gravitational Field Equations
It is shown that each non-flat regular static asymptotically flat solution of the gravitational field equation following from the Lagrangian 
 
 
 
 
 
 
has in a certain sense positive energy. Further, for a set of parameters including the BACH-EINSTEIN theory 
 
 
 
 
 
 
some results concerning the full nonlinear behaviour of the solutions of the field equation will be given. 
 
 
 
Uber statisch asymptotisch flache Losungen von Gravitationsfeldgleichungen vierter Ordnung 
 
 
 
Es wird gezeigt, das jede nicht-flache regulare statische asymptotisch flache Losung der Gravitationsfeldgleichung, die aus einem Lagrangeausdruck 
 
 
 
 
 
 
folgt, in einem gewissen Sinne positive Energie hat. Ferner wird fur eine bestimmte Parametermenge, die die BACH-EINSTEIN-Theorie 
 
 
 
 
 
 
enthalt, einiges uber das volle nichtlineare Verhalten der Losungen der Feldgleichung mitgeteilt.
17350104
Inhomogeneous Cosmological Models with Flat Slices Generated from the EINSTEIN‐DE SITTER Universe
A family of cosmological models in considered which in a certain synchronized system of reference possess flat slices t = const. They are generated from the EINSTEIN-DE SITTER universe by a suitable transformation. Under physically reasonable presumptions these transformed models fulfil certain energy conditions. 
 
 
 
Es wird eine Familie kosmologischer Modelle betrachtet, die in einemi gewissen synchronisierten Bezugssystem flache Schichten t = const. besitzen. Sie werden mittels einer geeigneten Transformation aus dem EINSTEIN-DE SITTER-Universum erzeugt. Diese transformierten Modelle erfullen unter physikalisch sinnvollen Voraussetzungen gewisse Energie bedingungen.
15300220
Exact Cosmological Solutions of Nonlinear F(R)-Gravity
We report on the cited papers refs. 1 - 18 from the following points of view: What do we exactly know about solutions when no exact solution (in the sense of "solution in closed form") is available? In which sense do these solutions possess a singularity? In which cases do conformal relations and/or dimensional reductions simplify the deduction? Furthermore, we outline some open questions worth of being studied in future research.
16873779
The massive scalar field in a closed Friedmann universe model - new rigorous results
For the minimally coupled scalar field in Einstein's theory of gravitation we look for the space of solutions within the class of closed Friedmann universe models. We prove D ≥ 1, where D ≥ is the dimension of the set of solutions which can be integrated up to t ∞ (D > 0 was conjectured by PAGE (1984)). We discuss concepts like “the probability of the appearance of a sufficiently long inflationary phase” and argue that it is primarily a probability measure μ in the space V of solutions (and not in the space of initial conditions) which has to be applied. μ is naturally defined for Bianchi-type I cosmological models because V is a compact cube. The problems with the closed Friedmann model (which led to controversial claims in the literature) will be shown to originate from the fact that V has a complicated non-compact non-Hausdorff Geroch topology: no natural definition of μ can be given. 
 
 
 
We conclude: the present state of our universe can be explained by models of the type discussed, but thereby the anthropic principle cannot be fully circumvented. 
 
 
 
Fur das minimal gekoppelte Skalarfeld in Einsteinscher Gravitationstheorie betrachten wir den Losungsraum in der Klasse der geschlossenen Friedmannmodelle des Universums. Wir beweisen, das D ≥ 1 gilt, wobei D die Dimension der Menge derjenigen Losungen ist, die sich bis t ∞ integrieren lassen. (D > 0 war von PAGE (1984) vermutet worden.) Wir diskutieren Begriffe wie, ”die Wahrscheinlichkeit des Auftretens einer hinreichend langen inflationaren Phase„ und argumentieren, das man primar ein Wahrscheinlichkeitsmas μ im Raum der Losungen V (und nicht im Raum der Anfangswerte) anwenden mus. Fur kosmologische Modelle vom Bianchi-Typ I gibt es eine naturliche Definition fur μ, da dort V ein kompakter Wurfel ist. Die Probleme mit dem geschlossenen Friedmannmodell (die zu Kontroversen in der Literatur fuhrten) ergeben sich aus der Tatsache, das V dort eine komplizierte Geroch-Topologie hat, die weder kompakt noch hausdorffsch ist, so das sich keine naturliche Definition fur μ angeben last. 
 
 
 
Wir schliesen: Zwar last sich der heutige Zustand unseres Universums durch Modelle des hier diskutierten Typs erklaren, jedoch last sich dabei das anthropische Prinzip nicht vollig umgehen.
14074913
4D wormhole with signature change in the presence of extra dimensions
A regular vacuum solution in 5D gravity on the principal bundle with the U(1) structural group is proposed as a 4D wormhole. This solution has two null hypersurfaces where an interchange of the sign of some 5D metric components happens. For a 4D observer living on the base of this principal bundle this is a wormhole with two asymptotically flat Lorentzian (Euclidean) spacetimes connected by a Euclidean (Lorentzian) throat. The 4D Lorentzian observer sees these two null hypersurfaces as electric charges.
31917251
On an algorithm solving two-level programming problems with nonunique lower level solutions
In the paper, an algorithm is presented for solving two-level programming problems. This algorithm combines a direction finding problem with a regularization of the lower level problem. The upper level objective function is included in the regularzation to yield uniqueness of the follower's solution set. This is possible if the problem functions are convex and the upper level objective function has a positive definite Hessian. The computation of a direction of descent and of the step size is discussed in more detail. Afterwards the convergence proof is given.Last but not least some remarks and examples describing the difficulty of the inclusion of upper-level constraints also depending on the variables of the lower level are added.
122589785
Models for Constrained Motion and d'Alembert's Principle
A theorem of Arnol'd and Gallavotti states that by a suitable potential of increasing rigidity a mechanical system with conservative forces can be constrained to a hypersurface of the configuration space and its motion approaches a solution of the reduced Lagrangian equation. In this paper the theorem will be generalized to time- and velocity-dependent forces including time-dependent constraints and proved with the aid of the method of averaging. This technique also allows us to identify the constraint force as the averaged negative gradient of the constraint potential.
117822141
Axiomatic Characterization of Physical Geometry
Operations with rigid bodies.- Regions and transport mappings.- The Helmhotz-Lie problem.- Characterization of Euclidean geometry.