Generalized Lorentz transformations

A real representation of Dirac algebra, using η=diag(−1,1,1,1) as standard metric is discussed. Among other interesting properties it allows to define a generalization of Lorentz transformations. Ordinary boosts and rotations are subsets The additional transformations are shown to describe transformations to displaced systems, rotating systems, “charged systems”, and others. Poincaré transformations are shown to be approximations of these generalized Lorentz transformations. Appendix D gives an interpretation. Ubi materia, ibi geometria (Johannes Kepler)     

Structure equations and constraint manifolds on Lorentz plane

Calculating the structure equation of a chain is important to represent the position of the end link on the chain. Furthermore, the structure equation helps to determine the constraint manifold of the chain. The constraint manifold satisfies to make geometric interpretations about the form that is obtained. What is more, the constraint forced on the positions of the end link by the rest of the chain is represented by the manifold. In Lorentz space, the structure equations change according to the causal characters of the first link. In this paper, we attain the structure equations of a planar open chain in terms of the causal character of the first link in this space. Later, the constraint manifolds of the chain by using these equations are given. Some geometric comments about these manifolds are explained.     

An observation about a theorem of A. D. Alexandrov concerning Lorentz transformations

By a theorem of A. D. Alexandrov a bijection : R _n ⁿ Rⁿ (n3) satisfiyng d(a,b)=0d ((a),(b))=0 a, b Rⁿ (d distance associated to the Minkowski metric) is a Lorentz transformation up to a dilatation. We prove that the inverse implication in the condition above may be dropped, being a consequence of the direct one.Dedicated to Raphael Artzy on the occasion of his 70^th birthday     

A characterization of Möbius transformations

Let be an integer and let be a domain of . Let be an injective mapping which takes hyperspheres whose interior is contained in to hyperspheres in . Then is the restriction of a Möbius transformation.

     

A characterization of semisimple plane polynomial automorphisms

It is well-known that an element of the linear group is semisimple if and only if its conjugacy class is Zariski closed. The aim of this paper is to show that the same result holds for the group of complex plane polynomial automorphisms.     

Elementary transformations of pfaffian representations of plane curves

Let C be a smooth curve in P² given by an equation F=0 of degree d. In this paper we consider elementary transformations of linear pfaffian representations of C. Elementary transformations can be interpreted as actions on a rank 2 vector bundle on C with canonical determinant and no sections, which corresponds to the cokernel of a pfaffian representation. Every two pfaffian representations of C can be bridged by a finite sequence of elementary transformations. Pfaffian representations and elementary transformations are constructed explicitly. For a smooth quartic, applications to Aronhold bundles and theta characteristics are given.     

A characterization of Hering's plane of order 27

Hering's translation plane of order 27 has been characterized by its order and the fact that it admits SL(2, 13) in its translation complement (see [1]). We show that, aside from the Desarguian plane and a Generalized, André plane, it is the only plane of order 27 which admits a subgroup of SL(2, 13) of order 13×12.Partially supported by FONDECYT 0343 and ANDES FOUNDATION.     

A characterization of ovoidal quadrics by plane sections

In [11], J. TITS characterized ovoidal quadrics of n-dimensional projective spaces (n N, n 3) by considering sections of planes passing through a fixed point of an ovoid. We want to show that a corresponding result is true if the set of planes under consideration is restricted to n-2 bundles of planes and one further plane, where this further plane may not be omitted. Moreover, our considerations will include the cases of infinite dimension.Dedicated to Professor Helmut Karzel on the occasion of his 60th birthday     

On birational transformations of pairs in the complex plane

This article deals with the study of the birational transformations of the projective complex plane which leave invariant an irreducible algebraic curve. We try to describe the state of the art and provide some new results on this subject.      

Differential transformations of parabolic second-order operators in the plane

Darboux’s classical results about transformations of second-order hyperbolic equations by means of differential substitutions are extended to the case of parabolic equations of the form Lu = (D _x ² + a(x, y)D _x + b(x, y)D _y + c(x, y))u = 0. We prove a general theorem that provides a way to determine admissible differential substitutions for such parabolic equations. It turns out that higher order transforming operators can always be represented as a composition of first-order operators that define a series of consecutive transformations. The existence of inverse transformations imposes some differential constrains on the coefficients of the initial operator. We show that these constraints may imply famous integrable equations, in particular, the Boussinesq equation.