synthetic differential geometry
Introductions
from point-set topology to differentiable manifolds
geometry of physics: coordinate systems, smooth spaces, manifolds, smooth homotopy types, supergeometry
Differentials
Tangency
The magic algebraic facts
Theorems
Axiomatics
Models
differential equations, variational calculus
Chern-Weil theory, ∞-Chern-Weil theory
Cartan geometry (super, higher)
We state the definition below in Def. . First we need the following preliminaries:
Denote by the duplex (sometimes called paracomplex or hyperbolic) numbers, which is the associative algebra over the real numbers generated by the elements s.t. , in other words the real Clifford algebra . A PDE theory analogous to complex holomorphy may be developed based on this algebra; for a function (under an identification of with ), paracomplex linearity of means the real components of must satisfy the equations and . These are the hyperbolic analogue of the Cauchy-Riemann equations, although clearly not defining an elliptic system? since the components of therefore satisfy the wave equations . In the context of differential geometry over , such functions are sometimes called paraholomorphic.
As with CR geometry, one can study real hypersurfaces of manifolds carrying such hyperbolic structure (discussed below):
(HR manifold)
An HR manifold (for “hyperbolic-real”) is a differentiable manifold together with a sub-bundle of the hyperbolified tangent bundle, such that and , where is the bundle involution s.t. .
G-structures of this type only exist on even-dimensional differentiable manifolds, and have been known since the classical contributions of Libermann. Explicitly, an almost-hyperbolic structure on a real -manifold is determined by a reduction of the structure group , defining a bundle automorphism s.t. . Locally this means that , when integrable, is of the form:
on fibers, so that the transition functions of satisfy the wave equations just discussed. One can also give various integrability conditions of , although as a Dirac structure the simplest to state is the vanishing of the Nijenhuis tensor , a sign away from its complex analogue.
(…)
(…)
BR manifold?
The classical articles are:
P. Libermann, Sur le probleme d’equivalence de certaines structures infinitesimales, Ann. Mat. Pura Appl., 36 (1954), 27-120.
P. Libermann, Sur les structures presque paracomplexes, C.R. Acad. Sci. Paris, 234 (1952), 2517-2519.
A convenient modern survey appears in::
And a more recent article done in the style of generalized complex geometry is:
Last revised on March 14, 2019 at 08:09:31. See the history of this page for a list of all contributions to it.