100 research outputs found
Causal geometries and third-order ordinary differential equations
We discuss contact invariant structures on the space of solutions of a
third-order ordinary differential equation. Associated to any third-order
differential equation modulo contact transformations, Chern introduced a
degenerate conformal Lorentzian metric on the space of 2-jets of functions of
one variable. When the Wuenschmann invariant vanishes, the degenerate metric
descends to a proper conformal Lorentzian metric on the space of solutions. In
the general case, when the Wuenschmann invariant is not zero, we define the
notion of a causal geometry, and show that the space of solutions supports one.
The Wuenschmann invariant is then related to the projective curvature of the
indicatrix curve cut out by the causal geometry in the projective tangent
space. When the Wuenschmann vanishes, the causal structure is then precisely
the sheaf of null geodesics of the Chern conformal structure. We then introduce
a Lagrangian and associated Hamiltonian from which the degenerate conformal
Lorentzian metric are constructed. Finally, necessary and sufficient conditions
are given for a rank three degenerate conformal Lorentzian metric in four
dimensions to correspond to a third-order differential equation
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