Backlund transformations and knots of constant torsion

The Backlund transformation for pseudospherical surfaces, which is equivalent to that of the sine-Gordon equation, can be restricted to give a transformation on space curves that preserves constant torsion. We study its effects on closed curves (in particular, elastic rods) that generate multiphase solutions for the vortex filament flow (also known as the Localized Induction Equation). In doing so, we obtain analytic constant-torsion representatives for a large number of knot types.Comment: AMSTeX, 29 pages, 5 Postscript figures, uses BoxedEPSF.tex (all necessary files are included in backlund.tar.gz