Rigid particle revisited: extrinsic curvature yields the Dirac equation

We reexamine the model of relativistic particle with higher-derivative term linear on the first extrinsic curvature (rigidity). The passage from classical to quantum theory requires a number of rather unexpected steps which we report here. We found that, contrary to common opinion, quantization of the model in terms of $so(3.2)$-algebra yields massive Dirac equation.