  We demonstrate the optomechanical cooling of a tapered optical nanofiber by
coupling the polarization of light to the mechanical angular momentum of the
system. The coupling is enabled by birefringence in the fiber and does not make
use of an optical resonator. We find evidence for cooling in the distribution
of thermally driven amplitude fluctuations and the noise spectrum of the
torsional modes. Our proof-of-principle demonstration shows cavity-less cooling
of the torsional degree of freedom of a macroscopically extended nanofiber.
