Action of fields on captive disclination loops.

We report on two effects observed in experiments with captive disclination loops on polymeric fibers immersed in nematics and submitted to electric and/or magnetic fields. We show that the magnetic field oblique to a fiber with axial or helicoidal anchoring on its surface induces translation of disclination loops. Fields orthogonal to fibers with helicoidal anchoring make disclination loops rotate around the field direction. In the linear regime of this last chirogyral effect, the angle of rotation is proportional to the helix wave vector and its sense unveils the chirality of the helix. We propose a model explaining the origin and all features of these two effects.