  The key feature of Weyl semimetals (WSM) is the presence of topologically
protected Dirac cones in a 3D material. We consider the effect of restricting
geometry on the spectrum of excitations in WSM using as a model a cylindrical
WSM wire. For the full manifold of hard boundary conditions, we derive the
general form of the dispersion equation relating the energy of the excitations
and their momentum along the wire. We show that only the special class of
boundary conditions, corresponding to decoupled helicities or, equivalently, to
pinned directions of the electron spin on the surface, support massless
excitations. For a general boundary condition, these excitations acquire mass
inversely proportional to the radius of the wire. This demonstrates that
boundary phenomena may play a crucial role in formation of excitations in WSM
based structures.
