Introduction to the Geometric Theory of Defects
  We describe defects - dislocations and disclinations - in the framework of Riemann-Cartan geometry. Curvature and torsion tensors are interpreted as surface densities of Frank and Burgers vectors, respectively. Equations of nonlinear elasticity theory are used to fix the coordinate system. The Lorentz gauge yields equations for the principal chiral SO(3)-field. In the absence of defects the geometric model reduces to the elasticity theory for the displacement vector field and to the principal chiral SO(3)-field model for the spin structure. 
M. O. Katanaev (Steklov Mathematical Institute, Moscow)