  The breaking of symmetry is the ground on which many physical phenomena are
explained. This is important in particular for bipartite lattice structure as
graphene and carbon nanotubes, where particle-hole and pseudo-spin are relevant
symmetries. Here we investigate the role played by the defect-induced breaking
of these symmetries in the electronic scattering properties of armchair
single-walled carbon nanotubes. From Fourier transform of the local density of
states we show that the active electron scattering channels depend on the
conservation of the pseudo-spin. Further, we show that the lack of
particle-hole symmetry is responsible for the pseudo-spin selection rules
observed in several experiments. This symmetry breaking arises from the lattice
reconstruction appearing at defect sites. Our analysis gives an intuitive way
to understand the scattering properties of carbon nanotubes, and can be
employed for newly interpret several experiments on this subject. Further, it
can be used to design devices such as pseudo-spin filter by opportune defect
engineering.
