  The catalysis of chiral symmetry breaking by an applied constant magnetic
field and in the presence of boundaries along third axis is investigated in the
four-dimensional Nambu-Jona-Lasinio model. It is shown that in case of periodic
boundary conditions for fermions the magnetic field breaks the chiral symmetry,
generating a dynamical mass even at the weakest attractive interaction between
fermions. For antiperiodic boundary conditions the effect of the finite third
dimension is to counteract the chiral symmetry breaking.

High Energy Physics - Phenomenology;Condensed Matter;High Energy Physics - Theory