Walls bounded by strings

Abstract

Extended structures consisting of walls bounded by strings appear in some unified gauge theories. The Spin(10) grand-unified-theory model provides the simplest example, provided the symmetry breaking proceeds via SU(4)\ifmmode\times\else\texttimes\fi{}SU(2)\ifmmode\times\else\texttimes\fi{}SU(2). It is shown that the presence of such structures may cause conflict with standard cosmology.