Boundary Structure and Module Decomposition of the Bosonic Z2 Orbifold Models with R2=1/2 k

Abstract

The Z 2 bosonic orbifold models with compactification radius R 2=1/2 k are examined in the presence of boundaries. Demanding the extended algebra characters to have definite conformal dimension and to consist of an integer sum of Virasoro characters, one arrives at the right splitting of the partition function. This is used to derive a free field representation of a complete, consistent set of boundary states, compatible with the modular transformations of the characters. Finally the modules of the extended symmetry algebra that correspond to the finitely many characters are identified inside the direct sum of Fock modules that constitute the space of states of the theory.