Symmetry breaking for bosonic systems on orbifolds

We discuss a general class of boundary conditions for bosons living in an extra spatial dimension compactified on S-1/Z(2). Discontinuities for both fields and their first derivatives are allowed at the orbifold fixed points. We analyze examples with free scalar fields and interacting gauge vector bosons, deriving the mass spectrum that depends on a combination of the twist and the jumps. We discuss how the same physical system can be characterized by different boundary conditions, related by local field redefinitions that turn a twist into a jump or vice versa. When the description is in term of discontinuous fields, appropriate lagrangian terms should be localized at the orbifold fixed points. (C) 2002 Elsevier Science (USA).