Left-right symmetric theories and vacuum domain walls and strings

Abstract

Theories in which a discrete left-right symmetry is spontaneously broken are expected to lead to the formation of vacuum domain walls. Although the existence of such walls at the present epoch is observationally excluded, we show that such theories are allowed if the discrete symmetry is embedded in a larger continuous symmetry, e.g., SO(10), spontaneously broken at higher temperatures. In this case vacuum strings are formed when the larger symmetry is broken, and these become connected by domain walls when the discrete symmetry is broken. The bounded domain walls tend to shrink, and the system of strings and domain walls decays before its energy density becomes comparable to that of matter. In particular, our arguments allow the symmetry breaking pattern SO(10) → … S[O(6)×O(4)] → SU(3)×SU(2)×U(1) which has been proposed by others.