Transitions of orbifold vacua

Abstract

Abstract We study the global structure of vacua of heterotic strings compactified on orbifolds T 4 /ℤ N (N = 2, 3) in the presence of heterotic 5-branes. Gauge symmetry breaking associated with orbifold is described by instantons in the field theory. There is phase transition between small (zero size limit) instantons and heterotic 5-branes. This mechanism provides top-down, stringy account to the spectrum and modular invariance condition of non-perturbative vacua with 5-branes. Also it takes us from one vacuum to another by emitting and absorbing instantons. This means that many vacua with different gauge theories are in fact connected and are inherited from perturbative vacua. It follows that there is also transition of twisted instantons at the fixed points. Thus we can understand transitions among perturbative vacua as well.