Vacuum Manifold

Please note that the content of this book primarily consists of articles
available from Wikipedia or other free sources online. In quantum field
theory, the vacuum state may be degenerate. Each pure vacuum state
generates its own superselection sector. The space of all pure vacuum
states often has a manifold structure and is called the vacuum manifold.
Vacuum manifolds arise during the process of spontaneous symmetry
breaking from a group G to a subgroup H and the corresponding vacuum
manifold has to be a realization of G and contain the quotient space
G/H. In many cases, it would simply be G/H, although it could be larger.