Mechanism by which a symmetry intrinsic to the Lagrangian is apparently broken. The break occurs seemingly when the system is viewed in its ground state (lowest energy state), which does not necessarily share the same symmetry as the Lagrangian.
If we assume some symmetry applies to the , then we face two possibilities: either the ground state of our theory is non-degenerate or it is degenerate.
- If non-degenerate, then there is only one ground state, which also shares the same symmetry as .
- If degenerate, then there are multiple states that minimise . We can select any one of these states arbitrarily, but none of these states share the symmetry of .