At this point the only term which contains ξ ξ is the term containing ∂ ∂ μ μ ξ ξ + e A μ μ . But the dependence on ξ ξ can be gauged away by the gauge transformation which sends A μ μ + 1 e ∂ ∂ μ μ ξ ξ ↦ ↦ A μ μ . This is known as the unitary or unitarity gauge. In differential-geometric language, as is spelled out in the following box, the condensate ξ ξ ( x ) has defined a canonical trivialization.