Lorenz gauge condition

In electromagnetism, the Lorenz gauge or Lorenz gauge condition is a partial gauge fixing of the electromagnetic vector potential. The condition is that ${\displaystyle \partial _{\mu }A^{\mu }=0}$. This does not completely fix the gauge: one can still make a gauge transformation ${\displaystyle A^{\mu }\to A^{\mu }+\partial ^{\mu }f}$ where ${\displaystyle f}$ is a harmonic scalar function (that is, a scalar function satisfying ${\displaystyle \partial _{\mu }\partial ^{\mu }f=0}$, the equation of a massless scalar field).

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