In theoretical physics, light cone gauge is an approach to remove the ambiguities arising from a gauge symmetry. While the term refers to several situations, a null component of a field A is set to zero (or a simple function of other variables) in all cases.
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Gauge theory
In gauge theory, light-cone gauge refers to the condition
It is a method to get rid of the redundancies implied by Yang–Mills symmetry.
String theory
In string theory, light-cone gauge fixes the reparameterization invariance on the world sheet by
where
The advantage of light-cone gauge is that all ghosts and other unphysical degrees of freedom can be eliminated. The disadvantage is that some symmetries such as Lorentz symmetry become obscured (they become non-manifest, i.e. hard to prove).