Light cone gauge

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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.

[edit] Gauge theory

In gauge theory, light-cone gauge refers to the condition $A + = 0$ where

A + (x 0, x 1, x 2, x 3) = A 0 (x 0, x 1, x 2, x 3) + A 3 (x 0, x 1, x 2, x 3)

It is a method to get rid of the redundancies implied by Yang-Mills symmetry.

[edit] String theory

In string theory, light-cone gauge fixes the reparameterization invariance on the world sheet by

X + (σ,τ) = p + τ

where $p +$ is a constant and $τ$ is the worldsheet time.

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).