# Light cone gauge

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.

## 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.

## String theory

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

$X^{+}(\sigma ,\tau )=p^{+}\tau$

where $p^{+}$  is a constant and $\tau$  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).