# Gauge fixing in 5D vs 4D, and photon polarization

1. Aug 11, 2009

### kuon

I'm sorry if what I say is not right, or I haven't understood it right,

- In 3+1 D we have the photon with spin 1 => it has two polarizations.

Our Gauge field $$A_\mu$$ has 4 components => We have two extra degrees of freedom. => We need to get rid of the extra 2 fixing the gauge.

1. The Lorentz gauge is not enough to fix them. What else can we do?

- In 4+1 D we have the photon with spin 1=> it has two polarizations.

Our Gauge field $$A_\mu$$ has 5 components => We have THREE extra degrees of freedom. => We need to get rid of the extra 3 fixing the gauge.

2. The Lorentz gauge is not enough to fix them. What else can we do?

Thank you very much for your attention :)

2. Aug 11, 2009

### Bob_for_short

In the Lorentz gauge there are two extra degrees of freedom which do not contribute even without getting rid of them. They cannot exchange the energy-momentum with physical degrees of freedom.