Gauge Fixing Term: Physical Effects & Role in Spin Components

[Neitrino]

Hi...
Would you please advise me what does gauge fixing term do (physical point of view) ?

Does it eliminate unnecessary spin components from lagrangian for example:
Vector particle has two (massless case) or three (massive case) degrees of freedom.

Vector itself has four, and a vector (four component object) can handle spin-0 and spin 1 mode so adding a gauge fixing term does it project out spin-0 component ?

Or absence of spin-0 part is due to specific choice of kinetic term (F_mu_nu)...

Similarly in gravity... summetric tensor has 10 independent components and it can handle spin-0 spin-1 spin-2 modes... so does employment of harmonic gauge eliminate unnecessary modes or what role has it in this business?

Thanks

 

[muppet]

Hi neitrino,
The point of a gauge symmetry is that there's a redundancy in our description of the system; so physically, choosing a gauge is meaningless! The point is that you firstly have to choose some gauge, in order to actually write anything down at all, so you might as well pick one that makes the maths easy.
I can't say I'm familiar with harmonic gauge in GR, but having quickly looked it up the essential point seems to be the same; it doesn't alter the physical content of our statements, and it makes the maths easier in some problems- particularly when working in the weak-field approximation when we want to make contact between GR and Newtonian gravity.