Quick question regarding superficial degrees of freedom and Ward identities.
For instance in Peskin and Schroeder it is stated that the photon-self energy is superficially quadratically UV divergent but due to the Ward identity it is only logarithmically divergent. I don't see this argument.
The self-energy is given by
How does the Ward identity, or in other words, gauge invariance kill of the divergences?
A friendly helper
This post imported from StackExchange Physics at 2014-04-15 16:38 (UCT), posted by SE-user A friendly helper