Hello

Can anyone give me some ideas about my question?

In QED when we studied the self-energy tensor of photons the denominator of the integration which was witten

d=2pmpn+pmqn+pnqm-gmn(m2-p2-p.q) (1)

After the substitution

Ka=pa+(1-x)qa (*)

the result was written as

d=(2KmKn+2x(1-x)qmqn-gmn(m2-K2-x(1-x)q2)) (2)

but in my calculations I got eq(2) with extra parts so

how can i derive eq(2) from eq(1) by using eq(*) ?

p: is the four-momentum running through the lower half.

q: external four-momentum.

gmn: Minkowski metric.