T2: Behaviour of pertubation and loops

Question 1

Define regularisation for a divergent feynman diagram

Answer 1

Introducing a cuttoff Λ&raquo_space; m into the momentum integral of the loop, truncating to before infinity.

Question 2

Define renormalisation

Answer 2

We redefine mass in the denominator of the expression for the Feynman propagator by combining

m_r^2 = m^2 + G_F^0(0)

Question 3

Give the form of G_0^F (x,y) in momentum space

Answer 3

INT d^4p /(2π)^4 -i/p^2 + m^2