For loop integrals in QFT, B actually has a pole for relevant values of a , b and d . For example in scalar ϕ ϕ 4 theory in 4 dimensions, the loop integral in the calculation of one-loop renormalization of the interaction vertex has ( a , b , d ) = ( 0 , 2 , 4 ) . We use the 'trick' of dimensional regularization, analytically continuing d to d = 4 − − ϵ ϵ with ϵ ϵ a small parameter.