# I $k^0-\bar{k^0}$ mixing and gauge boson propagator

1. Jan 23, 2017

### Monaliza Smile

Hi all ,

I'm studying $k^0-\bar{k^0}$ mixing from Cheng & Li's book "gauge_theory_of_elementary_particle_physics", page: 379 , I found that they consider the gauge boson propagator in the Feynman gauge, where
$i\Delta_{\mu\nu} = -i \frac{g_{\mu\nu}}{k^2-M^2_W}$ , but till my knowledge in this gauge the goldstone bosons remain in the theory, so why the contribution of the charged goldstone bosons for instance has not been taken into account in these calculation of the box diagram of $k^0-\bar{k^0}$ like $W^\pm$ ?

2. Feb 12, 2017