Eq. 9.124 has 3 steps. The first one gives 0 propagator for ε goes to 0. The final step, the one with Z gives infinity. Can anyone post the correct steps? Is there anything wrong in previews equations? It is important for me to learn the Ryder's book method. I have an exam in 10 days
what is meant by a particle should not overclose the univese? what is overclose? is it packed?
''The allowed axion mass range, bounded from below by the requirement
that axions should not overclose the universe and from above by accelerator searches
and stellar evolution.