When I read paper PRB89, 235431 about the effective field theory of graphene, there is a statement that QED perturbative series is only asymptotic and eventually diverges at very high orders (e. g. the second paragraph in sec. II), which I cannot understand exactly.
It is known that QED is renormalizable. Thus, why the perturbative series diverge at the orders higher than 137. Please give me some refs, thank you.
