Divergence of the $1/N_f$ series expansion in QED
  The perturbative expansion series in coupling constant in QED is divergent. It is either an asymptotic series or an arrangement of a conditionally convergent series. The sum of these types of series depends on the way we arrange partial sums for successive approximations. The $1/N_f$ series expansion, where $N_f$ is the number of flavours, defines a rearrangement of this series, and therefore, its convergence would serve as a proof that the perturbative series is, in fact, conditionallyconvergent.Unfortunately, the $1/N_f$ series also diverges.We proof this usingarguments similar to those of Dyson.   We expect that some of the ideas and techniques discussed in our paper will find some use in finding the true nature of the perturbative series in coupling constant as well as the $1/N_f$ expansion series. 
Mofazzal Azam