How important is $i\epsilon$ in QFT?

@article{Fariborz2015HowII,
  title={How important is \$i\epsilon\$ in QFT?},
  author={Amir H. Fariborz and Renata Jora and Joseph Schechter},
  journal={arXiv: High Energy Physics - Phenomenology},
  year={2015}
}
We discuss the role of $i\epsilon$ in quantum field theories and suggest that it can be identified with the dimensional regularization parameter $i\epsilon=4-d$ thus clarifying and simplifying issues related to the infrared divergences without altering any of the present knowledge in QFT. We further present the relevance of this assumption for the optical theorem. 

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