1. H.X. Chen, W. Chen, X. Liu, S.L. Zhu, Phys. Rep. 639, 1 (2016)
2. F.K. Guo, C. Hanhart, U.G. Meissner, Q. Wang, Q. Zhao, B.S. Zou, arXiv:1705.00141 [hep-ph]
3. M. Karliner, J.L. Rosner, T. Skwarnicki, arXiv:1711.10626 [hep-ph]
4. L. Roca, E. Oset, Phys. Rev. D 82, 054013 (2010)
5. J. Yamagata-Sekihara, L. Roca, E. Oset, Phys. Rev. D 82, 094017 (2010). Erratum: [Phys. Rev. D 85, 119905 (2012)]