1. R. Essig et al., Working Group Report: New Light Weakly Coupled Particles, in proceedings of the Community Summer Study 2013: Snowmass on the Mississippi, Minneapolis, MN, U.S.A., 29 July–6 August 2013, arXiv:1311.0029 [INSPIRE].
2. J. Alexander et al., Proceedings of the Dark Sectors 2016 Workshop: Community Report, Menlo Park, California, U.S.A., 28–30 April 2016, arXiv:1608.08632 [INSPIRE].
3. M. Battaglieri et al., U.S. Cosmic Visions: New Ideas in Dark Matter 2017: Community Report, in proceedings of the U.S. Cosmic Visions: New Ideas in Dark Matter, College Park, MD, U.S.A., 23–25 March 2017, arXiv:1707.04591 [INSPIRE].
4. J. Beacham et al., Physics Beyond Colliders at CERN: Beyond the Standard Model Working Group Report, J. Phys. G 47 (2020) 010501 [arXiv:1901.09966] [INSPIRE].
5. B.W. Lee and S. Weinberg, Cosmological Lower Bound on Heavy Neutrino Masses, Phys. Rev. Lett. 39 (1977) 165 [INSPIRE].