Journal of High Energy Physics
Explorations of the violation of null energy condition (NEC) in cosmology could enrich our understanding of the very early universe and the related gravity theories. Although a fully stable NEC violation can be realized in the “beyond Horndeski” theory, it remains an open question whether a violation of the NEC is allowed by some fundamental properties of UV-complete theories or the consistency requirements of effective field theory (EFT). We investigate the tree-level perturbative unitarity for stable NEC violations in the contexts of both Galileon and “beyond Horndeski” genesis cosmology, in which the universe is asymptotically Minkowskian in the past. We find that the constraints of perturbative unitarity imply that we may need some unknown new physics below the cut-off scale of the EFT other than that represented by the “beyond Horndeski” operators.
© 2022 The Authors
This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (CC-BY 4.0), which permits any use, distribution and reproduction in any medium, provided the original author(s) and source are credited.
Original Publication Citation
Cai, Y., Xu, J., Zhao, S., & Zhou, S. (2022). Perturbative unitarity and NEC violation in genesis cosmology. Journal of High Energy Physics, 2022(10), 1-28. https://doi.org/10.1007/JHEP10(2022)140
Cai, Yong; Xu, Ji; Zhao, Shuai; and Zhou, Siyi, "Perturbative Unitarity and NEC Violation in Genesis Cosmology" (2022). Physics Faculty Publications. 697.