Perturbative unitarity and NEC violation in genesis cosmology
Abstract
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.
Keywords
Cite
@article{arxiv.2207.11772,
title = {Perturbative unitarity and NEC violation in genesis cosmology},
author = {Yong Cai and Ji Xu and Shuai Zhao and Siyi Zhou},
journal= {arXiv preprint arXiv:2207.11772},
year = {2022}
}
Comments
32 pages, 5 figures; updated to match the published version