Perturbative unitarity and NEC violation in genesis cosmology

• DOI: 10.1007/jhep10(2022)140
• Publication Date: 2022-10-21T14:07:55Z
• Authors: Yong Cai; Ji Xu; Shuai Zhao; Siyi Zhou
• Keywords: High Energy Physics - Theory; Violations; Astrophysics and Astronomy; Spacetime singularities; and Gravity; Spacetime Singularities; Cosmology and Nongalactic Astrophysics (astro-ph.CO); Gravity; Quantum physics; FOS: Physical sciences; QC770-798; General Relativity and Quantum Cosmology (gr-qc); 01 natural sciences; General Relativity and Quantum Cosmology; Gravitational waves; Relativity theory; Relativity; Spacetime; High Energy Physics - Phenomenology (hep-ph); Universe; Nuclear and particle physics. Atomic energy. Radioactivity; 0103 physical sciences; Field theory; String theory; Cosmic microwave background temperature; Physics; Classical theories of gravity; Elementary particles; Cosmology; Elementary Particles and Fields and String Theory; High Energy Physics - Phenomenology; High Energy Physics - Theory (hep-th); Quantum field theories; Singularities; Classical Theories of Gravity; Astrophysics - Cosmology and Nongalactic Astrophysics

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.