2018/07/31 by Eugeny Babichev, Sabir Ramazanov, Alexander Vikman · 2 citations
Physics and Astronomy · #Black Holes and Theoretical Physics #Classical mechanics #Cosmology and Gravitation Theories #Dispersion relation #Galaxies: Formation, Evolution, Phenomena #Instability #Mathematical physics #Physics #Quantum electrodynamics #Quantum mechanics #Scalar (mathematics) #Scalar field #Superluminal motion #Tachyon #astro-ph.CO #gr-qc #hep-ph #hep-th
paper · pdf · doi:10.1088/1475-7516/2018/11/023
published as JCAP11(2018)023 · 16 pages+appendices, references added, matches the published version
openalex created_date 2018/08/03 · openalex publication_date 2018/11/16 · arxiv created 2018/11/20 · arxiv updated 2018/11/21 · openalex updated_date 2026/08/06
We study the correspondence between models of a self-interacting canonical complex scalar field and P ( X )-theories/shift-symmetric k-essence. Both describe the same background cosmological dynamics, provided that the amplitude of the complex scalar is frozen modulo the Hubble drag. We compare perturbations in these two theories on top of a fixed cosmological background. The dispersion relation for the complex scalar has two branches. In the small momentum limit, one of these branches coincides with the dispersion relation of the P ( X )-theory. Hence, the low momentum phase velocity agrees with the sound speed in the corresponding P ( X )-theory. The behavior of high frequency modes associated with the second branch of the dispersion relation depends on the value of the sound speed. In the subluminal case, the second branch has a mass gap. On the contrary, in the superluminal case, this branch is vulnerable to a tachyonic instability. We also discuss the special case of the P ( X )-theories with an imaginary sound speed leading to the catastrophic gradient instability. The complex field models provide with a cutoff on the momenta involved in the instability.