Generalized disformal Horndeski theories: Cosmological perturbations and consistent matter coupling
Abstract
Invertible disformal transformations are a useful tool to investigate ghost-free scalar-tensor theories. By performing a higher-derivative generalization of the invertible disformal transformation on Horndeski theories, we construct a novel class of ghost-free scalar-tensor theories, which we dub generalized disformal Horndeski theories. Specifically, these theories lie beyond the quadratic/cubic DHOST class. We explore cosmological perturbations to identify a subclass where gravitational waves propagate at the speed of light and clarify the conditions for the absence of ghost/gradient instabilities for tensor and scalar perturbations. We also investigate the conditions under which a matter field can be consistently coupled to these theories without introducing unwanted extra degrees of freedom.
- Publication:
-
Progress of Theoretical and Experimental Physics
- Pub Date:
- January 2023
- DOI:
- 10.1093/ptep/ptac161
- arXiv:
- arXiv:2209.02176
- Bibcode:
- 2023PTEP.2023a3E01T
- Keywords:
-
- General Relativity and Quantum Cosmology;
- Astrophysics - Cosmology and Nongalactic Astrophysics;
- High Energy Physics - Theory
- E-Print:
- 23 pages, 2 figures