Beyond the growth rate of cosmic structure: Testing modified gravity models with an extra degree of freedom

Burrage, Clare; Parkinson, David; Seery, David

Abstract

© 2017 American Physical Society. In "modified" gravity the observed acceleration of the universe is explained by changing the gravitational force law or the number of degrees of freedom in the gravitational sector. Both possibilities can be tested by measurements of cosmological structure formation. In this paper we elaborate the details of such tests using the Galileon model as a case study. We pay attention to the possibility that each new degree of freedom may have stochastically independent initial conditions, generating different types of potential well in the early universe and breaking complete correlation between density and velocity power spectra. This "stochastic bias" can confuse schemes to parametrize the predictions of modified gravity models, such as the use of the growth parameter f alone. Using data from the WiggleZ Dark Energy Survey we show that it will be possible to obtain constraints using information about the cosmological-scale force law embedded in the multipole power spectra of redshift-space distortions. As an example, we obtain an upper limit on the strength of the conformal coupling to matter in the cubic Galileon model, giving |1/M|200/MP. This allows the fifth-force to be stronger than gravity, but is consistent with zero coupling.

Citation

Burrage, C., Parkinson, D., & Seery, D. (2017). Beyond the growth rate of cosmic structure: Testing modified gravity models with an extra degree of freedom. Physical Review D, 96(4), Article 043509. https://doi.org/10.1103/PhysRevD.96.043509

• Journal Article Type: Article
• Acceptance Date: Mar 1, 2017
• Online Publication Date: Aug 11, 2017
• Publication Date: Aug 15, 2017
• Deposit Date: Oct 17, 2017
• Publicly Available Date: Oct 17, 2017
• Journal: Physical Review D
• Print ISSN: 2470-0010
• Electronic ISSN: 2470-0029
• Publisher: American Physical Society
• Peer Reviewed: Peer Reviewed
• Volume: 96
• Issue: 4
• Article Number: 043509
• DOI: https://doi.org/10.1103/PhysRevD.96.043509
• Public URL: https://nottingham-repository.worktribe.com/output/877929
• Publisher URL: https://journals.aps.org/prd/abstract/10.1103/PhysRevD.96.043509
• Additional Information: Burrage, Clare, Parkinson, David and Seery, David. Beyond the growth rate of cosmic structure: Testing modified gravity models with an extra degree of freedom; Phys. Rev. D 96, 043509.