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

Burrage, Clare, Parkinson, David and Seery, David (2017) Beyond the growth rate of cosmic structure: testing modified gravity models with an extra degree of freedom. Physical Review D, 96 (4). ISSN 2470-0010

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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/M_P. This allows the fifth-force to be stronger than gravity, but is consistent with zero coupling.

Item Type: Article
Schools and Departments: School of Mathematical and Physical Sciences > Physics and Astronomy
Research Centres and Groups: Astronomy Centre
Subjects: Q Science > QB Astronomy > QB0980 Cosmogony. Cosmology
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Depositing User: David Seery
Date Deposited: 31 May 2017 13:50
Last Modified: 02 Jul 2019 17:00

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Project NameSussex Project NumberFunderFunder Ref
Astrophysics and Cosmology - Sussex Consolidated GrantG1291STFC-SCIENCE AND TECHNOLOGY FACILITIES COUNCILST/L000652/1