Testing Screened Fifth Forces: From Cosmological to Solar System Scales

Dombrowski, Johannes David (2021) Testing Screened Fifth Forces: From Cosmological to Solar System Scales. PhD thesis, University of Nottingham.

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In this thesis we present three different approaches to testing screened fifth forces on scales ranging from the largest structures in the Universe to the Solar System.

Firstly, we study the cosmic matter bispectrum in a cubic Galileon model and find that the shape dependence of Vainshtein screening leaves a very intuitive signature on the bispectrum. A numerical analysis with hi_class demonstrates that the strength of the signal relative to the signal from general relativity alone is proportional to the fractional energy density of the Galileon at redshift z=0 and evolves like a^(3/2). Since this shape dependence is very characteristic of Vainshtein screening, it may prove useful for differentiating between different models of fifth forces with data from future galaxy surveys.

Second, we determine the conditions under which the solar-system constraints on the time evolution of the gravitational constant may be extrapolated to cosmological scales. If these conditions are met for a specific fifth force model, strong constraints on the evolution of the cosmological gravitational constant are placed, which prohibit self acceleration as an explanation for the accelerated expansion of the late Universe. We find that the conditions hold for the most common screening mechanisms unless the screening is extreme in the sense that even the largest and least dense observable objects in the Universe are screened, in which case violations of the equivalence principle may prohibit the extrapolation of solar-system constraints to cosmological scales.

Lastly, we derive an analytic solution for the Galileon field in a hierarchical two-body system, where one mass greatly exceeds the other mass. We observe that the field around the smaller mass becomes elliptical outside the `Vainshtein boundary'. We estimate that this ellipticity only has a small effect in the sun-earth system, but could be at the ~4% level on intergalactic scales and thus influence the dynamics of field galaxies moving through the field of a distant galaxy cluster in a manner significantly different from the predictions of pure general relativity.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Burrage, Clare
Avgoustidis, Anastasios
Keywords: Modified Gravity, Cosmology, Screening Mechanisms, Large-Scale Structures
Subjects: Q Science > QB Astronomy
Faculties/Schools: UK Campuses > Faculty of Science > School of Physics and Astronomy
Item ID: 65942
Depositing User: Dombrowski, Johannes
Date Deposited: 31 Dec 2021 04:40
Last Modified: 31 Dec 2021 04:40
URI: http://eprints.nottingham.ac.uk/id/eprint/65942

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