Presentasjon av masteroppgave: Magnus Fagernes Ivarsen
Distinguishing screening mechanisms with environment-dependent velocity statistics
Alternative theories of gravity typically invoke an environment-dependent screening mechanism to allow phenomenologically interesting deviations from general relativity (GR) to manifest on larger scales, while reducing to GR on small scales. The observation of the transition from screened to unscreened behavior would be compelling evidence for beyond-GR physics. In this thesis, I show that pairwise peculiar velocity statistics – in particular the relative radial velocity dispersion, σ ǁ ˉ can be used to observe this transition when they are binned by some measure of halo environment. I establish this by measuring the radial velocity dispersion between pairs of halos in N-body simulations for three f(R) gravity and four Symmetron models. I bin the results in halo mass, ambient density, and the isolatedness of halos. Ambient density is found to be the most relevant measure of environment; it is distinct from isolatedness, and correlates well with theoretical expectations for the Symmetron model. Binning σ ǁ in ambient density, I find a strong environment-dependent signature for the Symmetron models, with the velocities showing a clear transition from GR to non-GR behavior. No such transition is observed for f(R), as the relevant scales are deep in the unscreened regime. Observations of the relative radial velocity dispersion in forthcoming peculiar velocity surveys, if binned appropriately by environment, therefore offer a valuable way of detecting the screening signature of modified gravity.
Veileder: Professor Per Barth Lilje, Institutt for teoretisk astrofysikk, UiO
Medveileder: Professor David F. Mota, Institutt for teroretisk astrofysikk, UiO
Intern sensor: Førsteamanuensis Boris Vilhelm Gudiksen, Institutt for teoretisk astrofysikk, UiO
Ekstern sensor: Post Doctoral Research Assistant Hans Arnold Winther, University of Oxford