paper

Fifth force constraints from the separation of galaxy mass components

arXiv:1807.01482 · doi:10.1103/PhysRevD.98.064015

Abstract

One of the most common consequences of extensions to the standard models of particle physics or cosmology is the emergence of a fifth force. While generic fifth forces are tightly constrained at Solar System scales and below, they may escape detection by means of a screening mechanism which effectively removes them in dense environments. We constrain the strength and range of a chameleon- or symmetron-screened fifth force with Yukawa coupling -- as well as an unscreened fifth force with differential coupling to galactic mass components -- by searching for the displacement it predicts between galaxies' stellar and gas mass centroids. Taking data from the Alfalfa HI survey, identifying galaxies' gravitational environments with the maps of Desmond et al. (2018a) and forward-modelling with a Bayesian likelihood framework, we find evidence for at Mpc, with at maximum-likelihood. A similar fifth-force model without screening gives no increase in likelihood over the case for any . Although we validate these results by several methods, we do not claim screened modified gravity to provide the only possible explanation for the signal: this would require knowing that "galaxy formation" physics could not be responsible. We show also the results of a more conservative -- though less well motivated -- noise model which yields only upper limits on , ranging from for Mpc to at Mpc. We show how these constraints may be improved by future galaxy surveys and identify the key features of an observational programme for directly constraining fifth forces on galactic scales. This paper provides a complete description of the analysis summarised in Desmond et al. (2018b).

29 pages, 16 figures; minor revision to match PRD published version

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