Clear and Measurable Signature of Modified Gravity in the Galaxy Velocity Field

Abstract

Reprinted with permission from the American Physical Society: Physical Review Letters 112, 22, 221102 c 2014 by the American Physical Society. Readers may view, browse, and/or download material for temporary copying purposes only, provided these uses are for noncommercial personal purposes. Except as provided by law, this material may not be further reproduced, distributed, transmitted, modied, adapted, performed, displayed, published, or sold in whole or part, without prior written permission from the American Physical Society.Additional information: Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. The velocity field of dark matter and galaxies reflects the continued action of gravity throughout cosmic history. We show that the low-order moments of the pairwise velocity distribution v 12 are a powerful diagnostic of the laws of gravity on cosmological scales. In particular, the projected line-of-sight galaxy pairwise velocity dispersion σ 12 ðrÞ is very sensitive to the presence of modified gravity. Using a set of high-resolution N-body simulations, we compute the pairwise velocity distribution and its projected line-of-sight dispersion for a class of modified gravity theories: the chameleon fðRÞ gravity and Galileon gravity (cubic and quartic). The velocities of dark matter halos with a wide range of masses would exhibit deviations from general relativity at the ð5-10Þσ level. We examine strategies for detecting these deviations in galaxy redshift and peculiar velocity surveys. If detected, this signature would be a "smoking gun" for modified gravity.

Testing the quasi-static approximation inf(R) gravity simulations

“…3 shows that the enhancement of ∆P θθ /P θθ for these models relative to ΛCDM is a lot stronger than that in the matter power spectra -to almost an order of magnitude in the case of F6. This reiterates the aforementioned advantage of using the velocity divergence power spectrum as a more sensitive probe of modified gravity [26]. Just as in the case of the matter power spectrum, there does not seem to be any significant difference in the enhancements when including time derivatives, as both the non-static and quasi-static simulations of the three models seem to be well-converged.…”

The Vainshtein mechanism in the cosmic web

“…This suggests that probing galactic halos well beyond their virial radii, out to their caustic-crossing or turn-around radii, is more likely to pick up differences between LCDM and models with a Vainshtein screening mechanism (see also [51][52][53][54]). …”

First experimental constraints on the disformally coupled Galileon model

“…The galaxy velocity field could also be a decisive probe to test modified gravity theories, as advocated in (Zu 2013;Hellwing et al 2014). However, this probe would require to have a correct modelling of the Galileon model nonlinearities.…”