title: Clear and measurable signature of modified gravity in the galaxy velocity field.
abstract: 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}(r) 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 f(R) 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 (5-10)σ 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.
authors.affiliation: Institute for Computational Cosmology, Department of Physics, Durham University, South Road, Durham DH1 3LE, United Kingdom and Interdisciplinary Centre for Mathematical and Computational Modelling (ICM), University of Warsaw, ul. Pawińskiego 5a, Warsaw, Poland.
authors.forename: Wojciech A
authors.initials: WA
authors.lastname: Hellwing
authors.affiliation: Institute for Computational Cosmology, Department of Physics, Durham University, South Road, Durham DH1 3LE, United Kingdom and Institute for Particle Physics Phenomenology, Department of Physics, Durham University, Durham DH1 3LE, United Kingdom.
authors.forename: Alexandre
authors.initials: A
authors.lastname: Barreira
authors.affiliation: Institute for Computational Cosmology, Department of Physics, Durham University, South Road, Durham DH1 3LE, United Kingdom.
authors.forename: Carlos S
authors.initials: CS
authors.lastname: Frenk
authors.affiliation: Institute for Computational Cosmology, Department of Physics, Durham University, South Road, Durham DH1 3LE, United Kingdom.
authors.forename: Baojiu
authors.initials: B
authors.lastname: Li
authors.affiliation: Institute for Computational Cosmology, Department of Physics, Durham University, South Road, Durham DH1 3LE, United Kingdom.
authors.forename: Shaun
authors.initials: S
authors.lastname: Cole