Nonlocal Galileons and self-acceleration

Abstract

A certain class of nonlocal theories eliminates an arbitrary cosmological constant (CC) from a universe that can be perceived as our world. Dark energy then cannot be explained by a CC; it could however be due to massive gravity. We calculate the new corrections, which originate from the nonlocal terms that eliminate the CC, to the decoupling limit Lagrangian of massive gravity. The new nonlocal terms also have internal field space Galilean symmetry and are referred here as "nonlocal Galileons." We then study a self-accelerated solution and show that the new nonlocal terms change the perturbative stability analysis. In particular, small fluctuations are now stable and non-superluminal for some simple parameter choices, whereas for the same choices the pure massive gravity fluctuations are unstable. We also study stable spherically symmetric solutions on this background.

Newtonian approximation and possible time-varying G in nonlocal gravities

“…For this theory, [9][10][11][12][13][14][15][16] gave detailed cosmological perturbation analysis, and performed parameter constraints using observational data, including SNIa, BAO, CMB and structure formation data. There are some other nonlocal theories that perform well in cosmology, such as nonlocal Gauss-Bonnet gravity [17,18], the theory that includes tensor nonlocalities [19][20][21][22], nonlocal Galileons [23], the RT model of nonlocal gravity [24], the double-metric nonlocal gravity [25], and the double nonlocal gravity [26]. The above results indicate that it is not difficult to explain the late-time acceleration by nonlocal gravity.…”

Dark energy and inflation with a volume normalized action

“…This CC-free framework then necessitates a dynamical dark energy component that drives the accelerated expansion today. In this regard, [7] utilizes massive gravity [8,9], which is ghost free [10][11][12][13] and has a technically natural graviton mass [14]; it also presents a new class of healthy self-accelerated background solutions in the decoupling limit. With the help of nonlocal Galileon terms [15], these solutions exhibit no linear scalar-tensor mixing [16] and thus no van Dam-Veltman-Zakharov discontinuity [17,18].…”