Dark energy survivals in massive gravity after GW170817: SO(3) invariant

Abstract

The recent detection of the gravitational wave signal GW170817 together with an electromagnetic counterpart GRB 170817A from the merger of two neutron stars puts a stringent bound on the tensor propagation speed. This constraint can be automatically satisfied in the framework of massive gravity. In this work we consider a general SO(3)-invariant massive gravity with five propagating degrees of freedom and derive the conditions for the absence of ghosts and Laplacian instabilities in the presence of a matter perfect fluid on the flat Friedmann-Lemaître-Robertson-Walker (FLRW) cosmological background. The graviton potential containing the dependence of three-dimensional metrics and a fiducial metric coupled to a temporal scalar field gives rise to a scenario of the late-time cosmic acceleration in which the dark energy equation of state wDE is equivalent to −1 or varies in time. We find that the deviation from the value wDE = −1 provides important contributions to the quantities associated with the stability conditions of tensor, vector, and scalar perturbations.In concrete models, we study the dynamics of dark energy arising from the graviton potential and show that there exist viable parameter spaces in which neither ghosts nor Laplacian instabilities are present for both wDE > −1 and wDE < −1. We also generally obtain the effective gravitational coupling G eff with non-relativistic matter as well as the gravitational slip parameter ηs associated with the observations of large-scale structures and weak lensing. We show that, apart from a specific case, the two quantities G eff and ηs are similar to those in general relativity for scalar perturbations deep inside the sound horizon.

Gravitational Rainbows: LIGO and Dark Energy at its Cutoff

“…SM is funded by the Imperial College President's Fellowship. ories of gravity-other models of dark energy, such as vector-tensor gravity or scalar-vector-tensor gravity, have also seen their parameter space remarkably affected (see however [13,14,44] for models that survive the bound). Lorentz-violating theories have also been profoundly constrained [45][46][47], although we shall focus on theories which are fundamentally LI here.…”

“…Last year, the first detection of GWs from a neutron star merger (GW170817), some 10 15 light seconds away, which arrived within one second of an optical counterpart (GRB170817A), allowed us to constrain the GW speed with remarkable precision [2-4]with c T the GW phase velocity and c γ the speed of light.Such a constraint has had far-reaching consequences for models of dark energy. Within the context of the Effective Field Theory (EFT) for dark energy [5], it was rapidly pointed out that (1) was sufficient to suppress the EFT operators that predict non-luminal gravitational propagation [6][7][8][9][10][11][12][13][14]. In particular, within the framework of scalar-tensor theories of gravity, Horndeski [15] has played a major part in the past decade as a consistent ghost-free EFT in which the scalar degree of freedom could play the role of dark energy.…”

Implications from GW170817 and I-Love-Q relations for relativistic hybrid stars

“…GW170817 placed constraints on the properties of the progenitor of the binary compact object GW170817 [28], and the GW background from compact binaries [29]. Moreover, GW170817 and GRB 170817A constrained the speed of gravity, the equivalence principle and Lorentz invariance [10], consequently constraining to a large degree gravity theories designed to explain the accelerated expansion of the Universe without dark energy [30][31][32][33][34][35][36][37] (see also [38,39] for earlier work). Furthermore, GW170817 furnished the first ever "standard siren" [40] measurement of the Hubble constant [19].…”

Neutron star merger GW170817 strongly constrains doubly coupled bigravity

“…Several high-precision large-scale structure surveys are planned to come into operation in the very near future, and therefore most attempts so far have focused on studying the cosmological implications of such theories in a hope that the future cosmological surveys will be sufficiently sensitive to judge against or for many of these theories. Notably, however, the recent detection of the GWs originating from a pair of merging neutron stars and the simultaneous detection of their electromagnetic counterpart, events GW170817 [81] and GRB 170817A [82], have proven to be able to provide us with an immense amount of knowledge about the landscape of the possible theories of gravity (mainly) through the strong bounds that they have placed on the speed of GWs [83][84][85][86][87][88][89][90][91][92][93][94][95][96][97][98][99][100] (see also Refs. [101][102][103][104][105] for discussions on the consequences of such strong bounds for classes of modified theories of gravity prior to the actual observations).…”