Cosmological constraints on dark energy in light of gravitational wave bounds

Abstract

Gravitational wave (GW) constraints have recently been used to significantly restrict models of dark energy and modified gravity. New bounds arising from GW decay and GW-induced dark energy instabilities are particularly powerful in this context, complementing bounds from the observed speed of GWs. We discuss the associated linear cosmology for Horndeski gravity models surviving these combined bounds and compute the corresponding cosmological parameter constraints, using CMB, redshift space distortion, matter power spectrum and BAO measurements from the Planck, SDSS/BOSS and 6dF surveys. The surviving theories are strongly constrained, tightening previous bounds on cosmological deviations from ΛCDM by over an order of magnitude. We also comment on general cosmological stability constraints and the nature of screening for the surviving theories, pointing out that a raised strong coupling scale can ensure compatibility with gravitational wave constraints, while maintaining a functional Vainshtein screening mechanism on solar system scales. Finally, we discuss the quasi-static limit as well as (constraints on) related observables for near-future surveys.

Degeneracy, matter coupling, and disformal transformations in scalar-tensor theories

“…The current and main application of DHOST theories is to address cosmic acceleration, however, similar to vanilla scalar-tensor theories, one can consider many noncosmological applications and our analysis will apply there as well. Nonetheless, it is an intriguing question whether our results can potentially complement the existing constraints on such cosmological applications, in particular the recent results on the decay of gravitational waves into dark energy [80], on the destabilization of dark energy inhomogeneities by gravitational waves [81], and on the Vainshtein screening mechanism [32] (see also [31,[82][83][84] and below for other related works). At present these results are quite orthogonal to our work given that the exotic types of matter that we have so far identified as problematic do not play any role in these analyses.…”

“…It is actually instructive to compare the two approaches, so in the following we perform a canonical analysis of our toy model, which we hope will clarify the argument by removing the added complications related to general covariance and local Lorentz invariance that we had to deal with before. To this end we first write the action (83) in first-order form with the help of a new variable ψ and a Lagrange multiplier λ, both being bosonic (i.e., Grassmanneven)…”

Searching for modified gravity in the astrophysical gravitational wave background: Application to ground-based interferometers

“…We can note that these bounds are of the accuracy matching the current measures [94][95][96]. Thus, we can expect that future constraints using real data from a possible AGWB in this band will impose strong limits on possible deviations from general relativity.…”

On the road to per cent accuracy IV: ReACT – computing the non-linear power spectrum beyond ΛCDM

“…Various alternatives to these assumptions have been proposed, coming in the form of dynamical dark energy (for reviews see Copeland et al 2006;Li et al 2011) and modifications to gravity (MG) (for reviews see Clifton et al 2012;Joyce et al 2016;Koyama 2018). Despite the vast theoretical space which has been developed, much of this has been very well constrained by cosmological observations (for a review of recent constraints see Ferreira 2019;Huterer & Shafer 2018;Noller 2020).…”