Standard Sirens as a Novel Probe of Dark Energy

Abstract

Cosmological models with a dynamical dark energy field typically lead to a modified propagation of gravitational waves via an effectively time-varying gravitational coupling G(t). The local variation of this coupling between the time of emission and detection can be probed with standard sirens. Here we discuss the role that Lunar Laser Ranging (LLR) and binary pulsar constraints play in the prospects of constraining G(t) with standard sirens. In particular, we argue that LLR constrains the matter-matter gravitational coupling G N (t), whereas binary pulsars and standard sirens constrain the quadratic kinetic gravity self-interaction G gw (t). Generically, these two couplings could be different in alternative cosmological models, in which case LLR constraints are irrelevant for standard sirens. We use the Hulse-Taylor pulsar data and show that observations are highly insensitive to time variations of G gw (t), and we thus conclude that future gravitational waves data will become the best probe to test G gw (t), and will hence provide novel constraints on dynamical dark energy models.Introduction.-Gravitational waves (GW) are a longstanding prediction of Einstein's theory of general relativity (GR) and their recent direct detection by the LIGO/Virgo collaboration [1] has confirmed many aspects of GR [2-4] while future tests will offer exciting opportunities to probe the Universe and its constituents even further. In particular, the unknown nature of dark energy -the component driving the observed late-time accelerated expansion of the Universe [5]has motivated a number of alternative models that promote the cosmological constant of the standard ΛCDM model to be a dynamical dark energy field (see e.g. [6][7][8][9][10]). GW will provide important constraints for cosmology via standard sirens (multi-messenger detections of GW and electromagentic signals [11]), as they can test the properties of these dynamical dark energy fields as well as provide independent constraints on cosmological parameters such as the current expansion rate of the universe, H 0 , whose current observational constraints exhibit a 4-6σ tension (see review in [12]). In the upcoming years, detectors such as KAGRA [13], , the ET [15] and LISA [16] (and possible proposed detectors such as DECIGO [17]) will come online to measure GW with more precision and over cosmological distances.One notable non-trivial signature that can be probed with standard sirens is the possibility of a time-varying gravitational coupling G(t), which typically arises in dynamical dark energy models. In this case, the quadratic action for GW that propagate at the speed of light on a cosmological background is typically given by:

Measurements of H0 in modified gravity theories: The role of lensed quasars in the late-time Universe

“…It has been argued and explored that information from gravitational wave (GW) observations, in particular measures on the propagation speed of GWs, can strongly discriminate among possible extensions of GR. See Refs [24][25][26][27][28]. for discussions in this regard.…”

Weighing massive neutron star with screening gravity: a look on PSR J0740 + 6620 and GW190814 secondary component

“…Chameleon theories in principle has already this physical characteristic and this constraints does not affect in general any aspect in these theories. The authors in [70] calculate that the effects of a plausible variation in G N on the period decay of a local binary system are many orders of magnitude suppressed with respect to the effects of a change in G N . As a result,Ġ N /G N is constrained to ∼ 10 −3 , while G N is unconstrained by observations of the binary orbital decay rate.…”

Cosmological constraints on dark energy in light of gravitational wave bounds

“…In addition, GW 'standard siren' tests will become a powerful probe of the conformal G 4 (φ )R coupling in (8), which is the main driver of the surviving Horndeski-related deviations from GR discussed and constrained throughout this paper -for related discussions see e.g. [26,27,[103][104][105][106][107][108][109][110][111][112]. Ultimately a holistic analysis, combining constraints from several regimes and using a range of techniques stretching from observational astrophysics to particle theory, will be essential in acquiring the best possible understanding of the dynamics underlying the accelerated expansion of the late universe.…”