Parametrizations for tests of gravity

Abstract

With the increasing wealth of high-quality astronomical and cosmological data and the manifold departures from General Relativity in principle conceivable, the development of generalized parameterization frameworks that unify gravitational models and cover a wide range of length scales and a variety of observational probes to enable systematic high-precision tests of gravity has been a stimulus for intensive research. A review is presented here for some of the formalisms devised for this purpose, covering the cosmological large-and small-scale structure, the astronomical static weak-field regime as well as emission and propagation effects for gravitational waves. This includes linear and nonlinear parametrized post-Friedmannian frameworks, effective field theory approaches, the parametrized post-Newtonian expansion, the parametrized post-Einsteinian formalism as well as an inspiral-merger-ringdown waveform model among others. Connections between the different formalisms are highlighted where they have been established and a brief outlook is provided for general steps towards a unified global framework for tests of gravity and dark sector models.

Inherently stable effective field theory for dark energy and modified gravity

“…The EFT description of the cosmological background and linear perturbations discussed here can furthermore be connected to a generalised phenomenological parametrisation of the screening mechanisms encountered in modified gravity theories [62] or post-Newtonian and post-Einsteinian expansions describing these modifications [56,63,64] (see Ref. [16] for a review).…”

“…3.2), Brans-Dicke scalar-tensor theories supplied with arbitrary potential and kinetic terms (Sec. 3.3), the minimal self-acceleration model [13,16] and no-slip gravity [66] (Sec. 3.4) as well as Horndeski theories with luminal speed of gravitational waves (Sec.…”

“…(3.15). For an even more specific example, we can then adopt the ΛCDM expansion history to be recovered such that 16) with H = H ΛCDM . In this case we do not have any free functions left.…”

“…In order to most effectively make use of this wealth of observations to infer the broadest of implications for the vast range of dark energy and modified gravity models conceivable, it has been of great interest to develop unified frameworks for making generalised predictions for this space of models (see, e.g., Ref. [16] for a review). Particularly successful has been the effective field theory (EFT) formalism for dark energy and modified gravity [17].…”

Tests of gravity with galaxy clusters

“…91,92). The reason being that clusters are non-linear objects, and screening mechanisms must be in action to guarantee that on small scales modifications of gravity are suppressed (see Koyama (2018), 2 Lombriser (2018), 88 Llinares (2018) 61 and Li (2018) 62 ). As a matter of fact, if screening conditions are satisfied there exists a screening scales R scr such that for radii R R scr gravity is back to GR, i.e.…”