Maximal freedom at minimum cost: linear large-scale structure in general modifications of gravity

By Emilio Bellini, I. Sawicki. 2014

389 citations recorded by the source corpus.

We present a turnkey solution, ready for implementation in numerical codes, for the study of linear structure formation in general scalar-tensor models involving a single universally coupled scalar field. We show that the totality of cosmological information on the gravitational sector can be compressed — without any redundancy — into five independent and arbitrary functions of time only and one constant. These describe physical properties of the universe: the observable background expansion history, fractional matter density today, and four functions of time describing the properties of the dark energy. We show that two of those dark-energy property functions control the existence of anisotropic stress, the other two — dark-energy clustering, both of which are can be scale-dependent. All these properties can in principle be measured, but no information on the underlying theory of acceleration beyond this can be obtained. We present a translation between popular models of late-time acceleration (e.g. perfect fluids, f(R), kinetic gravity braiding, galileons), as well as the effective field theory framework, and our formulation. In this way, implementing this formulation numerically would give a single tool which could consistently test the majority of models of late-time acceleration heretofore proposed.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/5a9ca9f731906882d014d62716ebf1894e18568f

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Citations in the corpus

Cosmology and Fundamental Physics with the Euclid Satellite (2012, methodology): “It is present in archetypal modified gravity models such as f (R) gravity (see (Bellini and Sawicki 2014) for details).”
Dark Energy in Light of Multi-Messenger Gravitational-Wave Astronomy (2018, background): “Some non-trivial special cases are known to exist: f (R) and f (G) theories have αK = 0, while first generation theories (3) including f (R), Brans-Dicke satisfy αB + αM = 0 (Bellini and Sawicki, 2014) and 2 beyond Horndeski combinations produce αT = 0 (Creminelli and Vernizzi, 2017; Ezquiaga and Zu”
Beyond the Cosmological Standard Model (2014, positive): “This takes us from two functions of time and scale to five functions of time, which are significantly easier to constrain from observations (see also [941, 980, 981]).”
hi_class: Horndeski in the Cosmic Linear Anisotropy Solving System (2016, background): “It is present in archetypal modified gravity models such as Brans-Dicke and f(R) gravity (see [54] for details).”
Effective description of higher-order scalar-tensor theories (2017, background): “The above quadratic action extends the one derived in [4] and written in terms of the dimensionless time-dependent functions αA (introduced in [16] and [17]) in [7], with the addition of four new functions of time: the parameter αL, and the three parameters βA that characterize the terms containing ”
Scalar-tensor theories and modified gravity in the wake of GW170817 (2017, background): “It is also worth noting that the coefficients Ξi can be related to two of the cosmological effective parameters, namely αH and β1, introduced in the effective description of dark energy in [28] and [9], extending the parameters of [29] to Beyond Horndeski and DHOST theories.”
Exploring gravitational theories beyond Horndeski (2014, background): “[14], where they consider linear perturbations in Horndeski theories, with the difference α B = −α there B /2, which simplifies further the equations.”
Galileon gravity in light of ISW, CMB, BAO and H0 data (2017, background): “The existence of the tracker is a direct consequence of shift symmetry (φ → φ + c), by virtue of which the evolution of the field is equivalent to the covariant conservation of the shift-current [63] ∇μJ μ ⇒ J̇ 0 + 3HJ 0 = 0, where J 0 is defined in Eq.”
Dark energy and modified gravity in degenerate higher-order scalar–tensor (DHOST) theories: A review (2018, background): “Most of these papers use either the phenomenological parameters μ ≡ Gmatter/G and Σ ≡ Glight/G, or the functions αI(t) introduced in [44].”
A unifying description of dark energy (2014, methodology): “However, as discussed in [26] this does not give the same result as neglecting time derivatives in eq.”
Gravitational wave decay into dark energy (2018, background): “The first quantity, α, sets the normalization of the scalar fluctuations and must be positive while αB [34] and αH [24] measure the kinetic mixing of the scalar respectively with gravity and matter.”