Imperfect Dark Energy from Kinetic Gravity Braiding

By Cedric Deffayet, O. Pujolàs, I. Sawicki, A. Vikman. 2010

673 citations recorded by the source corpus.

We introduce a large class of scalar-tensor models with interactions containing the second derivatives of the scalar field but not leading to additional degrees of freedom. These models exhibit peculiar features, such as an essential mixing of scalar and tensor kinetic terms, which we have named kinetic braiding. This braiding causes the scalar stress tensor to deviate from the perfect-fluid form. Cosmology in these models possesses a rich phenomenology, even in the limit where the scalar is an exact Goldstone boson. Generically, there are attractor solutions where the scalar monitors the behaviour of external matter. Because of the kinetic braiding, the position of the attractor depends both on the form of the Lagrangian and on the external energy density. The late-time asymptotic of these cosmologies is a de Sitter state. The scalar can exhibit phantom behaviour and is able to cross the phantom divide with neither ghosts nor gradient instabilities. These features provide a new class of models for Dark Energy. As an example, we study in detail a simple one-parameter model. The possible observational signatures of this model include a sizeable Early Dark Energy and a specific equation of state evolving into the final de-Sitter state from a healthy phantom regime.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/8235bfa5f7d305d164bb5a4f1cc6be72b9d0566e

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Citations in the corpus

hi_class: Horndeski in the Cosmic Linear Anisotropy Solving System (2016, background): “2 This general class of actions includes the vast majority of universally coupled models of dark energy with one scalar degree of freedom: quintessence [18, 19], Brans-Dicke models [20], k-essence [21, 22], kinetic gravity braiding [23–25], covariant galileons [15, 26], disformal and Dirac-Born-Infe”
The effective field theory of dark energy (2012, methodology): “3 Kinetic braiding It is straightforward to show that the operator G(φ,X) φ , (83) denoted in [49] as kinetic braiding, can also be rewritten as a polynomial of δg and δK with at most one power of δK.”
The imperfect fluid behind kinetic gravity braiding (2011, methodology): “The presence of third-order derivatives might have been expected owing to the d’Alembertian term in the action; however, as we have proven in [56], the equation of motion contains at most second-order derivatives.”
Effective field theory of cosmological perturbations (2013, background): “The specific type of modification of gravity that the operator m(3)3 is responsible for has been named “kinetic gravity braiding” [94], although it was previously studied in [6, 8, 29].”
Cosmology and Fundamental Physics with the Euclid Satellite (2012, background): “If the couplings are universal, the most general class of models where Q = 1 while there is no anisotropic stress are kinetic gravity braiding models of dark energy (Deffayet et al. 2010), which are a class of imperfect fluids (Pujolas et al.”
Asymptotically flat black holes in Horndeski theory and beyond (2017, background): “ sign in the standard kinetic term. The stability, however, also depends on the quartic Galileon term. Therefore, one cannot conclude on the stability of the solutions only by the sign of , see e.g. [34,35]. We will leave such an analysis for future work. The solution presented above is asymptotical”
Holographic dark energy (2016, background): “It should be noticed that nowadays, the phantom instability problem may be avoided, thanks to the Galileons [378, 379], and more generally the Horndeski theory [352].”
Effective field theory of dark energy: A review (2019, methodology): “[96, 97, 318, 319], the Kinetic Gravity Braiding model [93], the shift symmetric GLPV model [274], the tracking and scaling DHOST theories discussed in Ref.”
Does the Hubble constant tension call for new physics? (2018, background): “Derived from a canonical scalar field, the Hamiltonian has negative kinetic energy and is thus susceptible to vacuum instabilities [63], however see also [64].”
Exploring gravitational theories beyond Horndeski (2014, background): “In particular, M(2), αK , αB and αT respectively parameterize the effective Planck mass, a modification of the scalar kinetic term [34, 35], a kinetic mixing between the scalar and the metric (the so-called braiding) [36, 37, 38, 39] and a tensor speed excess.”
A unifying description of dark energy (2014, background): “This phenomenon has been called kinetic braiding in [36, 37].”