Kinetically coupled dark energy

Abstract

The main goal of this work is to propose a generalized model of interacting dark energy which allows for the kinetic term of a scalar field to couple to the matter species a priori in the action. We derive the modified field equations, and present novel cosmological solutions for a specific coupled model. One alluring consequence is the emergence of solutions allowing for an early scaling regime, possible due to two novel critical points, followed by a period of accelerated expansion. Using a dynamical system analysis, we show that the presence of the coupling may alter the dynamical nature of the critical points and can be used to enlarge the existence and stability regions of these. Using constraints from Planck data we are able to find an upper bound on the coupling parameter. Finally, it is shown how this theory encapsulates a wide variety of dark energy models already present in the literature.

Disformally coupled quintessence

“…In the plainest scenarios, DE is portrayed as a canonical scalar field, the quintessence field, which does not interact with the other components in the Universe [13,14]. However, there is no fundamental reason to assume such a constraint and, in the simplest extension, the scalar field is allowed to couple non-minimally to the matter sector [15][16][17][18][19][20][21][22][23].One straightforward procedure for introducing a non-trivial coupling between the scalar field and matter is to consider that matter particles propagate in geodesics of a transformed metric,ḡ µν , related to the gravitational metric, g µν , by means of a field-dependent transformation. When this transformation corresponds to a rescaling of the metric we speak of conformal transformations, which affect the length of time-like and space-like intervals and the norm of time-like and space-like vectors while leaving the light cones unchanged:where C is the conformal factor.…”

Scalar-field dark energy nonminimally and kinetically coupled to dark matter

“…We considered the new interacting action (2.4) containing the X dependence in the couplings f 1 and f 2 . Our analysis is sufficiently general in that it accommodates a wide variety of nonminimal and derivative couplings studied in the literature [23,25,48,49,55,68]. Moreover, unlike most of past related papers, we did not restrict the dark energy field to quintessence or k-essence.…”

“…The background cosmological dynamics with the first interaction was recently discussed for a canonical field with the potential V (φ) [68]. The interacting Lagrangians L int1 and L int2 are also related to the theories in which CDM is conformally and disformally coupled to the metricḡ µν different from the metric g µν felt by baryons [69][70][71].…”

Weak cosmic growth in coupled dark energy with a Lagrangian formulation

“…If a scalar field φ is responsible for the DE sector, the first possible interacting Lagrangian is of the form L int1 = − √ −gf 1 (φ, X)ρ c (n c ) [34,40,50], where g is the determinant of metric tensor g µν , f 1 is a function of φ and X = −∂ µ φ∂ µ φ/2, and ρ c depends on the CDM number density n c . The φ-dependent coupling f 1 arises from nonminimally coupled gravitational theories after the conformal transformation to the Einstein frame [51,52].…”

“…[55,56]). Inclusion of X dependence in f 1 leads to different dynamics of background and perturbations [40,50].…”