Inhomogeneous vacuum energy

Abstract

Vacuum energy remains the simplest model of dark energy which could drive the accelerated expansion of the Universe without necessarily introducing any new degrees of freedom. Inhomogeneous vacuum energy is necessarily interacting in general relativity. Although the four-velocity of vacuum energy is undefined, an interacting vacuum has an energy transfer and the vacuum energy defines a particular foliation of spacetime with spatially homogeneous vacuum energy in cosmological solutions. It is possible to give a consistent description of vacuum dynamics and in particular the relativistic equations of motion for inhomogeneous perturbations given a covariant prescription for the vacuum energy, or equivalently the energy transfer four-vector, and we construct gauge-invariant vacuum perturbations. We show that any dark energy cosmology can be decomposed into an interacting vacuum+matter cosmology whose inhomogeneous perturbations obey simple first-order equations.

New constraints on interacting dark energy from cosmic chronometers

“…Clearly, in the absence of a coupling with the CDM component, the conventional dynamical dark energy scenario is recovered. Note that for w = −1 and δ = 0, we may identify ρ de = ρ vacuum and the above expressions reduce to the vacuum decaying scenario [28][29][30][31][32][33][34].…”

“…We follow [55,56], where a synchronous gauge has been adopted, and thus the line element of the linearly perturbed FRW metric can be written as…”

Braneworld gravity within non-conservative gravitational theory

“…(12) that this model of gravity provides a braneworld scenario with a running effective cosmological "constant". As such this novel aspect is promising for cosmology as it can make feasible the emerging of interactions between dark energy and dark matter [17][18][19][20][21][22][23][24][25][26].…”

“…This equation carries an effective cosmological constant which now becomes a function of the coordinates due to the terms inherited from the modified gravity. This feature is attractive from the cosmological point of view, as a time-dependent cosmological "constant" makes possible a construction of a model of universe where the components of the dark sector are able to interact each other, exchanging energy and momentum [17][18][19][20][21][22][23][24][25][26]. This class of cosmologies usually comes into play as an attempt of addressing the socalled "coincidence problem" [27].…”

“…For instance, by working with a particular case in which λ A = (0, λ r ), then from Eqs. (25) and (26) …”