Cosmological perturbations in generalised gravity theories: formulation

Abstract

The author presents a simple way of deriving cosmological perturbation equations in generalised gravity theories which accounts for metric perturbations in a gauge-invariant way. The author uses an imperfect fluid formulation of the perturbation equations developed in Einstein gravity and absorb all new contributions as effective fluid quantities. The author applies this approach to the f( phi , R)- omega ( phi ) phi ,c phi c Lagrangian which includes most of the gravity theories employing a scalar field and scalar curvature. The relation between the proposed method and the conformal transformation method is discussed. Background and perturbation equations are displayed for specific gravity theories which can be recovered as special cases from the above general Lagrangian.

de Sitter attractors in generalized gravity

“…We do not consider vector modes described by the quantity B since, as proven in Ref. [35], vorticity modes cannot be generated in generalized gravity when matter contributions are absent (i.e., when the scalar field or nonlinear corrections to R dominate). The vector mode B effectively disappears from the gauge-invariant variables ∆φ and Φ A = Φ H = −∆F/(2F 0 ) defined by mixing scalar modes and B.…”

“…Again, we consider scalar and tensor modes and drop the vector modes which cannot be generated in the absence of matter [35]. Inspection of eq.…”

Untitled

“…The formulation of Ref. [80] has been adapted to the case of a FLRW universe with flat spatial sections; the constant κ = 8πG has been restored. Only first order calculations in the perturbations are presented here.…”

“…When ǫ H and η H increase, the kinetic energy of the inflaton increases and, when ǫ H and η H become of order unity, the slow-roll approximation breaks down and inflation ends. Slow-roll parameters have been identified also for generalized inflation [80,81,82,83]; the novelty is that there are four such parameters as opposed to the two of ordinary inflation. From the point of view of Sec.…”

Inflação em modelos de gravidade generalizada: análise dinâmica e singularidades

“…Esta escolhaé motivada pelo fato que quando admite-se uma cosmologia homogênea e isotrópica, considera-se que todos os invariantes do tensor de Ricci podem ser escritos em termos de R. A ação (6.3) inclui todos os casos especiais tais como teoria de Brans-Dicke, teorias escalares-tensoriais, gravidade modificada, lagrangianas quadráticas, a teoria de um campo não-minimamente acoplado ao escalar de Ricci, relatividade geral sem ou com um campo minimamente acoplado e uma constante cosmológica e teoria de campos de phantom. A variação desta ação conduzàs equações de campo de gravidade generalizada [31],…”