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Friedmann-Robertson-Walker universes with a presently large fraction of the energy density stored in an X-component with w X < −1/3, are considered. We find all the critical points of the system for constant equations of state in that range. We consider further several background quantities that can distinguish the models with different w X values. Using a… (More)

Transition to the semiclassical behaviour and the decoherence process for inhomogeneous perturbations generated from the vacuum state during an inflationary stage in the early Universe are considered both in the Heisenberg and the Schrödinger representations to show explicitly that both approaches lead to the same prediction: the equivalence of these… (More)

We consider scalar-tensor theories of gravity in an accelerating universe. The equations for the background evolution and the perturbations are given in full generality for any parametrization of the Lagrangian, and we stress that apparent singularities are sometimes artifacts of a pathological choice of variables. Adopting a phenomenological viewpoint,… (More)

- Radouane Gannouji, David Polarski, André Ranquet, Alexei A. Starobinsky
- 2008

We consider the viability of dark energy (DE) models in the framework of the scalar-tensor theory of gravity, including the possibility to have a phantom DE at small redshifts z as admitted by supernova luminosity-distance data. For small z, the generic solution for these models is constructed in the form of a power series in z without any approximation.… (More)

Dynamics of long-wave isocurvature perturbations during an inflationary stage in multiple (multi-component) inflationary models is calculated analytically for the case where scalar fields producing this stage interact between themselves through gravity only. This enables to determine correct amplitudes of such perturbations produced by vacuum quantum… (More)

- Luca Amendola, David Polarski, Shinji Tsujikawa
- Physical review letters
- 2007

All f(R) modified gravity theories are conformally identical to models of quintessence in which matter is coupled to dark energy with a strong coupling. This coupling induces a cosmological evolution radically different from standard cosmology. We find that, in all f(R) theories where a power of R is dominant at large or small R (which include most of those… (More)

We consider the observational constraints from the detection of antiprotons in the Galaxy on the amount of Primordial Black Holes (PBH) produced from primordial power spectra with a bumpy mass variance. Though essentially equivalent at the present time to the constraints from the diffuse γ-ray background, they allow a widely independent approach and they… (More)

- David Polarski, André Ranquet
- 2006

The formalism in order to obtain the Dark Energy equation of state is extended to non-flat universes and we consider the inequalities that must be satisfied by Phantom Dark Energy in this case. We show that due to a non-vanishing spatial curvature satisfying the observational bounds, the uncertainty on the determination of the Dark Energy equation of state… (More)

Transition from quantum to semiclassical behaviour and loss of quantum coherence for inhomogeneous perturbations generated from a non-vacuum initial state in the early Universe is considered in the Heisenberg and the Schrödinger representations, as well as using the Wigner function. We show explicitly that these three approaches lead to the same prediction… (More)

We consider double-inflationary models with two noninteracting scalar fields, a light scalar field φ l with potential 1 2 m 2 l φ 2 l and a heavy scalar field φ h with potential λ n φ n h with n = 2, 4. CDM with the initial spectrum of adiabatic perturbations produced in these models is compared with observations. These models contain two more free… (More)