5 papers
A constant equation of state for quintessence ?
Elisa Di Pietro, Jacques Demaret
Quintessence is often invoked to explain the universe acceleration suggested by the type Ia supernovae observations. The aim of this letter is to study the validity of using a cons…
Scale-factor duality in string Bianchi cosmologies
Elisa Di Pietro, Jacques Demaret
We apply the scale factor duality transformations introduced in the context of the effective string theory to the anisotropic Bianchi-type models. We find dual models for all the B…
O(d,d)-invariance in inhomogeneous string cosmologies with perfect fluid
Jacques Demaret, Elisa Di Pietro
In the first part of the present paper, we show that O(d,d)-invariance usually known in a homogeneous cosmological background written in terms of proper time can be extended to bac…
Local and Global Properties of the World
Jacques Demaret, Michael Heller, Dominique Lambert
The essence of the method of physics is inseparably connected with the problem of interplay between local and global properties of the universe. In the present paper we discuss thi…
Hamiltonian Formulation of Bianchi Cosmological Models in Quadratic Theories of Gravity
Jacques Demaret, Laurent Querella
We use Boulware's Hamiltonian formalism of quadratic gravity theories in order to analyze the classical behaviour of Bianchi cosmological models for a Lagrangian density containing…