MG11 
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Abstract

Smooth dynamical crossing of the phantom divide line in simple cosmological models

Simple scalar field cosmological models are considered describing gravity assisted crossing of the phantom divide line. This crossing or (de)-phantomization characterized by the change of the sign of the kinetic term of the scalar field is smooth and driven dynamically by the Einstein equations. Different cosmological scenarios, including the phantom phase of matter are sketched.

Cosmological netscape and Euclidean quantum gravity

We revisit the old idea of Euclidean quantum gravity alternative to the construction of the pure Hartle-Hawking quantum state. Creation from nothing is described by the density matrix given by the Euclidean path integral. Its calculation with back reaction of quantum matter properly taken into account suggests a novel picture of the early quantum Universe. Landscape of universes in the bounded range of the cosmological constant is created with mixed quasi-equilibrium state of high-temperature gas of particles of conformally invariant fields. Instantons with $\Lambda<\Lambda_{\rm min}$ are completely eliminated by infinite positive value of their action, which suggests solution to the problem of boundedness of the on-shell gravitational action in the infrared domain of Euclidean quantum gravity. The mechanism of this elimination is based on nonlocal contribution of quantum conformal anomaly mediated by a special ghost-avoiding ultraviolet renormalization. Upper bound of the cosmological landscape is saturated with the infinite sequence of increasingly long garland-type instantons.

Chaplygin-gas-like models of dark energy: the current status