Interacting dark sector from the trace-free Einstein equations: Cosmological perturbations with no instability

Interacting Dark Energy and Cosmological Equations of State

Interactions within the cosmic medium modify its equation of state. We discuss implications of interacting dark energy models both for the spatially homogenous background and for the perturbation dynamics.

Interacting model for the cosmological dark

Cosmological Perturbations from the No Boundary Euclidean Path Integral

We compute, from first principles, the quantum fluctuations about instanton saddle points of the Euclidean path integral for Einstein gravity coupled to a scalar field. The Euclidean two-point correlator is analytically continued into the Lorentzian region where it describes the quantum mechanical vacuum fluctuations in the state described by no boundary proposal initial conditions. We concentr...

Cosmological Perturbations in Phantom Dark Energy Models

The ΛCDM paradigm, characterised by a constant equation of state w = −1 for dark energy, is the model that better fits observations. However, the same observations strongly support the possibility of a dark energy content where the corresponding equation of state is close to but slightly smaller than −1. In this regard, we focus on three different models where the dark energy content is describ...

Self–Interacting Dark Matter from the Hidden Heterotic–String Sector

It has been suggested recently that self–interacting dark matter fits better the observational characteristics of galaxy dynamics. We propose that the self–interacting dark matter is composed from the glueballs of the hidden sector non–Abelian gauge group, while the hidden matter states exist in vector–like representation and decouple from the light spectrum. It is shown that these glueballs ar...