H0 tension, phantom dark energy, and cosmological parameter degeneracies

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...

A Phantom Menace? Cosmological Consequences of a Dark Energy Component with Super-Negative Equation of State

It is extraordinary that a number of observations indicate that we live in a spatially flat, low matter density Universe, which is currently undergoing a period of accelerating expansion. The effort to explain this current state has focused attention on cosmological models in which the dominant component of the cosmic energy density has negative pressure, with an equation of state w ≥ −1. Remar...

The Cosmological Constant and Dark Energy

Physics invites the idea that space contains energy whose gravitational effect approximates that of Einstein’s cosmological constant, Λ; nowadays the concept is termed dark energy or quintessence. Physics also suggests the dark energy could be dynamical, allowing the arguably appealing picture that the dark energy density is evolving to its natural value, zero, and is small now because the expa...

Cosmological Constant and Dark Energy: Historical Insights

Dark Energy and Dark Matter from Cosmological Observations

The introduction of new observational techniques has in the past few years moved cosmology into the era of precision science. With the advent of precision measurements of the cosmic microwave background (CMB), large scale structure (LSS) of galaxies, and distant type Ia supernovae, a new paradigm of cosmology has been established. In this new standard model, the geometry is flat so that Ωtotal ...