P. P. Avelino

Alternatives to Quintessence Model-building

We discuss the issue of toy model building for the dark energy component of the universe. Specifically, we consider two generic toy models recently proposed as alternatives to quintessence models, respectively known as Cardassian expansion and the Chaplygin gas. We show that the former is entirely equivalent to a class of quintessence models. We determine the observational constraints on the latter, coming from recent supernovae results and from the shape of the matter power spectrum. As expected, these restrict the model to a behaviour that closely matches that of a standard cosmological constant �.

Bouncing Eddington-inspired Born-Infeld cosmologies: An alternative to inflation?

We study the dynamics of a homogeneous and isotropic Friedmann-Robertson-Walker universe in the context of the Eddington-inspired Born-Infeld theory of gravity. We generalize earlier results, obtained in the context of a radiation dominated universe, to account for the evolution of a universe permeated by a perfect fluid with an arbitrary equation of state parameter

Reconstructing the dark energy equation of state with varying couplings

w

Looking for a varying alpha in the cosmic microwave background

. We show that a bounce may occur for

WMAP constraints on varying α and the promise of reionization

\kappa >0

Measuring α in the early Universe: cosmic microwave background polarization, re‐ionization and the Fisher matrix analysis

, if

Cosmological evolution of domain wall networks

w

Cosmic-String–Seeded Structure Formation

is time-dependent, and we demonstrate that it is free from tensor singularities. We argue that Eddington-inspired Born-Infeld cosmologies may be a viable alternative to the inflationary paradigm as a solution to fundamental problems of the standard cosmological model.

Frustrated expectations: defect networks and dark energy

We revisit the idea of using varying couplings to probe the nature of dark energy, in particular, by reconstructing its equation of state. We show that for the class of models studied this method can be far superior to the standard methods (using type Ia supernovae or weak lensing). We also show that the simultaneous use of measurements of the fine-structure constant {alpha} and the electron-to-proton mass ratio {mu} allows a direct probe of grand unification scenarios. We present forecasts for the sensitivity of this method, both for the near future and for the next generation of spectrographs--for the latter we focus on the planned CODEX instrument for ESOs Extremely Large Telescope (formerly known as OWL). A high-accuracy reconstruction of the equation of state may be possible all the way up to redshift z{approx}4.

Measuring alpha in the early universe. 1. CMB temperature, large scale structure and fisher matrix analysis

We perform a likelihood analysis of the recently released BOOMERanG and MAXIMA data, allowing for the possibility of a time-varying fine-structure constant. We find that in general this data prefers a value of