Ewan R. M. Tarrant

Coupled quintessence and the halo mass function

A sufficiently light scalar field slowly evolving in a potential can account for the dark energy that presently dominates the Universe. This quintessence field is expected to couple directly to matter components, unless some symmetry of a more fundamental theory protects or suppresses it. Such a coupling would leave distinctive signatures in the background expansion history of the Universe and on cosmic structure formation, particularly at galaxy cluster scales. Using semianalytic expressions for the cold dark matter (CDM) halo mass function, we make predictions for halo abundance in models where the quintessence scalar field is coupled to cold dark matter, for a variety of quintessence potentials. We evaluate the linearly extrapolated density contrast at the redshift of collapse using the spherical collapse model and we compare this result to the corresponding prediction obtained from the nonlinear perturbation equations in the Newtonian limit. For all the models considered in this work, if there is a continuous flow of energy from the quintessence scalar field to the CDM component, then the predicted number of CDM haloes can only lie below that of

Perturbative reheating after multiple-field inflation: The impact on primordial observables

\ensuremath{\Lambda}\mathrm{CDM}

Scale-dependent non-Gaussianity and the CMB Power Asymmetry

, when each model shares the same cosmological parameters today. In the last stage of our analysis we perform a global MCMC fit to data to find the best fit values for the cosmological model parameters. We find that for some forms of the quintessence potential, coupled dark energy models can offer a viable alternative to

Influence of reheating on the trispectrum and its scale dependence

\ensuremath{\Lambda}\mathrm{CDM}

Cosmological effects of coupled dark matter

in light of the recent detections of massive high-

The dark energy cosmic clock: a new way to parametrise the equation of state

z

Cosmology of Axions and Moduli: A Dynamical Systems Approach

galaxy clusters, while other models of coupled quintessence predict a smaller number of massive clusters at high redshift compared to

Effect of reheating on predictions following multiple-field inflation

\ensuremath{\Lambda}\mathrm{CDM}

The hemispherical asymmetry from a scale-dependent inflationary bispectrum

.

Implications of the cosmic microwave background power asymmetry for the early universe

We study the impact of perturbative reheating on primordial observables in models of multiple{ eld ination. By performing a sudden decay calculation, we derive analytic expressions for the local{type non{linearity parameterf local NL , the scalar spectral indexn , and the tensor{to{scalar ratio rT as functions of the decay rates of the inationary elds. We compare our analytic results to a fully numerical classical eld theory simulation, nding excellent agreement. We nd that the sensitivity of fNL, n , and rT to the reheating phase depends heavily on the underlying inationary model. We quantify this sensitivity, and discuss conditions that must be satised if observable predictions are to be insensitive to the dynamics of reheating. We demonstrate that upon completion of reheating, all observable quantities take values within nite ranges, the limits of which are determined completely by the conditions during ination. Furthermore, uctuations in both elds play an important role in determining the full dependence of the observables on the dynamics of reheating. By applying our formalism to two concrete examples, we demonstrate that variations in fNL, n , and rT caused by changes in reheating dynamics are well within the sensitivity of Planck, and as such the impact of reheating must be accounted for when making predictions for models of multiple{eld ination. Our nal expressions are very general, encompassing a wide range of two{eld inationary models, including the standard curvaton scenario. We show that the curvaton scenario is a limiting case of two{eld ination, and recover the standard curvaton results in the appropriate limit. Our results allow a much more unied approach to studying two{eld ination including the eects of perturbative reheating. As such, entire classes of models can be studied together, allowing a more systematic approach to gaining insight into the physics of the early universe through observation.