We study the effects of perturbative reheating on the evolution of the curvature perturbation ζ, in two-field inflation models. We use numerical methods to explore the sensitivity of fNL, n ζ and r to the reheating process, and present simple qualitative arguments to explain our results. In general, if a large non-Gaussian signal exists at the start of reheating, it will remain non-zero at the end of reheating. Unless all isocurvature modes have completely decayed before the start of reheating, we find that the non-linearity parameter, fNL, can be sensitive to the reheating timescale, and that this dependence is most appreciable for 'runaway' inflationary potentials that only have a minimum in one direction. For potentials with a minimum in both directions, fNL can also be sensitive to reheating if a mild hierarchy exists between the decay rates of each field. Within the class of models studied, we find that the spectral index n ζ , is fairly insensitive to large changes in the field decay rates, indicating that n ζ is a more robust inflationary observable, unlike the non-linearity parameter fNL. Our results imply that the statistics of ζ, especially fNL, can only be reliably used to discriminate between models of two-field inflation if the physics of reheating are properly accounted for.

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 ÃCDM, 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 ÃCDM in light of the recent detections of massive high-z galaxy clusters, while other models of coupled quintessence predict a smaller number of massive clusters at high redshift compared to ÃCDM.

We study the impact of perturbative reheating on primordial observables in models of multiplefield inflation. By performing a sudden decay calculation, we derive analytic expressions for the local-type non-linearity parameter f local NL , the scalar spectral index n ζ , and the tensor-to-scalar ratio rT as functions of the decay rates of the inflationary fields. We compare our analytic results to a fully numerical classical field theory simulation, finding excellent agreement. We find that the sensitivity of fNL, n ζ , and rT to the reheating phase depends heavily on the underlying inflationary model. We quantify this sensitivity, and discuss conditions that must be satisfied 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 finite ranges, the limits of which are determined completely by the conditions during inflation. Furthermore, fluctuations in both fields 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 ζ , 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-field inflation. Our final expressions are very general, encompassing a wide range of two-field inflationary models, including the standard curvaton scenario. We show that the curvaton scenario is a limiting case of two-field inflation, and recover the standard curvaton results in the appropriate limit. Our results allow a much more unified approach to studying two-field inflation including the effects 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.

The flatness of the inflaton potential and lightness of the Higgs boson could have the common origin of the breaking of a global symmetry. This scenario provides a unified framework of Goldstone inflation and composite Higgs models, where the inflaton and the Higgs particle both have a pseudoGoldstone boson nature. The inflaton reheats the Universe via decays to the Higgs and subsequent secondzary production of other SM particles via the top and massive vector bosons. We find that inflationary predictions and perturbative reheating conditions are consistent with cosmic microwave background data for sub-Planckian values of the fields, as well as opening up the possibility of inflation at the TeV scale. We explore this exciting possibility, leading to an interplay between collider data cosmological constraints.