Exploring Two-Field Inflation in the Wess-Zumino Model

We explore inflation via the effective potential of the minimal Wess-Zumino model, considering both the real and imaginary components of the complex field. Using transport techniques, we calculate the full allowed range of $n_s$, $r$ and $f_{\rm NL}$ for different choices of the single free parameter, $v$, and present the probability distribution of these signatures given a simple choice for the prior distribution of initial conditions. Our work provides a case study of multi-field inflation in a simple but realistic setting, with important lessons that are likely to apply more generally. For example, we find that there are initial conditions consistent with observations of $n_s$ and $r$ for values of $v$ that would be excluded if only evolutions in the real field direction were to be considered, and that these may yield enhanced values of $f_{\rm NL}$. Moreover, we find that initial conditions fixed at high energy density, where the potential is close to quartic in form, can still lead to evolutions in a concave region of the potential during the observable number of e-folds, as preferred by present data. The Wess-Zumino model therefore provides an illustration that multi-field dynamics must be taken into account when seeking to understand fully the phenomenology of such models of inflation.Comment: 19 pages, 6 figure

Three-form inflation and non-Gaussianity

We calculate the perturbed action, at second and third order, for a massive three-form field minimally coupled to gravity, and use it to explore the observational predictions of three-form inflation. One intriguing result is that the value of the spectral index is nearly independent of the three-form potential, being fixed solely by the number of e-folds of inflation, with n_s=0.97 for the canonical number of 60. Considering the bispectrum, we employ standard techniques to give explicit results for two models, one of which produces a large non-Gaussianity. Finally, we confirm our results by employing a duality relating the three-form theory to a non-canonical scalar field theory and explicitly re-computing results in this dual picture.Comment: 23 pages, 6 figures. Typos corrected and addition of one appendix. Accepted in JCA

The dynamics of cosmological scenarios inspired by quantum gravity

PhDIn this thesis we study the dynamics of cosmological scenarios inspired by quantum gravity. Part I investigates novel features of the semi-classical regime of homogeneous and isotropic loop quantum cosmology. Dynamics in this regime becomes modified by nonperturbative quantum effects, subject to a number of ambiguities. For a flat universe the quantum effects accelerate a scalar field along its self-interaction potential during a period of super-inflation. We study how this behaviour can in principle set the initial conditions for subsequent slow-roll inflation. We also calculate a first approximation for the spectrum of perturbations produced during the super-inflationary phase. For the positively-curved case we investigate how a bounce from a contracting to an expanding phase can occur, and show that this can lead to oscillations of the universe. During the oscillations the inflaton field can roll monotonically up its potential. Once the potential energy becomes sufficiently large, however, the cycles end and inflation commences. For a constant potential the oscillations occur about a centre fixed point allowing the construction of `new emergent universe' scenarios where the universe is past-eternally an Einstein static universe, but subsequently evolves into inflation. Part II considers positively-curved braneworld models in which the dynamical equations become modified in such a way as to permit a bounce. It is conjectured that models of this type can exhibit similar behaviour to the positively-curved LQC scenario. General conditions for this behaviour are determined in braneworld settings and we investigate an explicit example - the baneworld of Shtanov and Sanhi - in detai