arXiv subjects

John Ronayne

Publications and source records attributed to John Ronayne.

4 recordsLinked to original sources

arXiv2020

Non-Gaussianity after many-field reheating

We numerically investigate reheating after quadratic inflation with up to 65 fields, focusing on the production of non-Gaussianity. We consider several sets of initial conditions, masses and decay rates. As expected we find that the reheating phase can have a significant effect on the non-Gaussian signal, but that for this number of fields a detectable level of non-Gaussianity requires the initial conditions, mass range and decay rates to be ordered in a particular way. We speculate on whether this might change in the N-flation limit.

astro-ph.CO↗

arXiv2019

Hyper non-Gaussianities in inflation with strongly non-geodesic motion

Several recent proposals to embed inflation into high-energy physics rely on inflationary dynamics characterized by a strongly non-geodesic motion in negatively curved field space. This naturally leads to a transient instability of perturbations on sub-Hubble scales, and to their exponential amplification. Supported by first-principle numerical computations, and by the analytical insight provided by the effective field theory of inflation, we show that the bispectrum is enhanced in flattened configurations, and we argue that an analogous result holds for all higher-order correlation functions. These ``hyper non-Gaussianities'' thus provide powerful model-independent constraints on non-standard inflationary attractors motivated by the search for ultraviolet completions of inflation.

hep-th↗

arXiv2018

Primordial fluctuations and non-Gaussianities in sidetracked inflation

Heavy scalar fields can undergo an instability during inflation as a result of their kinetic couplings with the inflaton. This is known as the geometrical destabilization of inflation, as it relies on the effect of the negative curvature of the field-space manifold overcoming the stabilizing force of the potential. This instability can drive the system away from its original path in field space into a new inflationary attractor, a scenario that we dub sidetracked inflation. We study this second phase and its observable consequences in several classes of two-field models. We show that cosmological fluctuations exhibit varied behaviours depending on the potential and the field space geometry, and that they can be captured by single-field effective theories with either a modified dispersion relation, a reduced speed of sound, or an imaginary one --- the latter case describing a transient tachyonic growth of the fluctuations. We also numerically calculate the bispectrum with the transport approach, finding large non-Gaussianities of equilateral and orthogonal shapes. In the hyperbolic geometry the potentials of our models present a pole at the boundary of the Poincaré disk and we discuss their relationships with $α$-attractors.

astro-ph.CO↗

arXiv2018

Attractor Behaviour in Multifield Inflation

We study multifield inflation in scenarios where the fields are coupled non-minimally to gravity via $ξ_I(ϕ^I)^n g^{μν}R_{μν}$, where $ξ_I$ are coupling constants, $ϕ^I$ the fields driving inflation, $g_{μν}$ the space-time metric, $R_{μν}$ the Ricci tensor, and $n>0$. We consider the so-called $α$-attractor models in two formulations of gravity: in the usual metric case where $R_{μν}=R_{μν}(g_{μν})$, and in the Palatini formulation where $R_{μν}$ is an independent variable. As the main result, we show that, regardless of the underlying theory of gravity, the field-space curvature in the Einstein frame has no influence on the inflationary dynamics at the limit of large $ξ_I$, and one effectively retains the single-field case. However, the gravity formulation does play an important role: in the metric case the result means that multifield models approach the single-field $α$-attractor limit, whereas in the Palatini case the attractor behaviour is lost also in the case of multifield inflation. We discuss what this means for distinguishing between different models of inflation.

astro-ph.CO↗