arXiv subjects

Ian J Grivell

Publications and source records attributed to Ian J Grivell.

5 recordsLinked to original sources

arXiv2000

Black hole constraints on the running-mass inflation model

The running-mass inflation model, which has strong motivation from particle physics, predicts density perturbations whose spectral index is strongly scale-dependent. For a large part of parameter space the spectrum rises sharply to short scales. In this paper we compute the production of primordial black holes, using both analytic and numerical calculation of the density perturbation spectra. Observational constraints from black hole production are shown to exclude a large region of otherwise permissible parameter space.

astro-ph↗

arXiv2000

Inflaton potential reconstruction without slow-roll

We describe a method of obtaining the inflationary potential from observations which does not use the slow-roll approximation. Rather, the microwave anisotropy spectrum is obtained directly from a parametrized potential numerically, with no approximation beyond linear perturbation theory. This permits unbiased estimation of the parameters describing the potential, as well as providing the full error covariance matrix. We illustrate the typical uncertainties obtained using the Fisher information matrix technique, studying the $λϕ^4$ potential in detail as a concrete example.

astro-ph↗

arXiv1998

Cosmological parameter estimation and the spectral index from inflation

Accurate estimation of cosmological parameters from microwave background anisotropies requires high-accuracy understanding of the cosmological model. Normally, a power-law spectrum of density perturbations is assumed, in which case the spectral index $n$ can be measured to around $\pm 0.004$ using microwave anisotropy satellites such as MAP and Planck. However, inflationary models generically predict that the spectral index $n$ of the density perturbation spectrum will be scale-dependent. We carry out a detailed investigation of the measurability of this scale dependence by Planck, including the influence of polarization on the parameter estimation. We also estimate the increase in the uncertainty in all other parameters if the scale dependence has to be included. This increase applies even if the scale dependence is too small to be measured unless it is assumed absent, but is shown to be a small effect. We study the implications for inflation models, beginning with a brief examination of the generic slow-roll inflation situation, and then move to a detailed examination of a recently-devised hybrid inflation model for which the scale dependence of $n$ may be observable.

astro-ph↗

arXiv1997

Accurately determining inflationary perturbations

Cosmic microwave anisotropy satellites promise extremely accurate measures of the amplitude of perturbations in the universe. We use a numerical code to test the accuracy of existing approximate expressions for the amplitude of perturbations produced by single-field inflation models. We find that the second-order Stewart-Lyth calculation gives extremely accurate results, typically better than one percent. We use our code to carry out an expansion about the general power-law inflation solution, providing a fitting function giving results of even higher accuracy.

astro-ph↗

arXiv1996

Accurate determination of inflationary perturbations

We use a numerical code for accurate computation of the amplitude of linear density perturbations and gravitational waves generated by single-field inflation models to study the accuracy of existing analytic results based on the slow-roll approximation. We use our code to calculate the coefficient of an expansion about the exact analytic result for power-law inflation; this generates a fitting function which can be applied to all inflationary models to obtain extremely accurate results. In the appropriate limit our results confirm the Stewart--Lyth analytic second-order calculation, and we find that their results are very accurate for inflationary models favoured by current observational constraints.

astro-ph↗