Adiabatic and isocurvature perturbation projections in multi-field inflation

Gordon, Chris; Saffin, Paul M.

Abstract

Current data are in good agreement with the predictions of single field inflation. However, the hemispherical asymmetry seen in the cosmic microwave background data, may hint at a potential problem. Generalizing to multi-field models may provide one possible explanation. A useful way of modeling perturbations in multi-field inflation is to investigate the projection of the perturbation along and perpendicular to the background fields' trajectory. These correspond to the adiabatic and isocurvature perturbations. However, it is important to note that in general there are no corresponding adiabatic and isocurvature fields. The purpose of this article is to highlight the distinction between a field redefinition and a perturbation projection. We provide a detailed derivation of the evolution of the isocurvature perturbation to show that no assumption of an adiabatic or isocurvature field is needed. We also show how this evolution equation is consistent with the field covariant evolution equations for the isocurvature perturbation in the flat field space limit.

• Journal Article Type: Article
• Publication Date: Aug 12, 2013
• Journal: Journal of Cosmology and Astroparticle Physics
• Electronic ISSN: 1475-7516
• Publisher: IOP Publishing
• Peer Reviewed: Peer Reviewed
• Volume: 2013
• Issue: 8
• Article Number: 021
• APA6 Citation: Gordon, C., & Saffin, P. M. (2013). Adiabatic and isocurvature perturbation projections in multi-field inflation. Journal of Cosmology and Astroparticle Physics, 2013(8), https://doi.org/10.1088/1475-7516/2013/08/021
• DOI: https://doi.org/10.1088/1475-7516/2013/08/021
• Keywords: Inflation, Cosmological perturbation theory
• Publisher URL: https://doi.org/10.1088/1475-7516/2013/08/021
• Copyright Statement: Copyright information regarding this work can be found at the following address: http://eprints.nottingh.../end_user_agreement.pdf
• Additional Information: This is an author-created, un-copyedited version of an article accepted for publication/published; in Journal of Cosmology and Astroparticle Physics. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at https://doi.org/10.1088/1475-7516/2013/08/021