10.1088/1475-7516/2010/08/006
Byrnes, Christian
Christian
Byrnes
Gerstenlauer, M.
M.
Gerstenlauer
Hebecker, A.
A.
Hebecker
Nurmi, S.
S.
Nurmi
Tasinato, G.
G.
Tasinato
Inflationary infrared divergences: geometry of the reheating surface vs. delta N formalism
IOP Publishing
2010
2010-12-07T10:47:04Z
2018-07-24T12:57:49Z
journal_article
https://pub.uni-bielefeld.de/record/1929190
https://pub.uni-bielefeld.de/record/1929190.json
We describe a simple way of incorporating fluctuations of the Hubble scale during the horizon exit of scalar perturbations into the delta N formalism. The dominant effect comes from the dependence of the Hubble scale on low-frequency modes of the inflaton. This modifies the coefficient of the log-enhanced term appearing in the curvature spectrum at second order in field fluctuations. With this modification, the relevant coefficient turns out to be proportional to the second derivative of the tree-level spectrum with respect to the inflaton. at horizon exit. A logarithm with precisely the same coefficient appears in a calculation of the log-enhancement of the curvature spectrum based purely on the geometry of the reheating surface. We take this agreement as strong support for the proposed implementation of the dN formalism. Moreover, our analysis makes it apparent that the log-enhancement of the inflationary power-spectrum is indeed physical if this quantity is defined using a global coordinate system on the reheating surface (or any other post-inflationary surface of constant energy density). However, it can be avoided by defining the spectrum using invariant distances on this surface.