Causality implies inflationary back-reaction

Abstract

There is a widespread belief among inflationary cosmologists that a local observer cannot sense super-horizon gravitons. The argument goes that a local observer would subsume super-horizon gravitons into a redefinition of his coordinate system. We show that adopting this view for pure gravity on de Sitter background leads to time variation in the Hubble parameter measured by a local observer. It also leads to a violation of the gravitational field equation R = 4Λ because that equation is obeyed by the full metric, rather than the one which has been cleansed of super-horizon modes.

One loop graviton corrections to dynamical photons in de Sitter

“…Worries have long been expressed that the large logarithms from loops of inflationary gravitons might be artifacts of the gauge or poorly chosen observables [15][16][17][18][19][20]. There are problems with invoking these arguments to deny the possibility of large logarithmic corrections [21][22][23][24], but they do highlight the importance of correctly computing the numerical coefficients. This has also been seen directly.…”

The Case for Nonlocal Modifications of Gravity

“…I'm a big believer in checking things when I can figure out how to do it. When I finally figured out how to check this belief, the result is that is that subsuming infrared gravitons into the background can neither eliminate secular growth [74] nor changes in the local expansion rate [75].…”