Isotropic Observers and the Inflationary Backreaction Problem

Abstract

In an inflationary regime driven by a free massive inflaton we derive within a genuinely gauge invariant approach the backreaction effects due to long wavelength scalar fluctuations on the effective Hubble factor and equation of state with respect to a class of observers which sees an inhomogeneous and isotropic Universe. We find that, for such so-called isotropic observers, contrary to what happens for the observables defined by free-falling observers, there is an effect to leading order in the slow-roll parameter in the direction of slowing down the measured rate of expansion and of having an effective equation of state less de Sitter like. From a general point of view the isotropic observers result has to be considered complementary to other cases (observers) in helping to characterize the physical properties of the models under investigation.

16 pages, latex. Comments added, errors and typos corrected, main results unchanged. Version accepted for publication in Class. Quantum Grav

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• Invariant Measure of the One Loop Quantum Gravitational Back-Reaction on Inflation
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• Gauge invariant backreaction in general single field models of inflation
• Tensor Mode Backreaction During Slow-roll Inflation
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• Graviton backreaction on the local cosmological expansion in slow-roll inflation
• Synchronous coordinates and gauge-invariant observables in cosmological spacetimes
• Classical Gravitational Back-Reaction