Super cosmic variance from mode-coupling: A worked example

Abstract

If the entire post-inflationary patch is large compared to our Hubble volume even a small level of non-Gaussianity can cause statistics of the primordial curvature field in our Hubble volume to be biased by mode-coupling. We explicitly compute the variation of locally measured statistics of the primordial curvature $\zeta$ from non-Gaussian mode coupling within a specific inflationary scenario: the curvaton model with a quadratic curvaton potential. This "super cosmic variance" is calculated in two ways: (i) as a super observer who has access to the curvature perturbation field across the entire post-inflationary patch and therefore sees local statistics as biased by mode coupling and (ii) as a local observer who sees the statistics of $\zeta$ determined by the local values of quantities in their Hubble patch. The two calculations agree and show that in the quadratic curvaton model patch-to-patch differences in statistics of $\zeta$ can be interpreted entirely as a shift in the value of the curvaton field at freeze out. Applying the same arguments to single-field slow-roll inflation gives a simple picture of how non-Gaussian mode-coupling between the curvature perturbations on very different physical scales must vanish in the attractor limit.

9 pages, no figures; v2 typos corrected, references added, matches PRD accepted version

References in corpus (6)

• CMBPol Mission Concept Study: Probing Inflation with CMB Polarization
• The Observed Squeezed Limit of Cosmological Three-Point Functions
• In-in and $\delta N$ calculations of the bispectrum from non-attractor single-field inflation
• Generalized Slow Roll for Non-Canonical Kinetic Terms
• Cosmic Variance of the Spectral Index from Mode Coupling
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Cited by in corpus (11)

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• Large-scale anomalies in the cosmic microwave background as signatures of non-Gaussianity
• Constraints on Gauge Field Production during Inflation
• The observed galaxy bispectrum from single-field inflation in the squeezed limit
• Cosmic variance in inflation with two light scalars
• Statistics of Anisotropies in Inflation with Spectator Vector Fields
• Local Observables in a Landscape of Infrared Gauge Modes
• Non-local bispectra from super cosmic variance
• On the space of non-Gaussian fields with single-clock bispectra
• Beyond the Hubble scale: Super cosmic variance and nongaussianity as a portal to the superhorizon