Cosmic Variance of the Spectral Index from Mode Coupling

Abstract

We demonstrate that local, scale-dependent non-Gaussianity can generate cosmic variance uncertainty in the observed spectral index of primordial curvature perturbations. In a universe much larger than our current Hubble volume, locally unobservable long wavelength modes can induce a scale-dependence in the power spectrum of typical subvolumes, so that the observed spectral index varies at a cosmologically significant level (|Δns | ~ O(0.04)). Similarly, we show that the observed bispectrum can have an induced scale dependence that varies about the global shape. If tensor modes are coupled to long wavelength modes of a second field, the locally observed tensor power and spectral index can also vary. All of these effects, which can be introduced in models where the observed non-Gaussianity is consistent with bounds from the Planck satellite, loosen the constraints that observations place on the parameters of theories of inflation with mode coupling. We suggest observational constraints that future measurements could aim for to close this window of cosmic variance uncertainty.

32 pages, 7 figures. JCAP published version. Conclusions expanded with numeric examples of cosmic variance

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Cited by in corpus (15)

• The Quest for B Modes from Inflationary Gravitational Waves
• Just enough inflation: power spectrum modifications at large scales
• Constraining the initial conditions of the Universe using large scale structure
• Large-scale anomalies in the cosmic microwave background as signatures of non-Gaussianity
• Fossilized Gravitational Wave Relic and Primordial Clocks
• Constraints on Gauge Field Production during Inflation
• Cosmic variance in inflation with two light scalars
• Curvature Perturbations From Stochastic Particle Production During Inflation
• Super cosmic variance from mode-coupling: A worked example
• Non-local bispectra from super cosmic variance
• Constraining primordial and gravitational mode coupling with the position-dependent bispectrum of the large-scale structure
• Statistical anisotropies in temperature and polarization fluctuations from a scale-dependent trispectrum
• Influence of Unobservable Modes on Correlation Functions during Inflation
• 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