TY - JOUR
T1 - Cosmic variance of the spectral index from mode coupling
AU - Bramante, Joseph
AU - Kumar, Jason
AU - Nelson, Elliot
AU - Shandera, Sarah
PY - 2013/11
Y1 - 2013/11
N2 - 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| ∼ (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.
AB - 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| ∼ (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.
UR - http://www.scopus.com/inward/record.url?scp=84888614498&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=84888614498&partnerID=8YFLogxK
U2 - 10.1088/1475-7516/2013/11/021
DO - 10.1088/1475-7516/2013/11/021
M3 - Article
AN - SCOPUS:84888614498
SN - 1475-7516
VL - 2013
JO - Journal of Cosmology and Astroparticle Physics
JF - Journal of Cosmology and Astroparticle Physics
IS - 11
M1 - 021
ER -