Constraining cosmological ultra-large scale structure using numerical relativity

Abstract

Cosmic inflation, a period of accelerated expansion in the early universe, can give rise to large amplitude ultra-large scale inhomogeneities on distance scales comparable to or larger than the observable universe. The cosmic microwave background (CMB) anisotropy on the largest angular scales is sensitive to such inhomogeneities and can be used to constrain the presence of ultra-large scale structure (ULSS). We numerically evolve nonlinear inhomogeneities present at the beginning of inflation in full General Relativity to assess the CMB quadrupole constraint on the amplitude of the initial fluctuations and the size of the observable universe relative to a length scale characterizing the ULSS. To obtain a statistically significant number of simulations, we adopt a toy model in which inhomogeneities are injected along a preferred direction. We compute the likelihood function for the CMB quadrupole including both ULSS and the standard quantum fluctuations produced during inflation. We compute the posterior given the observed CMB quadrupole, finding that when including gravitational nonlinearities, ULSS curvature perturbations of order unity are allowed by the data, even on length scales not too much larger than the size of the observable universe. Our results illustrate the utility and importance of numerical relativity for constraining early universe cosmology.

14 pages, 6 figures v3: Clarifications added regarding the generality of results - conclusions unchanged, version accepted for publication in PRD, v2: updated with minor clarifications, submitted

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• The Effects of Potential Shape on Inhomogeneous Inflation
• Inflationary Butterfly Effect: Non-perturbative Dynamics From Small-Scale Features
• Starting inflation from inhomogeneous initial conditions with momentum
• Mathematical General Relativity
• Cosmology using numerical relativity
• Einstein-Vlasov Calculations of Structure Formation
• A numerical relativity scheme for cosmological simulations
• Robustness of inflation to kinetic inhomogeneities
• Structure formation and quasi-spherical collapse from initial curvature perturbations with numerical relativity simulations
• EBWeyl: a Code to Invariantly Characterize Numerical Spacetimes
• Cosmological Zero Modes
• Topology of Cosmological Black Holes