Imprints of Primordial Voids on the CMB

Abstract

We generalize in several ways the results existing in the literature: a) we make use of an exact general relativistic solution for a spherical, nearly empty cavity in the matter dominated era to evaluate the null geodesics and the Sachs-Wolfe effect; b) we evaluate the magnitude of the adiabatic fluctuations of the photon-baryon plasma; c) we study the influence of the shell profile; and d) we take into account the finite thickness of the last scattering surface (LSS) and the influence of its position with respect to the void center. We find empirically an analytic approximation to the Sachs-Wolfe effect for all crossing geometries and we derive an upper limit of $\approx$ 25 $h^{-1}$ Mpc for the comoving radii of voids sitting on the LSS in order to achieve compatibility with COBE's data. As a nearly empty void has an overcomoving expansion of a factor of $\approx$ 4 between decoupling and the present, the maximum allowed size at present is $\approx$ 100 $h^{-1}$ Mpc. On the other hand, the smallness of the comoving size relative to the sound horizon reduces strongly the adiabatic effect by Silk damping and makes it negligible. Most of the signature of primordial voids comes therefore from metric effects and consists of subdegree spots blue or red depending on whether the center lies beyond or within the LSS. In conclusion we refine and confirm earlier constraints on a power law void spectrum originated in an inflationary phase transition and capable of generating the observed large scale structure.

14 pages, 5 figures, submitted to Montly Notices

Cited by in corpus (14)

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• "Graceful" Old Inflation
• Effect of Void Network on CMB Anisotropy
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• Spatial and temporal tuning in void models for acceleration
• Constraining CMB-consistent primordial voids with cluster evolution
• Sub-degree CMB anisotropies from inflationary bubbles
• Effects of inflationary bubbles on the polarization and temperature anisotropies of the cosmic microwave background
• Present limits to cosmic bubbles from the COBE-DMR three point correlation function
• Quantifying galactic clustering and departures from randomness of the inter-galactic void probability function using information geometry
• Wavelet analysis of non-Gaussian anisotropies from primordial voids in simulated maps of the Cosmic Microwave Background
• Phenomenological aspects of dark energy dominated cosmologies
• Cosmic voids and BAO with relative baryon-CDM perturbations