Cosmological Zero Modes

TL;DR

This paper introduces cosmological zero modes, a new class of primordial perturbations not described by power spectra, and explores their potential detection through CMB observations, revealing insights into the early universe beyond our horizon.

Contribution

It proposes and analyzes cosmological zero modes, including stochastic horizon perturbations and primordial monopoles, as novel non-perturbative primordial phenomena detectable via CMB.

Findings

White noise horizon perturbations constrained to amplitude $\, extless 9 imes 10^{-14}$.

Primordial monopoles detectable up to 11.6 times the horizon radius for charge Q.

Probes of zero modes can reveal non-perturbative early universe phenomena.

Abstract

We introduce a new family of primordial cosmological perturbations that are not described by traditional power spectra. At the linear level, these perturbations live in the kernel of the spatial Laplacian operator, and thus we call them cosmological zero modes. We compute the cosmic microwave background (CMB) temperature and polarization anisotropy induced by these modes, and forecast their detection sensitivity using a cosmic-variance limited experiment. In particular, we consider two configurations for the zero modes: The first configuration consists of stochastic metric perturbations described by white noise on a "holographic screen" located at our cosmological horizon. The amplitude of the power spectrum of this white noise can be constrained to be $\lesssim 9 \times 10^{-14}$. The second configuration is a primordial monopole beyond our cosmological horizon. We show that such a monopole, with "charge" $Q$, can be detected in the CMB sky up to a distance of $11.6 ~ Q^{1/4}\times$ horizon radius (or $160~ Q^{1/4}$ Gpc). More generally, observational probes of cosmological zero modes can shed light on non-perturbative phenomena in the primordial universe, beyond our observable horizon.