Uncorrelated Compensated Isocurvature Perturbations from kSZ Tomography

TL;DR

This paper proposes a method using kSZ tomography to detect primordial compensated isocurvature perturbations with unprecedented sensitivity, surpassing current constraints significantly.

Contribution

It introduces a minimum-variance estimator leveraging independent measurements of galaxy and matter overdensities to detect CIPs.

Findings

Forecasts detectability of CIP amplitude as small as 5×10⁻⁹ with CMB-S4 and VRO.

Forecasts detectability of CIP amplitude as small as 1×10⁻⁷ with SO and DESI.

Current constraints on CIP amplitude are around 0.01.

Abstract

Compensated isocurvature perturbations (CIPs) are relative density perturbations in which a baryon-density fluctuation is accompanied by a dark matter density fluctuation such that the total-matter density is unperturbed. These fluctuations can be produced primordially if multiple fields are present during inflation, and therefore they can be used to differentiate between different models for the early Universe. Kinetic Sunyaev-Zeldovich (kSZ) tomography allows for the reconstruction of the radial-velocity field of matter as a function of redshift. This technique can be used to reconstruct the total-matter-overdensity field, independent of the galaxy-density field obtained from large-scale galaxy surveys. We leverage the ability to measure the galaxy- and matter-overdensity fields independently to construct a minimum-variance estimator for the primordial CIP amplitude, based on a mode-by-mode comparison of the two measurements. We forecast that a configuration corresponding to CMB-S4 and VRO will be able to detect (at $2\sigma$) a CIP amplitude $A$ (for a scale-invariant power spectrum) as small as $A\simeq 5\times 10^{-9}$. Similarly, a configuration corresponding to SO and DESI will be sensitive to a CIP amplitude $A\simeq 1\times 10^{-7}$. These values are to be compared to current constraints $A \leq {\cal O}(0.01)$.