Uncorrelated compensated isocurvature perturbations from kinetic Sunyaev-Zeldovich tomography

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 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 compensated isocurvature perturbation (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 similar or equal to 5 x 10-9. Similarly, a configuration corresponding to SO and DESI will be sensitive to a CIP amplitude A similar or equal to 1 x 10-7. These values are to be compared to current constraints A <= O(0.01).

Automated summary

Compensated isocurvature perturbations (CIPs) refer to relative density fluctuations where baryon-density fluctuation is accompanied by a dark matter density fluctuation, keeping the total matter density unperturbed. By measuring the galaxy-density and matter-overdensity fields independently, a minimum-variance estimator for the primordial CIP amplitude can be constructed. Forecasts suggest that configurations such as CMB-S4 and VRO can detect CIP amplitudes as small as 5 x 10-9 under a scale-invariant power spectrum.