Probing Dark Energy Microphysics with kSZ Tomography

TL;DR

This paper explores how kSZ tomography combined with galaxy clustering can enhance constraints on dark energy's properties, especially its perturbations, beyond traditional background measurements.

Contribution

It demonstrates that kSZ tomography can significantly improve dark energy parameter constraints and probe its microphysical properties with future surveys.

Findings

kSZ tomography tightens constraints on dark energy parameters by up to 32%

Future surveys can detect dark-energy perturbations, especially with low sound speeds

Current measurements mainly test background expansion, future can probe microphysics

Abstract

The accelerated expansion of the Universe is well established by geometric probes, yet its physical origin remains poorly understood. Most constraints on dark energy arise from background observables -- supernovae, baryon acoustic oscillations, and the cosmic microwave background -- which mainly test the homogeneous expansion history. To move beyond this limitation, we examine how kinetic Sunyaev--Zel'dovich (kSZ) tomography, combined with galaxy clustering, can probe perturbative effects of dark energy and improve constraints on its background parameters. Using a Fisher-matrix analysis of the joint power spectra for LSST- and CMB-S4-like surveys, we quantify the additional information kSZ tomography contributes to dark-energy inference. Including kSZ data tightens constraints on $w_0$ by 15 % and on $w_a$ by 32 %, with parameter degeneracies distinct from those of geometric probes. We also assess the detectability of dark-energy perturbations through a two-parameter model, finding that for canonical sound speed ($c_s=1$) the effects are sub-percent and confined to horizon scales, while smaller sound speeds shift them to accessible $k$-ranges. Near-term kSZ measurements will primarily serve to test the consistency between background and perturbative signals, while future low-noise, high-resolution surveys may begin to uncover the microphysical properties of dark energy.