Measuring the Angular Auto-power Spectrum of Fast Radio Burst Dispersion Measures as a Robust Cosmological Probe and Baryon Tracer

Fluctuations in the cosmic electron density are imprinted on the dispersion measures (DMs) of fast radio bursts (FRBs), making DMs a promising probe of cosmology and the spatial distribution of ionized baryons. In this work, we present the first measurement of the angular auto-power spectrum of FRB DMs, using 3455 apparently non-repeating bursts from the CHIME/FRB Catalog 2. We detect an angular correlation signal at >3 sigma significance, associated with large-scale electron-density fluctuations. By fitting the measured spectrum to theoretical models, we constrain two key parameter combinations: bh squared - H 0, which probes the cosmic baryon density and expansion rate, and bh squared - f d, which traces the baryon fraction in cosmic large-scale structure (LSS). We further assess the robustness of the power-spectrum method against systematic uncertainties arising from the assumed FRB redshift distribution and from the DM contributions of host galaxies (DM host), the Galactic halo (DM MW halo), and the Milky Way interstellar medium (DM MW ISM), using mock samples. Our results demonstrate that the angular power spectrum is largely insensitive to uncorrelated DM components such as DM host, thereby effectively mitigating the impact of poorly constrained host-galaxy systematics. In contrast to the traditional DM LSS - z relation, this method does not require individual redshift measurements--it relies only on the overall redshift distribution--and it partially breaks the parameter degeneracies in the bh squared - H 0 and bh squared - f d planes. These findings establish the DM angular power spectrum as a robust cosmological probe and a powerful baryon tracer.