Dynamical Test of Cosmic Acceleration: k-nearest Neighbor Cross Correlation of Cosmic Microwave Background and Cosmic Infrared Background

The physical origin of cosmic acceleration remains one of the central questions in modern cosmology. The integrated Sachs-Wolfe (ISW) and Rees-Sciama (RS) effects, which arise from the evolution of gravitational potentials, provide a dynamical test of cosmic acceleration. We measure the cross correlation between the Planck temperature map of the cosmic microwave background (CMB) and a foreground-free map of the 100, mu m cosmic infrared background (CIB) from Y.-K. Chiang (2023), using the k-nearest neighbor cumulative distribution function (k NN-CDF). As the CIB map is reconstructed from about 600 million Wide-field Infrared Survey Explorer galaxies extending to z about2.5, the measurement is equivalent to a galaxy-CMB cross correlation. We find evidence for a positive cross correlation, rejecting the null hypothesis of no correlation at p=0.02 (2.3 sigma) using the chi squared test. We further quantify its amplitude with A k NN, defined relative to an assumed cosmological model, and obtain A k NN=0.95 plus or minus0.20 (4.8 sigma) with respect to CDM mock data including the ISW and RS effects. The k NN-CDF analysis improves the detection significance by about 20% over the two-point correlation function. We also explore evolving dark energy by constructing two tomographic maps from the full CIB map; the results are consistent with CDM. Finer tomographic reconstruction of the CIB, for example from multiband data of SPHEREx, would further tighten constraints on evolving dark energy.