Inner structure of cold and warm dark matter halos from particle dynamics

Using the number of apocenter passages p and the radial action J(r) of each particle, we characterize the phase-space structure within the multi-stream regions of cold and warm dark matter halos in cosmological N-body simulations. Building on previous work by Enomoto, Nishimichi, and Taruya (2024, MNRAS, 527, 7523), we analyze the radial density profiles of particles classified by p and J(r). We find that the profiles consistently follow a double power-law structure, independent of the dark matter model or halo mass. The inner profile exhibits a rho proportional to r(-1) behavior, which is consistent with previous studies. Notably, these characteristics persist across both classification schemes. In contrast, the outer power-law profiles display distinct behaviors depending on the classification. While particles classified by p exhibit a steeper slope, ranging from -6 to -8, those classified by J(r) follow a common slope of approximately -3.5. Overall, the amplitude of the double power-law profiles varies between simulations for different dark matter models, but this variation can be attributed to statistical differences in the concentration of halos across the models.