Status of Cold Dark Matter Cosmology
Joel R. Primack
TL;DR
The paper surveys the status of Cold Dark Matter cosmology, arguing that $\Lambda$CDM with $\Omega_m \approx 0.3$, $\Omega_\Lambda \approx 0.7$, and $h \approx 0.7$ provides a robust fit to large-scale observations (CMB, clusters, Ly$\alpha$ forest) and successfully reproduces galaxy statistics via N-body simulations and semi-analytic models. It reviews small-scale tensions—particularly halo-center cusps, substructure, and angular momentum of baryons—and discusses how baryonic physics and measurement biases can alleviate many concerns, though some issues may persist. The author evaluates alternatives such as SIDM and WDM, finding they introduce new problems and are not clearly favored, while a tilt in the primordial power spectrum (e.g., $n \approx 0.9$) offers a promising direction. Overall, $\Lambda$CDM remains the best-supported framework given current data, but inner-halo physics and possible refinements will require further observational and theoretical work.
Abstract
Cold Dark Matter (CDM) has become the standard modern theory of cosmological structure formation. Its predictions appear to be in good agreement with data on large scales, and it naturally accounts for many properties of galaxies. But despite its many successes, there has been concern about CDM on small scales because of the possible contradiction between the linearly rising rotation curves observed in some dark-matter-dominated galaxies vs. the $1/r$ density cusps at the centers of simulated CDM halos. Other CDM issues on small scales include the very large number of small satellite halos in simulations, far more than the number of small galaxies observed locally, and problems concerning the angular momentum of the baryons in dark matter halos. The latest data and simulations have lessened, although not entirely resolved, these concerns. Meanwhile, the main alternatives to CDM that have been considered to solve these problems, self-interacting dark matter (SIDM) and warm dark matter (WDM), have been found to have serious drawbacks.