Cold dark matter: Controversies on small scales.

Area of Science:

• Cosmology
• Astrophysics
• Particle Physics

Background:

• The cold dark matter (CDM) model successfully explains large-scale cosmic structure.
• However, CDM faces challenges reconciling simulations with observations of small-scale structures, like dwarf galaxy satellites and dark matter halo cores.

Purpose of the Study:

• To review the observational and theoretical status of small-scale controversies in the CDM model.
• To explore potential resolutions involving baryonic physics and dark matter self-interactions.

Main Methods:

• Review of current cosmological simulations incorporating baryonic feedback (supernova feedback).
• Analysis of analytical models for dark matter self-interactions (elastic scattering).
• Examination of observational evidence from galaxy dynamics, gravitational lensing, and stellar halo streams.

Main Results:

• Simulations suggest baryonic feedback can resolve cusp-core and missing satellite problems in massive galaxies.
• Discrepancies persist in the lowest mass galaxies, questioning purely baryonic solutions.
• Dark matter self-interactions offer an alternative explanation, aligning halo profiles with observations.

Conclusions:

• Small-scale controversies highlight potential limitations of collisionless CDM.
• Baryonic physics and dark matter self-interactions are leading candidates for resolution.
• Future observations, particularly gravitational lensing and stellar halo studies, will further test these models.