Self-Heating Dark Matter via Semiannihilation.

Area of Science:

• Cosmology
• Particle Physics
• Astrophysics

Background:

• Dark matter (DM) freeze-out depends on its temperature evolution.
• Kinetic equilibrium in DM requires sufficient elastic scattering, which may not always occur.
• Standard Model temperature evolution may not apply to DM.

Purpose of the Study:

• Investigate the temperature evolution of semiannihilating dark matter.
• Analyze the impact of semiannihilation on DM kinetic equilibrium and temperature.
• Explore the cosmological implications of this novel DM temperature evolution.

Main Methods:

• Studying the temperature evolution of semiannihilating dark matter.
• Analyzing the role of semiannihilation in maintaining kinetic equilibrium.
• Investigating the conversion of mass deficit to kinetic energy post freeze-out.

Main Results:

• Kinetic equilibrium is maintained by semiannihilation until late freeze-out stages.
• Semiannihilation drives a novel DM temperature evolution termed 'self-heating' after freeze-out.
• Self-heating DM suppresses structure formation on subgalactic scales, similar to warm DM.

Conclusions:

• Self-heating DM, with a large self-scattering cross section, can resolve discrepancies between cold dark matter predictions and observed subgalactic structures.
• This mechanism offers a unified solution to apparent failures of standard cold dark matter models.
• The flattened DM density profiles in inner halos due to self-scattering are a key prediction.