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Area of Science:

  • Cosmology
  • Particle Physics
  • Astrophysics

Background:

  • The standard Lambda cold dark matter (ΛCDM) model faces challenges on small cosmological scales.
  • Dark matter self-interactions are a potential solution to these small-scale problems.

Purpose of the Study:

  • To investigate the implications of "puffy" dark matter, characterized by a finite size larger than its Compton wavelength.
  • To analyze how the velocity dependence of the self-interaction cross section in puffy dark matter affects cosmological models.

Main Methods:

  • Theoretical analysis of dark matter self-interaction cross sections.
  • Comparison of puffy dark matter velocity dependence with standard light-mediator models.
  • Exploration of a QCD-like theory for an explicit puffy dark matter example.

Main Results:

  • The self-interaction cross section of puffy dark matter decreases with velocity.
  • The velocity dependence is largely independent of the dark matter's internal structure.
  • Finite-size effects can dominate the velocity dependence, even with light mediators.

Conclusions:

  • Puffy dark matter offers a viable alternative for addressing small-scale ΛCDM issues.
  • Distinct observational signatures, particularly from direct-detection and indirect detection experiments, can differentiate puffy dark matter from other models.