Effects of cold dark matter decoupling and pair annihilation on cosmological perturbations

By Edmund Bertschinger. 2006

156 citations recorded by the source corpus.

Weakly interacting massive particles (WIMPs) are part of the lepton-photon plasma in the early universe until kinetic decoupling, after which time the particles behave like a collisionless gas with nonzero temperature. The Boltzmann equation for WIMP-lepton collisions is reduced to a Fokker-Planck equation for the evolution of the WIMP distribution including scalar density perturbations. This equation and the Einstein and fluid equations for the plasma are solved numerically including the acoustic oscillations of the plasma before and during kinetic decoupling, the frictional damping occurring during kinetic decoupling, and the free-streaming damping occurring afterwards and throughout the radiation-dominated era. An excellent approximation reduces the solution to quadratures for the cold dark matter density and velocity perturbations. The subsequent evolution is followed through electron pair annihilation and the radiation-matter transition; analytic solutions are provided for both large and small scales. For a 100 GeV WIMP with bino-type interactions, kinetic decoupling occurs at a temperature T{sub d}=23 MeV. The transfer function in the matter-dominated era leads to an abundance of small cold dark matter halos; with a smooth window function the Press-Schechter mass distribution is dn/dlnM{proportional_to}M{sup -1/3} for M<10{sup -4}(T{sub d}/10 MeV){sup -3}M{sub {center_dot}}.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/7288b5eee32e7c6d09cb944e768fb59634e8c94d

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Citations in the corpus

Non-Abelian dark matter and dark radiation (2015, result): “This is in contrast with the more frequently studied case where the DM interactions freeze out at a critical temperature, leading to a sharp cutoff in the power spectrum at small scales [3, 21–23].”
Small-Scale Challenges to the ΛCDM Paradigm (2017, methodology): “In the standard WIMP paradigm, the lowmass end of the CDM hierarchy is set by first collisional damping (subsequent to chemical decoupling but prior to kinetic decoupling of the WIMPs), followed by free-streaming (e.g., Hofmann, Schwarz & Stöcker 2001; Bertschinger 2006).”
Halo mass function and the free streaming scale (2013, background): “Bertschinger (2006) assumed Tdk = 22.6 MeV, while Green et al. (2005) found Tdk = 33 MeV, based on slightly different assumptions.”
Hundreds of Milky Way Satellites? Luminosity Bias in the Satellite Luminosity Function (2008, background): “…extreme (larger than a factor of 1010) when compared to the full mass function of CDM subhalos, which is expected to rise as 1/M down to the small-scale clustering cutoff for the dark matter particle,McutT1M (Hofmann et al. 2001; Bertschinger 2006; Profumo et al. 2006; Johnson & Kamionkowski 2008).”
“Non-cold” dark matter at small scales: a general approach (2017, methodology): “is the theoretical subhalo mass function derived by an extended Press-Schechter approach [87, 88] based on a sharp-k window [89, 90].”
Hidden charged dark matter (2009, background): “[54, 55] to determine the temperature of kinetic decoupling for the dark matter particle.”
ETHOS - an effective theory of structure formation: dark matter physics as a possible explanation of the small-scale CDM problems (2015, result): “(7) This result for the evolved, non-linear power spectrum agrees to within about a factor of 2 with earlier analytic estimates for this regime (Loeb & Zaldarriaga 2005; Bertschinger 2006; Bringmann 2009), based on definitions ofMcut related to the form of the linear power spectrum.”