What mass are the smallest protohalos?

TL;DR

The kinetic-decoupling temperature for weakly interacting massive particles (WIMPs) in supersymmetric (SUSY) and extra dimensional models that can account for the cold-dark-matter abundance determined from cosmic microwave background measurements is calculated.

Abstract

We calculate the kinetic-decoupling temperature for weakly interacting massive particles (WIMPs) in supersymmetric (SUSY) and universal-extra-dimension (UED) models that can account for the cold-dark-matter abundance determined from cosmic microwave background measurements. Depending on the parameters of the particle-physics model, a wide variety of decoupling temperatures is possible, ranging from several MeV to a few GeV. These decoupling temperatures imply a range of masses for the smallest protohalos much larger than previously thought -- ranging from 10^{-6} earth masses to 10^{2} earth masses. We expect the range of protohalos masses derived here to be characteristic of most particle-physics models that can thermally accommodate the required relic abundance of WIMP dark matter, even beyond SUSY and UED.

Figures (4)

• Figure 1: Neutralino-electron scattering cross section as a function of the electron energy $E_l$ for the four benchmark models A- D discussed in the text.
• Figure 2: Feynman diagrams contributing to the scattering of $\nu^{(1)}$ (a) and $B^{(1)}$ (b.1 and b.2) off leptons.
• Figure 3: The kinetic-decoupling temperature $T_{\rm kd}$ as a function of the WIMP mass for supersymmetric models (red empty dots are for the general MSSM while light-blue filled dots are for mSUGRA) giving a neutralino thermal relic abundance consistent with cosmology, and for UED models featuring a $B^{(1)}$ and a $\nu^{(1)}$ LKP. The four benchmark models A- D discussed in the text are also shown.
• Figure 4: The WIMP protohalo characteristic comoving wavenumber $k_c$ (left axis) and mass $M_c$ (right axis) as a function of the WIMP mass, for the same models as in Fig. \ref{['fig:mssm_ued_Tkd']}.