We consider the possibility of explaining the observed suppression of the second acoustic peak in the anisotropy spectrum of the cosmic microwave background (CMB) by interaction between a fraction of non-baryonic cold dark matter (CDM) and normal baryonic matter. This scenario does not require any modifications in standard big bang nucleosynthesis. We estimate the required values of the cross-section-to-mass ratio for elastic scattering of CDM particles off baryons. In the case of velocity-independent elastic scattering (in the velocity interval υ∼10-5-10-3) we find that such particles do not contradict observational limits if they are heavier than ∼105 GeV or lighter than ∼0.5 GeV. Another candidate, which may appear in the models with infinite extra dimensions, is a quasistable charged particle decaying through tunneling into extra dimensions. Finally, a millicharged particle with an electric charge ranging from ∼10-4 to ∼10-1 and with a mass M ∼0.1 GeV-1 TeV also may be responsible for the suppression of the second acoustic peak. As a by-product we point out that CMB measurements set new limits on the allowed parameter space for the millicharged particles.
ASJC Scopus subject areas
- Physics and Astronomy (miscellaneous)