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We consider a possibility to explain the observed suppression of the secondacoustic 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 inthe standard Big Bang Nucleosynthesis (BBN). We estimate the required values ofthe cross-section-to-mass ratio for elastic scattering of CDM particles offbaryons. In case of velocity-independent elastic scattering (in the velocityinterval 10^{-5}--10^{-3}) we find that such particles do not contradictobservational limits if they are heavier than \sim 10^5 GeV or lighter than\sim 0.5 GeV. Another candidate, which may appear in the models with infiniteextra dimensions, is a quasistable charged particle decaying through tunnelinginto extra dimensions. Finally a millicharged particle with the electric chargeranging from \sim 10^{-4} to \sim 10^{-1} and with mass M\sim 0.1 GeV--1 TeValso may be responsible for the suppression of the second acoustic peak. As abyproduct we point out that CMB measurements set new limits on the allowedparameter space for the millicharged particles.Comment: 10 pages, 1 figur

Small second acoustic peak from interacting cold dark matter?