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The nature of dark matter remains unknown, but upcoming measurements probingthe high-redshift Universe may provide invaluable insight. In the presence ofdark matter-baryon scattering, the suppression in the matter power spectrum andthe colder mean gas temperature are expected to modify the evolution of cosmicdawn and reionization. However, the contributions from such interactions to thebaryon and dark matter temperature perturbations have been neglected thus far.In this work, we derive these contributions, evolve the cosmologicalperturbations until the end of the dark ages and show that they may have asignificant impact in the beginning of cosmic dawn. In particular, we find thatthe amplitude of the temperature power spectrum at large scales can change byup to 1--2 orders of magnitude and that the matter power spectrum is furthersuppressed with respect to $\Lambda$CDM by $5$-$10\%$ at $k\sim 200\, {\rmMpc^{-1}}$ compared to the computation ignoring these contributions forscattering cross sections at current CMB limits. As a case example, we alsocompute the HI power spectrum from the dark ages, finding significantdifferences due to the changes in the temperature and ionization fraction powerspectra. We argue that these new contributions must be included in studies ofthis dark matter model relying on cosmic dawn and reionization observables.

Dark matter-baryon scattering effects on temperature perturbations and implications for cosmic dawn