Interacting photon–baryon fluid, warm dark matter, and the first acoustic peakJúlio C. Fabris, Alan M. Velasquez-Toribio, Winfried Zimdahl and Ilya L. ShapiroEur. Phys. J. C, 74 7 (2014) 2968DOI: https://doi.org/10.1140/epjc/s10052-014-2968-2