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The recent detection of the sky-averaged 21-cm cosmological signal indicatesa stronger absorption than the maximum allowed value based on the standardmodel. One explanation for the required colder primordial gas is the energytransfer between the baryon and dark matter fluids due to non-gravitationalscattering. Here, we explore the thermal evolution of primordial gas,collapsing to form Population III (Pop III) stars, when this energy transfer isincluded. Performing a series of one-zone calculations, we find that theevolution results in stars more massive than in the standard model, providedthat the dark matter is described by the best-fit parameters inferred from the21-cm observation. On the other hand, a significant part of the dark matterparameter space can be excluded by the requirement to form massive Pop IIIstars sufficiently early in cosmic history. Otherwise, the radiation backgroundneeded to bring about the strong Wouthuysen-Field coupling at z >~ 17, inferredto explain the 21-cm absorption feature, could not be builtup. Intriguingly,the independent constraint from the physics of first star formation at highdensities points to a similarly narrow range in dark matter properties. Thisexploratory study has to be followed-up with self-consistent three-dimensionalsimulations for a more rigorous derivation.

Baryon-dark matter scattering and first star formation