We discuss the possibility of producing a significant fraction of dark matter in the form of primordial black holes in the context of the pre-big bang inflationary scenario. We take into account, to this purpose, the enhancement of curvature perturbations possibly induced by a variation of the sound-speed parameter $c_s$ during the string phase of high-curvature inflation. After imposing all relevant observational constraints, we find that the considered class of models is compatible with the production of a large amount of primordial black holes in the mass range relevant to dark matter, provided the sound-speed parameter is confined in a rather narrow range of values, $0.003 < c_s < 0.01$.

中文翻译：

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大爆炸前暴胀的原始黑洞

我们讨论了在大爆炸前的暴胀情景中以原始黑洞的形式产生大量暗物质的可能性。为此，我们考虑了在高曲率膨胀的弦阶段可能由声速参数 $c_s$ 的变化引起的曲率扰动的增强。在施加所有相关的观测约束后，我们发现所考虑的模型类别与在与暗物质相关的质量范围内产生大量原始黑洞是兼容的，前提是声速参数被限制在相当窄的范围内值，$0.003 < c_s < 0.01$。