MG14 - Talk detail

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Primordial inflation predicts generation of perturbations on comoving scales from roughly 1Gpc to 1m, if we assume the number of e-foldings during inflation is sixty as an example. Experiments related to Cosmic Microwave Background and Large Scale Structures have precisely determined primordial power on scales from roughly Gpc to Mpc. Primordial power on smaller scales is less understood, and there are several methods to constrain the amplitude of small-scale perturbations, one of which is dark matter minihalos. If primordial power on small scales is larger, more minihalos are formed earlier, which can survive to be present in our galaxy. In addition, if dark matter annihilates, resultant annihilation signals from minihalos can be substantial, since the density inside minihalos can be much larger than the typical dark matter density in our galaxy. Namely, observations of cosmic rays can be used to place upper bounds on the abundance of minihalos, and these upper bounds can then be translated into upper bounds on primordial power on small scales. These upper bounds depend on currently uncertain dark matter properties such as the mass or the annihilation cross section, or minihalo properties such as dark matter profile inside them. Previously, typical properties of dark matter and simple models of minihalos have been adopted to calculate upper bounds on small-scale perturbations, and so the dependence of upper bounds on these assumptions has been uncertain. We discuss how, and how much, upper bounds on small scale primordial perturbations depend on these assumptions for the first time, towards realistic use of minihalos as a potential tool to investigate primordial power on small scales.

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