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The fine-scale structure of dark matter halos

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If you have a question about this talk, please contact Pau Figueras.

A wide range of astronomical observations indicate that cosmic structure formation is driven by the gravitational effects of dark matter. This contributes about 80 percent of the total cosmic mass budget and interacts extremely weakly with light and with all known forms of matter. It is most plausibly a new kind of elementary particle, yet to be detected directly or indirectly on Earth. At the time of recombination, 400,000 years after the Big Bang, the Universe was almost uniform, its only structure being weak linear fluctuations with statistical properties that can be inferred directly from observations of the cosmic microwave background. At this time dark matter particles had small thermal velocities and their distribution deviated from uniformity only through a gaussian field of density fluctuations with associated motions. Later evolution was driven purely by gravity and so obeyed the collisionless Boltzmann equation. This has immediate consequences for the present distribution of dark matter, even in extremely nonlinear regions such as the part of the Galaxy where the Sun resides. I will show how this structure can be followed in full generality in high-resolution N-body simulations by integrating the Geodesic Deviation Equation in tandem with the equations of motion, enhancing the effective resolution by more than 10 orders of magnitude and permitting a detailed treatment of annihilation radiation from dark matter caustics. I will also discuss how the predicted distribution at the Sun’s position impacts the expectations for terrestrial experiments seeking to detect the dark matter directly, in particular, the possibility of extremely narrow line signals that may be visible in axion detectors.

This talk is part of the Wednesday HEP-GR Colloquium series.

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