Speaker1: Masaki Yamada (Tufts Univ.)
Title: On false vacuum decay catalyzed by black holes
False vacuum states are metastable in quantum field theories, and true vacuum bubbles can be nucleated due to the quantum tunneling effect. It was recently suggested that an evaporating Black Hole (BH) can be a catalyst of bubble nucleations and dramatically shortens the lifetime of the false vacuum. In particular, in the context of the Standard Model valid up to a certain energy scale, even a single evaporating BH may spoil the successful cosmology by inducing the decay of our electroweak vacuum. In this talk, we reinterpret catalyzed vacuum decay by BHs, using an effective action for a thin-wall bubble around a BH to clarify the meaning of bounce solutions. We calculate bounce solutions in the limit of a flat spacetime and in the limit of negligible backreaction to the metric, where it is much easier to understand the physical meaning, and compare these results with the full calculations done in the literature. As a result, we give a physical interpretation of the enhancement factor: it is nothing but the probability of producing states with a finite energy. This makes it clear that all the other states such as plasma should also be generated through the same mechanism, and calls for finite density corrections to the tunneling rate which tend to stabilize the false vacuum.

Speaker2: Ayuki Kamada (IBS)
Title: Galactic Rotation Curves with Dark Matter Self-Interactions
It has been shown that the LambdaCDM model can successfully explain large-scale structure of the universe. But it is not clear that it can accommodate observations on (sub-)galactic scales. In fact, the LambdaCDM model predicts dark matter halos, which are systematically denser than inferred from astrophysical observations. One interesting alternative assumes that dark matter particles are strongly interacting with each other. Dark matter self-interactions will lead to heat transfer from the hotter outer region to the cold inner region, reducing the central dark matter density. In this talk, I will show that the observed rotation curves of spiral galaxies are consistent with predicted in the SIDM model. I will also emphasize the importance of the baryonic disk in determining the SIDM halo profile.

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Last-modified: 2017-09-06 (水) 19:31:39 (75d)