• Rui-Yan Yu

      Articles written in Pramana – Journal of Physics

    • A new approach to two-charge fuzzball geometries

      Rui-Yan Yu

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      A few years ago, Mathur proposed a `fuzzball' conjecture to give a microscopic description of black hole entropy. In the fuzzball scenario, the entropy in a two-charge black hole corresponds to microstates of a two-charge string (brane) system, e.g., a winding fundamental string with momentum modes. The geometry of such a two-charge system is fuzzy near the horizon, and is very difficult to get analytically in general. In this paper, we show a new method to get geometries of two-charge fuzzball. Our method is based on the multipole expansion. We find that the method is powerful enough to get a clean analytic form of metric of the fuzzball with one-momentum mode. It is expected to get multi-mode geometries using this method in the near future.

    • Studying the cosmological apparent horizon with quasistatic coordinates

      Rui-Yan Yu Towe Wang

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      This article aims at a natural generalization of the static coordinates to the $(n + 1)$-dimensional Friedmann–Lemaître–Robertson–Walker (FLRW) Universe. After demonstrating a no-go theorem, we put forward the quasistatic coordinates for the FLRW Universe. Then, the quasistatic coordinates are utilized to study the unified first law and the scalar-type perturbations on the cosmological apparent horizon.

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