Classification of black holes in three dimensional spacetime by the W_(1+infty) symmetry

The BMS symmetry and related near horizon symmetry play important roles in holography in asymptotically flat spacetimes. They may also be crucial for solving the information paradox. But we still don't fully understand those infinite-dimensional symmetries. On the other hand, $W_{1+\infty}$ symmetry is the quantum version of area-preserving diffeomorphism of a plane. It is a dynamical symmetry of quantum Hall liquid and can be used to classify the quantum Hall universality classes. In this paper, we will show that the near horizon symmetry can be obtained from the $W_{1+\infty}$ symmetry. Based on this result, the black holes in three dimensional spacetime can be classified just as in the quantum Hall liquid. It also gives the result that the radius of black hole are quantized. This gives another evidence that our early claim "black hole can be considered as a kind of topological insulator" is correct.