Oscillator Level for Black Holes and Black Rings

Microscopic calculations of the Bekenstein-Hawking entropy of supersymmetric black holes in string theory are typically based on the application to a dual 2D CFT of Cardy's formula, S=2\pi \sqrt{c q /6}, where `c' is the central charge and `q' is the oscillator level. In the CFT, q is non-trivially related to the total momentum. We identify a Komar integral that equals q when evaluated at the horizon, and the total momentum when evaluated at asymptotic infinity, thus providing a gravitational dual of the CFT result.