Black hole thermodynamics, stringy dualities and double field theory

Understand

We discuss black hole thermodynamics in the manifestly duality invariant formalism of double field theory (DFT).

• We reformulate and prove the first law of black hole thermodynamics in DFT, using the covariant phase space approach.
• After splitting the full O(D, D) invariant DFT into a Kaluza-Klein-inspired form where only n coordinates are doubled, our results provide explicit duality invariant mass and entropy formulas.
• We illustrate how this works by discussing the black fundamental string solution and its T-duals.