## Summary

Quantum gravity; Quantum field theory; String theory; Black holes

## Research Focus

My research is on quantum gravity and quantum field theory, using techniques from string theory, general relativity, condensed matter, and quantum information.

*Emergent Spacetime*

Recent advances in string theory and quantum gravity suggest that spacetime, and the laws of gravity that govern it, are ‘emergent’ phenomena, resulting from the collective behavior of an enormous number of unknown degrees of freedom. This idea underlies gauge/gravity duality, which is an exact relation between quantum gravity and a lower-dimensional quantum field theory. One goal of my research is to understand how the degrees of freedom in a quantum field theory reorganize themselves into a fluctuating spacetime, and to use gauge/gravity duality as a model for a more complete theory of quantum gravity.

*Black Hole Thermodynamics*

Black holes play an important role in quantum gravity because they can be viewed in two very different ways: as classical solutions of general relativity, or as quantum, statistical systems obeying the laws of the thermodynamics. I am exploring this relationship in various contexts, including 3d gravity, semi-realistic Kerr black holes, and string theory.

*New Approaches to Quantum Field Theory*

The connections between gravity and quantum field theory have also led to important new insights in quantum field theory. For example, the absorption of photons by a black hole can be used to calculate conductivity in certain strongly coupled field theories where other methods break down. I am using related techniques to study phase transitions, entanglement, renormalization group flows, and other phenomena in quantum field theory.

*The Physics of de Sitter Space*

Ultimately, quantum gravity must be tested by experiment. Early universe cosmology is perhaps the most likely place for this to happen, since both gravitational and quantum effects are important. It is possible that fundamentally new ideas are needed to understand this regime, so I am working on new approaches to inflation and the physics of de Sitter space inspired by gauge/gravity duality.

**Graduate Students**

Ryan Bilotta and Yikun Jiang

## Publications

A. Almheiri, T. Hartman, J. Maldacena, E. Shaghoulian, and A. Tajdini, "Replica wormholes and the entropy of Hawking radiation," JHEP05 (2020) 013, arXiv:1911.12333

T. Hartman, S. Jain, S. Kundu, “Causality Constraints in Conformal Field Theory,” JHEP 2016:99, arXiv: 1509.00014.

T. Faulkner, M. Guica, T. Hartman, R. C. Myers, M. Van Raamsdonk, “Gravitation from Entanglement in Holographic CFTs,” JHEP **1403 **(2014) 051 arXiv: 1312.7856.

T. Hartman, J. Maldacena, “Time Evolution of Entanglement Entropy from Black Hole Interiors,” JHEP **1305** (2013) 014 arXiv: 1303.1080.

M. Guica, T. Hartman, W. Song, A. Strominger, “The Kerr/CFT Correspondence,” Phys. Rev. D**80** (2009) 124008 arXiv:0809:4266 [hep-th].