## Research

I'm interested in physics related to string theory, quantum gravity, holography. A recurring theme in my research is thermality and various notions of entropy. Here are some of the topics that I am currently thinking about (click keywords to expand):

**Bulk emergence from entanglement**

Based on the Ryu-Takayanagi formula and many subsequent developments, it is known that correlations (such as entanglement) between CFT degrees of freedom provide a crucial feature for having a dual description in terms of semi-classical gravity in AdS. I am working on furthering our understanding of the precise mechanism by which a gravitational description (and quantum corrections to it) emerge in this context. I am also interested in identifying other quantum information theoretic quantities that teach us interesting new things about gravity, holography, and black holes.
**Quantum chaos**

Classical chaos is associated with the butterfly effect at early times and notions of ergodicity at late times. I am interested in quantum versions of these phenomena. One way to characterize quantum chaos is by means of the early time behavior of out-of-time-order correlation functions. Their precise structure serves both as a diagnostic of black hole physics in CFTs, as well as a tool to understand quantum aspects of gravity in holographic theories. Among other things, I am developing a simple effective field theory for the physics of energy-momentum exchange and quantum chaos in CFTs with many degrees of freedom.
**Hydrodynamics and the emergence of entropy**

Hydrodynamics provides a coarse-grained description of quantum states in local thermal equilibrium. It has only recently become clear how to think about hydrodynamics as a genuine effective field theory of low-energy degrees of freedom. Crucially, we found that there are universal emergent symmetries (in fact, a particular supersymmetry that encodes constraints from unitarity and thermality). These provide novel degrees of freedom (such as BRST ghosts) and constraints to write a consistent real-time effective action of dissipative hydrodynamics. I am interested in using AdS/CFT for holographic fluids in order to understand what these statements teach us about dissipation, entropy and the black hole interior.
#### Publications

For details on all of my publications, visit
Inspire or arXiv. Here is a selection:

**◊ Effective Field Theory for Chaotic CFTs**

(FH, M. Rozali)

JHEP 1810 (2018) 118 [arXiv:1808.02898]

**◊ An Inflow Mechanism for Hydrodynamic Entropy**

(FH, R. Loganayagam, M. Rangamani)

Phys. Rev. Lett. 121, 051602 [arXiv:1803.08490]

**◊ Nonlinear Gravity from Entanglement in CFTs**

(T. Faulkner, FH, E. Hijano, O. Parrikar, C. Rabideau,

M. Van Raamsdonk)

JHEP 1708 (2017) 057 [arXiv:1705.03026]

**◊ Entanglement, Holography and Causal Diamonds**

(J. de Boer, FH, M. Heller, R. Myers)

JHEP 1608 (2016) 162 [arXiv:1606.03307]

**◊ The Fluid Manifesto: Emergent Symmetries, Hydrodynamics,
and Black Holes**

(FH, R. Loganayagam, M. Rangamani)

JHEP 1601 (2016) 184 [arXiv:1510.02494]

**◊ Adiabatic hydrodynamics: The Eightfold Way to Dissipation**

(FH, R. Loganayagam, M. Rangamani)

JHEP 1505 (2015) 060 [arXiv:1502.00636]

#### PhD thesis

My PhD thesis can be found here.

#### Related

◊ The website of the Simons Collaboration 'It from Qubit' describes

research that I am either working on, or following with interest.

◊ An easy-to-read article about some topics of interest to me

◊ String Theory Group at UBC