Coolblue

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.

It contains a classification of hydrodynamic transport consistent with the existence of an entropy current. This involves developing new ideas on the emergence of the second law of thermodynamics and provides an effective field theory picture for relativistic hydrodynamics.


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