Paths to Quantum Field Theory 2022

15 Aug 2022, 08:30 → 20 Aug 2022, 17:00 Europe/London

 

The workshop will take place in Durham, UK from 15th-20th of August. All talks will take place in Scott Logic Lecture Theater in the Mathematical Sciences/Computer Sciences building. The workshop is designed to bring a small number of expert speakers across the fields related to quantum field theory, including high-energy, nuclear and condensed matter physics, applying a range of techniques from numerical to theoretical and hybrid approaches. A typical day will consist of only two talks, with 2 hour slots available to to speakers to use as they wish. The idea of these loose time constraints is to encourage a slow pace, with a thorough introduction and to encourage questions and discussions during the talks, without much pressure of running out of time. The workshop will also be full of informal discussions. Further, we hope that a number of junior researchers will join as participants in discussing and posing insightful questions.

 

Link to the YouTube channel: https://www.youtube.com/playlist?list=PLj3thPoeBSKy1TjhlI1TdTNqstCvsT_1h

 

Confirmed speakers:

Sean Hartnoll
Zohar Komargodski
Srimoyee Sen
Yi-Zhuang You
John McGreevy
Olexei Motrunich
Julian Sonner
Sid Parmeswaran
Kedar Damle 

 

Organizers

Costas Bachas
Iñaki García Etxebarria
Nabil Iqbal
Max Metlitski
Anders Sandvik
Tin Sulejmanpasic
David Tong

>> Special thanks to Trish Parkin and Lucca Fazza for administrative and technical support <<

 

Monday, 15 August

08:30 Registration/Coffee/Welcome

1 Quantum gravity and quantum chaos - Julian Sonner

12:00 Lunch and Discussion

2 Studies of Deconfined Quantum Criticality in One-Dimensional Spin Chains - Olexei Motrunich

I will describe our studies of possible realizations of deconfined quantum critical points (DQCP) in one-dimensional (1d) spin chains. I will first present a spin-1/2 chain with Z2 x Z2 symmetry that shows continuous transition between an Ising ferromagnet (FM) and a Valence Bond Solid (VBS) phase. Many aspects of this transition resemble proposed DQCP physics in two-dimensional (2d) spin models with easy-plane symmetry, while the 1d setting allows for controlled and complete field-theoretic description of the transition. I will then present a spin-1 chain with Z3 x Z3 symmetry where our extensive numerical studies suggest a continuous transition between a Z3 ferromagnet and a VBS phase, and I will describe some theoretical attempts to describe this transition. Further, we find a special point on the FM-VBS phase boundary where the model happens to be integrable with some properties known exactly. It turns out that the integrable point has a minuscule gap and an extremely long correlation length of about 200000 lattice spacings, well beyond the reach of our numerics. We hence conjecture that the Z3 x Z3 FM-VBS transition is extremely weakly first order and discuss a walking RG interpretation of the origin of this behavior, resembling some interpretations for very weak first-order DQCP transitions in 2d spin models. I will conclude with some lessons and open questions from our studies.

Tuesday, 16 August

09:00 Coffee and Discussion

3 Renormalization group flows on line defects and one-form symmetry - Zohar Komargodski

12:00 Lunch and Discussion

4 Winding theta and semiclassical destructive interference - Mendel Nguyen

15:00 Discussion/Break

5 Yuya Tanizaki

16:00 Discussion/Break

6 Chiral Gauge Dynamics: Candidates for Non-Supersymmetric Dualities - Kaan Onder

I will describe our study of the dynamics of chiral SU(N) gauge theories. These contain Weyl fermions in the symmetric or anti-symmetric representation of the gauge group, together with further fermions in the fundamental and anti-fundamental. I will recap an old proposal of Bars and Yankielowicz who match the ’t Hooft anomalies of this theory to free fermions. I will then show that there are novel and, in some cases, quite powerful constraints on the dynamics in the large N limit. In addition, I will describe these SU(N) theories with an extra Weyl fermion transforming in the adjoint representation. Here I will show that all 21 ’t Hooft anomalies for global symmetries are matched with those of a Spin(8) gauge theory. This suggests a non-supersymmetric extension of the duality of Pouliot and Strassler.

Wednesday, 17 August

09:00 Coffee/Discussion

7 Gauss Law Entanglement in Matrix Quantum Mechanics. - Sean Hartnoll

It is well-established the local quantum field theories can arise from lattice models. A distinct origin of quantum fields are large N matrices where, in contrast to most lattice models, no locality is manifest in the microscopic Hamiltonian. The emergence of locality from matrix theories is not well-understood. One diagnostic of locality is (emergent) area law entanglement of the microscopic degrees of freedom. I will discuss a particularly robust notion of entanglement in matrix theories that is rooted in their U(N) Gauss law constraint. I will describing forthcoming work in which we compute this entanglement in a particular model of an emergent fuzzy sphere, demonstrating the presence of area-law entanglement.

12:00 Lunch/Discussion

8 CANCELLED - Sid Parmeswaran

Thursday, 18 August

09:00 Coffee/Discussion

9 Generalized Hall current for gapless defect fermions - Sri Sen

I generalize the idea of the quantized Hall current to count gapless edge states in topological materials in any number of dimensions. This construction applies equally well to theories without any continuous symmetries in the bulk or chiral anomalies on the boundaries. The generalized Hall current is related to the phase space index of the Euclidean fermion operator and can be calculated via one-loop Feynman diagrams. The relevant momentum-space topology is shown to be governed in each case by the nth homotopy group of sphere where n is the number of space-time dimensions. I elucidate these ideas by explicit examples in free relativistic field theories in various spacetime dimensions with various symmetries

12:00 Lunch/Discussion

10 BF theory in TFTs from string theory - Saghar Hosseini

(d+1)-dimensional topological field theories (TFTs) encode the higher symmetries, 't Hooft anomalies, higher structures, and the BF theory of d-dimensional quantum field theories. These theories may be obtained from string theory by dimensional reduction. I will discuss how the BF theory, realising all the possible choices of higher symmetries, can be found by constructing a Chern-Simons action for the self-dual field in supergravity.

15:00 Discussion/Break

11 Charged spinning operators in CFTs: from superfluids to Regge theory - Gabriel Francisco Cuomo

It has been recently understood that, in CFT, states with large quantum numbers often admit a simple universal description. Most famously, CFTs become approximately free in the large spin sector, with operators organized in Regge trajectories labeled by the twist. On the other hand, operators with large quantum numbers under the internal symmetries of the theory often admit an effective hydrodynamic description. In this talk, I will review these results and I will propose a series of EFT descriptions for operators with both large charge and large spin in 3d CFTs. The results smoothly interpolate between the hydrodynamic regime and the large spin Regge theory.

16:00 Discussion/Break

12 Hawking radiation on the lattice as universal (Floquet) quench dynamics - Nick Bultinck

I will present two elementary free fermion lattice models which exhibit Hawking radiation in quench dynamics. Due to their simplicity, the origin of the Hawking particles in these Lorentz-violating models is particularly clear: Hawking radiation is the result of simple scattering processes of electrons deep inside the Fermi/Dirac sea of the vacuum.

Friday, 19 August

09:00 Coffee/Discussion

13 Symmetric Mass Generation - Yi-Zhuang You

Symmetric mass generation (SMG) is a novel mechanism for massless fermions to acquire a mass via a strong-coupling non-perturbative interaction effect. In contrast to the conventional Higgs mechanism for fermion mass generation, the SMG mechanism does not condense any fermion bilinear coupling and preserves the full symmetry. It is connected to a broad range of topics, including anomaly cancellation, topological phase classification, and chiral fermion regularization. In this talk, I will introduce SMG through toy models, and review the current understanding of the SMG transition. I will also mention recent numerical efforts to investigate the SMG phenomenon. I will conclude the talk with remarks on future directions.

12:00 Lunch/Discussion

14 Local symmetric quantum systems have new conservation laws - Hanqing Liu

One of the most important implications of continuous symmetry in a physical system is the existence of conservation laws, which holds irrespective of whether the theory is local or not. On the other hand, while locality can, for example, lead to the Lieb-Robinson bound on the propagation speed of information, it does not impose any conservation laws without symmetry. Therefore, it is very natural and interesting to ask, in the presence of symmetry, does locality lead to any additional conservation laws? Surprisingly, the answer is yes. In this talk, I will show that such new conservation laws exist in systems with 2-local interactions and SU(d) symmetry for d≥3. I will explain how these new conservation laws arise and give some simple examples.

15:00 Discussion/Break

15 Renormalisation and discrete-scale invariance in a classical dimer model - Sounak Biswas

We introduce the classical dimer model on the quasiperiodic Ammann-Beenker (AB) graph, which has an unusual property that the dimer-constraint is exactly reproduced at successive discrete scales; this seeds effective dimer models at different scales--- leading to an unusually rich structure of slowly decaying dimer correlations. Here, we explicitly construct a real-space renormalisation group transformation and show, using extensive Monte Carlo simulations, that it produces a fixed point of the dimer distributions. We also use this transformation to extract the fixed-point Hamiltonian of dimers. Our results provide concrete evidence of a classical statistical mechanical model whose properties are controlled by a fixed point with discrete scale invariance.

16:00 Discussion/Break

16 Islands in AdS/ICFT - Pietro Pelliconi

Large black holes in anti-de Sitter space have positive specific heat and do not evaporate. In order to mimic the behavior of evaporating black holes, one may couple the system to an external bath. We explore a rich family of such models, namely ones obtained by coupling two holographic CFTs along a shared interface (ICFTs). We focus on the limit where the bulk solution is characterized by a thin brane separating the two individual duals. These systems may
be interpreted in a double holographic way, where one integrates out the bath and ends up with a lower-dimensional gravitational braneworld dual to the interface degrees of freedom. Our setup has the advantage that all observables can be defined and calculated by only relying on standard rules of AdS/CFT. We exploit this to establish a number of general results, relying on a detailed analysis of the geodesics in the bulk. We prove that the entropy of Hawking radiation in the braneworld is obtained by extremizing the generalized entropy, and moreover that at late times a so-called ‘island saddle’ gives the dominant contribution.

Saturday, 20 August

09:00 Coffee/Discussion

17 Kedar Damle

12:00 Lunch/Discussion

18 Entanglement Bootstrap and Remote Detectability - John McGreevy (online)

The Entanglement Bootstrap is a program to derive the universal properties of a phase of matter from a single representative wavefunction on a simply-connected domain. Much (perhaps all) of the structure of topological quantum field theory can be extracted starting from a state satisfying two axioms that implement the area law for entanglement. This talk will focus on recent progress (with Bowen Shi and Jin-Long Huang) using this approach to understand remote detectability of topological excitations in various dimensions. This is an axiom of topological field theory. Two key ideas are a quantum avatar of Kirby's torus trick to construct states on closed manifolds, and the new concept of pairing manifold, which is a closed manifold associated with a pair of conjugate excitation types that encodes their S-matrix. The pairing manifold also implies Verlinde formulae relating the S-matrix to the structure constants of an algebra of flexible operators.