Name: Nonperturbative Methods in Quantum Field Theory
Start: 2022-05-23T09:00:00+02:00
End: 2022-06-03T19:00:00+02:00
Location: CERN

Nonperturbative Methods in Quantum Field Theory

from Monday, May 23, 2022 (9:00 AM) to Friday, June 3, 2022 (7:00 PM)

Monday, May 23, 2022

9:30 AM Coffee Break
Coffee Break
9:30 AM - 10:00 AM
10:00 AM Attacking the Sinh-Gordon model with relativistic continuous matrix product states* - Antoine Tilloy (Mines ParisTech)
Attacking the Sinh-Gordon model with relativistic continuous matrix product states*
- Antoine Tilloy (Mines ParisTech)
10:00 AM - 11:00 AM
Room: 503/1-001 - Council Chamber The Sinh-Gordon model is a 1+1 dimensional quantum field theory with a potential cosh(b phi) that is quite peculiar. It is at the same time exactly solvable (for many observables) and not well understood. I will present the results of a variational exploration of its strong coupling regime with a recent generalization of continuous matrix product states. The advantage of this method is that it does not require introducing a cutoff, UV or IR, is fully non-perturbative, typically converges fast for Hamiltonians with polynomial interactions, and gives rigorous energy upper bounds. Its application to the Sinh-Gordon model is only partly successful: observables can be computed accurately up to fairly large values of the coupling, but the ultra strong coupling regime remains difficult to access without extrapolations. As a result, the behavior near the self-dual point is not yet fully settled. I will show the basics of relativistic continuous matrix product states, explain how they typically work for phi^4 like theories or even the easier Sine-Gordon model and finally discuss my attempts at taming Sinh-Gordon.
12:00 PM Lunch
Lunch
12:00 PM - 2:00 PM
2:00 PM Renormalons from Integrability: A resurgent insight into QFT's conundrum* - Tomas Reis (University of Geneva)
Renormalons from Integrability: A resurgent insight into QFT's conundrum*
- Tomas Reis (University of Geneva)
2:00 PM - 3:00 PM
Room: 503/1-001 - Council Chamber Renormalons are non-perturbative effects which are manifested in perturbative series. While they figure in asymptotically free field theories including both QCD and some integrable models, they are in general poorly understood. In this talk I will present results on how to analytically find these non-pertubative effects in the free energy of integrable models. These effects turn out to defy standard expectations which went back to Parisi and ’t Hooft. I will also present a short introduction to the framework of resurgence and to how it is a key tool in the analysis of non-perturbative effects in QFT.
3:30 PM Coffee Break
Coffee Break
3:30 PM - 4:00 PM
Tuesday, May 24, 2022

9:30 AM Coffee Break
Coffee Break
9:30 AM - 10:00 AM
10:00 AM Hamiltonian truncation in AdS* - Matthijs Hogervorst (EPFL)
Hamiltonian truncation in AdS*
- Matthijs Hogervorst (EPFL)
10:00 AM - 11:00 AM
Room: 503/1-001 - Council Chamber Anti-de Sitter spacetime is interesting for many reasons: of course it furnishes a canvas for the study of quantum gravity, but it also appears to be a fruitful setting for Hamiltonian truncation. After all, QFTs in AdS have a notion of conserved energy, their Hilbert spaces are well-understood, and even a hard energy cutoff preserves many spacetime symmetries. In this talk I will discuss this framework in detail and present some results on both scalar fields and 2d minimal models. In particular, I will discuss the issue of divergent counterterms that arise from the curvature of AdS, and present a prescription to extract the correct continuum limit. Based on work with M. Meineri, J. Penedones and K. Salehi Vaziri, arXiv:2104.10689. An introductory example in Python can be found at the attached link.
12:00 PM Lunch
Lunch
12:00 PM - 2:00 PM
2:00 PM Torus Spectroscopy: A novel numerical tool to diagnose the nature of quantum phase transitions and quantum spin liquids - Andreas Laüchli (PSI / EPFL)
Torus Spectroscopy: A novel numerical tool to diagnose the nature of quantum phase transitions and quantum spin liquids
- Andreas Laüchli (PSI / EPFL)
2:00 PM - 3:00 PM
Room: 503/1-001 - Council Chamber In this talk I will present the torus spectroscopy, i.e. the analysis of the finite volume spectrum of the Hamiltonian on a spatial torus in 2+1D as a practical numerical tool to determine the universality class of quantum phase transitions. We show an application with an emergent 3D O(2) phase transition and that we are able to detect the presence of dangerously irrelevant couplings. In a second application we report on ongoing work to shed light on the possible presence of a QED$_3$ like phase (Dirac spin liquid) in a frustrated spin model.
3:30 PM Coffee Break
Coffee Break
3:30 PM - 4:00 PM

4:00 PM Structured Discussion
Structured Discussion
4:00 PM - 5:30 PM
Room: 503/1-001 - Council Chamber
Wednesday, May 25, 2022

9:30 AM Coffee Break
Coffee Break
9:30 AM - 10:00 AM
10:00 AM Hydrodynamization, asymptotics and the early to late time interpolation in relativistic hydrodynamics* - Inês Aniceto (University of Southampton)
Hydrodynamization, asymptotics and the early to late time interpolation in relativistic hydrodynamics*
- Inês Aniceto (University of Southampton)
10:00 AM - 11:00 AM
Room: 503/1-001 - Council Chamber Dissipative relativistic hydrodynamics is expected to describe the late times, thermalised behaviour of strongly coupled fluids such as a strongly coupled super Yang-Mills plasma. These systems are then accurately described by a hydrodynamic series expansion in small gradients. Surprisingly, this hydrodynamic expansion is accurate even when the systems are still quite anisotropic: the non-hydrodynamic modes governing the non-equilibrium behaviour at very early-times become exponentially close to the hydrodynamic solution in an early process called hydrodynamization. This early success is intimately related with the fact that the hydrodynamic expansion is asymptotic. The theory of transseries and resurgence explicitly shows how the non-hydrodynamic modes are in fact encoded in this late-time expansion. In this talk we will focus on a MIS-type model and use exponentially accurate summations of the the late-time resurgent transseries to recover the behaviour of the fluid before hydrodynamisation, and effectively match it to any given initial non-equilibrium condition. We will further show that such summations can provide analytic predictions beyond the late time regime.
12:00 PM Lunch
Lunch
12:00 PM - 2:00 PM

2:00 PM No Talk Scheduled (CERN Theory Colloquium)
No Talk Scheduled (CERN Theory Colloquium)
2:00 PM - 3:00 PM

3:30 PM Coffee Break
Coffee Break
3:30 PM - 4:00 PM
4:00 PM Hamiltonian truncation for real time dynamics in (gauge) QFT* - Ivan Kukuljan (Max Planck Institute for Quantum Optics)
Hamiltonian truncation for real time dynamics in (gauge) QFT*
- Ivan Kukuljan (Max Planck Institute for Quantum Optics)
4:00 PM - 5:00 PM
Room: 503/1-001 - Council Chamber Hamiltonian truncation methods represent a powerful toolbox for a set of problems that are otherwise very challenging in strongly coupled quantum field theory: nonequilibrium physics and real time evolution. In many such cases analytical approaches are limited as well as numerical tools like lattice gauge theory and tensor networks. I will talk about recent developments in this field with emphasis to entanglement properties of QFT, connection to ultra cold atomic simulators and exploring new fundamental phenomena.
Thursday, May 26, 2022

9:30 AM Coffee Break
Coffee Break
9:30 AM - 10:00 AM
10:00 AM Hamiltonian Truncation and Effective Field Theory* - Kara Farnsworth (Case Western Reserve University)
Hamiltonian Truncation and Effective Field Theory*
- Kara Farnsworth (Case Western Reserve University)
10:00 AM - 11:00 AM
Room: 500/1-001 - Main Auditorium Hamiltonian truncation is a non-perturbative numerical method for calculating observables of a quantum field theory by truncating the Hilbert space to states with energy below a maximum energy cutoff. In this talk I will present an effective field theory approach to Hamiltonian truncation, which provides a systematic way of improving the calculations without increasing the energy cutoff. I will demonstrate this with numerical results for the two dimensional phi^4 theory, and talk about future applications of this method to more complicated theories.
12:00 PM Lunch
Lunch
12:00 PM - 2:00 PM
3:00 PM Thermalization and Chaos in 1+1d QFTs - Luca Delacrétaz (University of Chicago)
Thermalization and Chaos in 1+1d QFTs
- Luca Delacrétaz (University of Chicago)
3:00 PM - 4:00 PM
Room: 500/1-001 - Main Auditorium Nonintegrable QFTs are expected to thermalize and exhibit emergence of hydrodynamics and chaos. In weakly coupled QFTs, kinetic theory captures local thermalization; such a versatile tool is absent away from the perturbative regime. I will present analytical and numerical results using nonperturbative methods to study thermalization at strong coupling. I will show how requiring causality in the thermal state leads to strong analytic constraints on the thermodynamics and out of equilibrium properties of any relativistic 1+1d QFT. I will then discuss Lightcone Conformal Truncation (LCT) as a powerful numerical tool to study thermalization of QFTs. Applied to $\phi^4$ theory in 1+1d, LCT reveals eigenstate thermalization and onset of random matrix universality at any nonzero coupling. Finally, I will discuss prospects for observing the emergence of hydrodynamics in QFTs using Hamiltonian truncation.
4:00 PM Coffee Break
Coffee Break
4:00 PM - 4:30 PM

4:30 PM Structured Discussion
Structured Discussion
4:30 PM - 6:00 PM
Room: 500/1-001 - Main Auditorium
Friday, May 27, 2022

9:30 AM Coffee Break
Coffee Break
9:30 AM - 10:00 AM
10:00 AM Post-Quantum Quench Growth of Renyi Entropies in Perturbed Luttinger Liquids - Robert Konik (Brookhaven National Laboratory)
Post-Quantum Quench Growth of Renyi Entropies in Perturbed Luttinger Liquids
- Robert Konik (Brookhaven National Laboratory)
10:00 AM - 11:00 AM
Room: 500/1-001 - Main Auditorium The growth of Renyi entropies after the injection of energy into a correlated system provides a window upon the dynamics of its entanglement properties. We provide here a scheme by which this growth can be determined in Luttinger liquids systems with arbitrary interactions, even those introducing gaps into the liquid. This scheme introduces the notion of a generalized mixed state Renyi entropy. We show that these generalized Renyi entropies can be computed and provide analytic expressions thereof. Using these generalized Renyi entropies, we provide analytic expressions for the short time growth of the second and third Renyi entropy after a quantum quench of the coupling strength between two Luttinger liquids, relevant for the study of the dynamics of cold atomic systems. For longer times, we use truncated spectrum methods to evaluate the post-quench Renyi entropy growth.
12:00 PM Lunch
Lunch
12:00 PM - 2:00 PM
2:00 PM Multi-particle observables from a finite Euclidean spacetime* - Maxwell Hansen (University of Edinburgh)
Multi-particle observables from a finite Euclidean spacetime*
- Maxwell Hansen (University of Edinburgh)
2:00 PM - 3:00 PM
Room: 500/1-001 - Main Auditorium Numerical calculations using lattice-regularized QFTs are a powerful tool to understand nonperturbative systems when analytic methods are unavailable. However, the utility of numerical results can be affected by two issues: (i) calculations are necessarily performed in a finite-volume spacetime and (ii) Euclidean- (rather than Minkowski-) signature correlation functions are evaluated. Both aspects play an especially important role for multi-particle observables including scattering and decay amplitudes and inclusive rates. In this talk, I will discuss progress in extracting such observables from numerical lattice field theory, based on two strategies. One is to use the finite-volume as a tool, rather than an unwanted artefact, and to apply generic field theoretic relations between finite-volume quantities and infinite-volume amplitudes. The second is to carefully regulate the inverse Laplace transform, in order to estimate Minkowski observables directly from numerical Euclidean correlators.
3:30 PM Coffee Break
Coffee Break
3:30 PM - 4:00 PM
Saturday, May 28, 2022
Sunday, May 29, 2022

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