Triangle Seminars
Monday, 15 Mar 2021
Lonti: Entanglement in 1+1D Quantum Field Theory
Olalla Castro Alvaredo
(City)
Abstract:
This tutorial is available via youtube at https://youtu.be/zU-BRF6xLik. In this short course I will introduce branch point twist fields and explain how they emerge in the context of computing entanglement measures in 1+1D.
I will focus on massive 1+1D integrable quantum field theory (IQFT) and also comment on some well-known results in conformal field theory (CFT).
The talk will be structured into three main parts:
First, I will introduce entanglement measures, focussing on the entanglement entropy, explain how these measures relate to partition functions in multi-sheeted Riemann surfaces and how these, in turn, may be expressed as correlators of branch point twist fields.
Second, I will show how several well-known results in CFT and IQFT are very easily derived in this branch point twist field picture and how they can also be recovered numerically in a quantum spin chain.
Finally, I will explain how more involved computations with branch point twist fields may be performed by exploiting form factor technology and will end the talk by showing an example of one such calculation.
This tutorial is available via youtube at https://youtu.be/zU-BRF6xLik. In this short course I will introduce branch point twist fields and explain how they emerge in the context of computing entanglement measures in 1+1D.
I will focus on massive 1+1D integrable quantum field theory (IQFT) and also comment on some well-known results in conformal field theory (CFT).
The talk will be structured into three main parts:
First, I will introduce entanglement measures, focussing on the entanglement entropy, explain how these measures relate to partition functions in multi-sheeted Riemann surfaces and how these, in turn, may be expressed as correlators of branch point twist fields.
Second, I will show how several well-known results in CFT and IQFT are very easily derived in this branch point twist field picture and how they can also be recovered numerically in a quantum spin chain.
Finally, I will explain how more involved computations with branch point twist fields may be performed by exploiting form factor technology and will end the talk by showing an example of one such calculation.
Posted by: pethybridge
Lonti: Gravity and black holes in AdS
Toby Wiseman
(IC)
Abstract:
This is the live session included as part of the LonTI lecture on Gravity and black holes in AdS. Please register at https://lonti.weebly.com/registration.html to receive joining instructions for this live session which will be held via Zoom.Gravity in asymptotic AdS spacetimes behaves in many ways quite differently to the usual asymptotically flat situation we are usually introduced to. It is very important in understanding the AdS-CFT correspondence, and many of these differences to the flat setting have important implications. In this lecture and the problem sheet I will introduce AdS spacetime, asymptotic AdS spacetimes and then focus on the physics of black holes in AdS. For the simplest static black holes we will explore their behaviour, the implications for AdS-CFT and introduce some basic calculational tools to study them.
This is the live session included as part of the LonTI lecture on Gravity and black holes in AdS. Please register at https://lonti.weebly.com/registration.html to receive joining instructions for this live session which will be held via Zoom.Gravity in asymptotic AdS spacetimes behaves in many ways quite differently to the usual asymptotically flat situation we are usually introduced to. It is very important in understanding the AdS-CFT correspondence, and many of these differences to the flat setting have important implications. In this lecture and the problem sheet I will introduce AdS spacetime, asymptotic AdS spacetimes and then focus on the physics of black holes in AdS. For the simplest static black holes we will explore their behaviour, the implications for AdS-CFT and introduce some basic calculational tools to study them.
Posted by: pethybridge
Tuesday, 16 Mar 2021
Encoding the hologram into matrices
Masanori Hanada
( University of Surrey)
Abstract:
In holography, the geometry of gravitational theory should be encoded in its non-gravitational dual. In particular, in gauge/gravity duality, the geometry should be encoded into the color degrees of freedom (matrices) in U(N) supersymmetric Yang-Mills theory.
When the Yang-Mills theory is regarded as the low-energy effective theory of a system of N D-branes and open strings between them. Transverse spatial directions emerge from scalar fields, which are N*N matrices with color indices; roughly speaking, the eigenvalues are the locations of D-branes. In the past, it was argued that this simple 'emergent space' picture cannot be used in the context of gauge/gravity duality, because the ground-state wave function delocalizes at large N, leading to a conflict with the locality in the bulk geometry.
We show that this conventional wisdom is not correct: the ground-state wave function does not delocalize, and there is no conflict with the locality of the bulk geometry. This conclusion is obtained by clarifying the meaning of the 'diagonalization of a matrix' in Yang-Mills theory, which is not as obvious as one might think. This observation opens up the prospect of characterizing the bulk geometry via the color degrees of freedom in Yang-Mills theory, all the way down to the center of the bulk.
[please email a.held@imperial.ac.uk for zoom link or password]
In holography, the geometry of gravitational theory should be encoded in its non-gravitational dual. In particular, in gauge/gravity duality, the geometry should be encoded into the color degrees of freedom (matrices) in U(N) supersymmetric Yang-Mills theory.
When the Yang-Mills theory is regarded as the low-energy effective theory of a system of N D-branes and open strings between them. Transverse spatial directions emerge from scalar fields, which are N*N matrices with color indices; roughly speaking, the eigenvalues are the locations of D-branes. In the past, it was argued that this simple 'emergent space' picture cannot be used in the context of gauge/gravity duality, because the ground-state wave function delocalizes at large N, leading to a conflict with the locality in the bulk geometry.
We show that this conventional wisdom is not correct: the ground-state wave function does not delocalize, and there is no conflict with the locality of the bulk geometry. This conclusion is obtained by clarifying the meaning of the 'diagonalization of a matrix' in Yang-Mills theory, which is not as obvious as one might think. This observation opens up the prospect of characterizing the bulk geometry via the color degrees of freedom in Yang-Mills theory, all the way down to the center of the bulk.
[please email a.held@imperial.ac.uk for zoom link or password]
Posted by: IC
Wednesday, 17 Mar 2021
D-instanton amplitude in string theory
Ashoke Sen
(HCRI)
Abstract:
D-instantons give non-perturbative contribution to string theory amplitudes which can be computed using world-sheet techniques. However the integrals that appear in this computation often have divergences from corners of the moduli spaces which cannot be tamed by the usual procedure of analytic continuation. We show how using insights from string field theory we can extract finite unambiguous results from these apparently divergent integrals.
The Zoom link will be sent by your local Triangle seminar organiser or you can contact bogdan.stefanski.1@city.ac.uk
D-instantons give non-perturbative contribution to string theory amplitudes which can be computed using world-sheet techniques. However the integrals that appear in this computation often have divergences from corners of the moduli spaces which cannot be tamed by the usual procedure of analytic continuation. We show how using insights from string field theory we can extract finite unambiguous results from these apparently divergent integrals.
The Zoom link will be sent by your local Triangle seminar organiser or you can contact bogdan.stefanski.1@city.ac.uk
Posted by: CityU2
Thursday, 18 Mar 2021
TTbar-deformed conformal field theories out of equilibrium
Takato Yoshimura
(Tokyo Institute of Technology)
Abstract:
In this talk I will discuss the universal properties of transport phenomena in TTbar-deformed conformal field theories. TTbar-deformed CFTs are exactly solvable and admit a number of approaches, each of which is seemingly unrelated. Amongst them, for our purpose, which is to study transport phenomena in TTbar-deformed CFTs, we make use of the following: integrability and holography. I will apply these two approaches to study non-equilibrium steady states and Drude weights, finding perfect agreement. I will also discuss a curious connection between TTbar-deformed CFTs and an integrable cellular automaton model called the Rule 54 chain. –––- Part of the London Integrability Journal Club. If you are a new participant, please register at integrability-london.weebly.com. The link will be emailed.
In this talk I will discuss the universal properties of transport phenomena in TTbar-deformed conformal field theories. TTbar-deformed CFTs are exactly solvable and admit a number of approaches, each of which is seemingly unrelated. Amongst them, for our purpose, which is to study transport phenomena in TTbar-deformed CFTs, we make use of the following: integrability and holography. I will apply these two approaches to study non-equilibrium steady states and Drude weights, finding perfect agreement. I will also discuss a curious connection between TTbar-deformed CFTs and an integrable cellular automaton model called the Rule 54 chain. –––- Part of the London Integrability Journal Club. If you are a new participant, please register at integrability-london.weebly.com. The link will be emailed.
Posted by: andrea