Takuya Okuda, Tokyo University
U(1) spin Chern-Simons theory and Arf invariants in two dimensions
Online (Zoom) https://kds.kek.jp/event/36168/
The level-k U(1) Chern-Simons theory with k odd is an example of spin topological quantum field theory (spin TQFT), i.e., a TQFT whose partition functions and states depend on the spin structure of spacetime. Its dynamics is expected to be captured by the 2d CFT of a free compact boson with a certain radius. Recently it was recognized that an appropriate dependence on the 2d spin structure can be given to the CFT by modifying the theory using the so-called Arf invariant. We demonstrate that one can reorganize the torus partition function of the modified CFT into a sum involving a finite number of conformal blocks. This allows us to reproduce the modular matrices of the spin theory. We use the modular matrices to calculate the partition function of the spin Chern-Simons theory on the lens space, and demonstrate the expected dependence on the 3d spin structure. As an introduction to the topic the talk will include an elementary review of the topological phase of matter.
Arata Yamamoto, Tokyo University
Real-time simulation of Z2 lattice gauge theory on qubits
Online (Zoom), indico page, slides (kek.jp only) In this seminar, I talk about the quantum simulation of Z2 lattice gauge theory in 2+1 dimensions. I discuss the real-time evolution of the system with two static charges, i.e., two Wilson lines.
In this seminar, I talk about the quantum simulation of Z2 lattice gauge theory in 2+1 dimensions. I discuss the real-time evolution of the system with two static charges, i.e., two Wilson lines.
The presentation is based on arXiv:2008.11395.
Kazumi Okuyama, Shinshu University
JT gravity and KdV equations
Online (Zoom), indico page, slides (kek.jp only) We study the thermal partition function of Jackiw-Teitelboim (JT) gravity using the matrix model description recently found by Saad, Shenker and Stanford. We show that the partition function of JT gravity is written as the expectation value of a macroscopic loop operator in the old matrix model of 2d gravity in the background where infinitely many couplings are turned on in a specific way. Based on this expression we develop a very efficient method of computing the partition function in the genus expansion as well as in the low temperature expansion by making use of the Korteweg-de Vries constraints obeyed by the partition function.
We study the thermal partition function of Jackiw-Teitelboim (JT) gravity using the matrix model description recently found by Saad, Shenker and Stanford. We show that the partition function of JT gravity is written as the expectation value of a macroscopic loop operator in the old matrix model of 2d gravity in the background where infinitely many couplings are turned on in a specific way. Based on this expression we develop a very efficient method of computing the partition function in the genus expansion as well as in the low temperature expansion by making use of the Korteweg-de Vries constraints obeyed by the partition function.
We also generalize our analysis to the case of multi-boundary correlators with the help of the boundary creation operator. We formulate a method of computing it up to any order and also find a universal form of the two-boundary correlator in terms of the error function. Using this result we are able to write down the analytic form of the spectral form factor in JT gravity and show how the ramp and plateau behavior arises.
This talk is based on the work with Kazuhiro Sakai (arXiv:1911.01659,arXiv:2004.07555).
Kai Schmitz, CERN
Has NANOGrav found first evidence for cosmic strings?
Online (Zoom), indico page, slides (kek.jp only)
The NANOGrav pulsar timing collaboration has recently reported strong evidence for a new stochastic common-spectrum process affecting the pulsar timing residuals in its 12.5-year data set. If confirmed in the future, this signal may turn out to be the first glimpse of a stochastic gravitational-wave background at nanohertz frequencies. In the first half of this talk, I will review the NANOGrav experiment, discuss the properties of the observed signal, and comment on its astrophysical interpretation in terms of inspiraling supermassive black-hole binaries. In the second half of the talk, I will then turn to possible explanations based on physics beyond the standard model, in particular, the possibility of gravitational waves emitted by a network of cosmic strings. In this case, the NANOGRAV signal may be a first peek at the dynamics of the early Universe at energies close to the scale of grand unification. This talk is based on 2009.06607 and 2009.10649.
Takahiro Miura, Osaka University
[QCD theory Seminar] Quantum Dissipation of Quarkonium in Quark Gluon Plasma
Online (Zoom)
The properties of quark gluon plasma (QGP) have been investigated in heavy ion collision experiments. There, the suppression of quarkonium yield is regarded as a good probe for the screening of color charges in the QGP. Since the experimental data of quarkonium reflect its entire evolution in the QGP, it is important to develop our understanding of the in-medium evolution of quarkonium. We discuss the dynamics of quarkonium by applying the methods of open quantum systems. In this framework, information of the system is given by a density matrix, whose evolution is described by the master equation. Recently the effects of quantum dissipation on the dynamics have been discussed and its importance has been shown [1,2]. In this talk, we derive the master equation in the Lindblad form for the relative motion of a quarkonium. We solve the Lindblad equation by quantum state diffusion method and discuss how the dissipation and the color singlet-octet transitions affect quarkonium equilibration process. [1] Akamatsu et.al, Quantum dissipation of a heavy quark from a nonlinear stochastic Schrodinger equation,arXiv:1805.00167,JHEP07(2018)029 [2] Miura et.al, Quantum Brownian motion of a heavy quark pair in the quark-gluon plasma,arXiv:1908.06293,Phys. Rev. D 101, 034011
Yosuke Imamura, Tokyo Institute of Technology
The superconformal index from the AdS/CFT correspondence
Online (Zoom), indico page, slides (kek.jp only)
The superconformal index (SCI) I(q) of a superconformal field theory (SCFT) is a series of q whose coefficients have information of the operator spectrum of the SCFT. Although there is a formula to calculate the SCI exactly for Lagrangian theories, we need to rely on some non-perturbative methods, like dualities, to obtain the SCI of non-Lagrangian theories. In this talk we discuss calculation of SCI with the AdS/CFT correspondence. It is commonly believed that for finite N field theories it is practically impossible to perform exact calculation on the AdS side due to quantum gravity corrections. I will point out that this is not the case for the SCI and propose a new method to calculate the exact SCI on the AdS side. As an application I calculate the SCI of S-fold theories, which are examples of non-Lagrangian SCFTs.
Toyohiro Tsurumaru, Mitsubishi Electric
[Quantum-Physics Seminar] Leftover hashing from quantum error correction: Unifying the two approaches to the security proof of quantum key distribution (in Japanese)
Seminar room, Kenkyu honkan 3F We show that the Mayers-Shor-Preskill approach and Renner’s approach to proving the security of quantum key distribution (QKD) are essentially the same. We begin our analysis by considering a special case of QKD called privacy amplification (PA). PA itself is an important building block of cryptography, both classical and quantum. The standard theoretical tool used for its security proof is called the leftover hashing lemma (LHL). We present a direct connection between the LHL and the coding theorem of a certain quantum error correction code. Then we apply this result to proving the equivalence between the two approaches to proving the security of QKD.
We show that the Mayers-Shor-Preskill approach and Renner’s approach to proving the security of quantum key distribution (QKD) are essentially the same. We begin our analysis by considering a special case of QKD called privacy amplification (PA). PA itself is an important building block of cryptography, both classical and quantum. The standard theoretical tool used for its security proof is called the leftover hashing lemma (LHL). We present a direct connection between the LHL and the coding theorem of a certain quantum error correction code. Then we apply this result to proving the equivalence between the two approaches to proving the security of QKD.
(References)
T. Tsurumaru, “Leftover Hashing From Quantum Error Correction: Unifying the Two Approaches to the Security Proof of Quantum Key Distribution”, in IEEE Transactions on Information Theory, vol. 66, no. 6, pp. 3465-3484, June 2020, (arXiv:1809.05479).
Toru Kojo, Central China Normal University
[QCD theory seminar] Hard- and Soft- Deconfinement from nuclear to quark matter
Online (Zoom) We propose a novel concept of hard and soft realizations of deconfinement from nuclear to quark matter. Hard Deconfinement takes place when bulk thermodynamics is dominated by the core properties. The energy density and mechanical pressure in a nucleon, which are related to the gravitational form factor in scattering experiments, are found to be consistent with high density constraints known from neutron star phenomenology. Meanwhile Soft Deconfinement is driven by quark exchanges at intermediate distance and begins before Hard Deconfinement happens. To describe this phenomenon we use a model of quantum percolation, and discuss a quantum mechanical problem of quarks hopping among baryons. We describe delocalization of quark wavefunctions as well as the Anderson localization.
We propose a novel concept of hard and soft realizations of deconfinement from nuclear to quark matter. Hard Deconfinement takes place when bulk thermodynamics is dominated by the core properties. The energy density and mechanical pressure in a nucleon, which are related to the gravitational form factor in scattering experiments, are found to be consistent with high density constraints known from neutron star phenomenology. Meanwhile Soft Deconfinement is driven by quark exchanges at intermediate distance and begins before Hard Deconfinement happens. To describe this phenomenon we use a model of quantum percolation, and discuss a quantum mechanical problem of quarks hopping among baryons. We describe delocalization of quark wavefunctions as well as the Anderson localization.
Finally we discuss how the quark Fermi sea is developed as nuclear matter transforms into quark matter, and conjecture a scenario leading to a momentum shell model in Quarkyonic Matter.
Yuichiro Tada, Nagoya University
Manifestly covariant theory of stochastic inflation
Online (Zoom) https://kds.kek.jp/event/35914/
The stochastic approach to inflation can non-perturbatively treat the superhorizon fluctuations as the classical random noise to go beyond the standard perturbative QFT approach. I first review how this approach enables us to calculate the observable curvature perturbations in a non-perturbative way and how it can be implemented in a numerical program. I then describe the covariance of the stochastic theory and the discretization scheme of the stochastic noise, which are important both theoretically and practically. Mathematically the stochastic noise can be discretized in an arbitrary manner, but we reveal the physically motivated discretization, which ensures the covariance of the stochastic theory on the inflatons’ target manifold.
Koji Hashimoto, Department of Physics, Osaka University
Building bulk from Wilson loops
Online (Zoom), indico page, slides (kek.jp only)
