セミナー 2020年

Kazuya Mameda, RIKEN

Chiral transport under gravitational field

Online (Zoom), slides (kek.jp only)
The kinetic theory is a fundamental tool to describe transport phenomena, such as that induced by quantum anomaly. In this talk, we explain how the Boltzmann transport theory is modified by quantum corrections. Also we show the field-theoretical derivation of the kinetic theory of chiral fermions in general curved spacetime. Then, we briefly discuss possible applications of the resulting framework to high-energy and condensed matter physics.

Hua Xing Zhu, Zhejiang University

[QCD theory Seminar]Double-slit interference in jet substructure and light-ray OPE

Online (Zoom)
The flow of energy within jets is characterized by correlation functions of energy flow operators, with the three-point correlator, being the first correlator with non-trivial shape dependence, playing a special role in unravelling the dynamics of QCD. In this talk we consider the three-point energy correlator to all orders in the strong coupling constant, in the limit where two of the detectors are squeezed together. We show that by rotating the two squeezed detectors with respect to the third by an angle ¥phi?, a ¥cos (2¥phi)cos(2?) dependence arising from the quantum interference between intermediate virtual gluons with +/-+/? helicity is imprinted on the detector. This can be regarded as a double-slit experiment performed with jet substructure, and it provides a direct probe of the ultimately quantum nature of the substructure of jets, and of transverse spin physics in QCD. To facilitate our all-orders analysis, we adopt the Operator Product Expansion (OPE) for light-ray operators in conformal field theory and develop it in QCD. Our application of the light-ray OPE in real world QCD establishes it as a powerful theoretical tool with broad applications for the study of jet substructure.

Kazunori Kohri, KEK

[EX] Higgs vacuum metastability in primordial inflation

Online (Zoom) https://kds.kek.jp/event/36167/
Current measurements of the Higgs boson mass and top Yukawa coupling suggest that the effective Higgs potential develops an instability below the Planck scale. If the energy scale of inflation in the early Universe is as high as the GUT scale, inflationary quantum fluctuations of the Higgs field can easily destabilize the standard electroweak vacuum. This instability produces dangerous AdS domains which should have swallowed the whole Universe.
Notice: In the seminar, there will be a mini lecture by Prof. Ryuichiro Kitano (KEK theory center) on the renormalization of the Higgs potential prior to Kohri-san’s talk.

Shi Pu, USTC

[QCD theory Seminar] Spin Hydrodynamics and Symmetric Energy-Momentum Tensors

Online (Zoom)
We discuss a puzzle in relativistic spin hydrodynamics; in the previous formulation the spin source from the antisymmetric part of the canonical energy-momentum tensor (EMT) is crucial. The Belinfante improved EMT is pseudo-gauge transformed from the canonical EMT and is usually a physically sensible choice especially when gauge fields are coupled as in magnetohydrodynamics, but the Belinfante EMT has no antisymmetric part. We find that pseudo-transformed entropy currents are physically inequivalent in nonequilibrium situations. We also identify a current induced by the spin vorticity read from the Belinfante symmetric EMT.

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.
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 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.

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