セミナー 2021年

Kazuhiro Tanaka, Juntendo University

Operator relations for the GPDs and the gravitational form factors of hadrons

Online (Zoom)
The gravitational form factors for a hadron, the form factors for the hadron matrix element of the QCD energy-momentum tensor, not only describe the coupling of the hadron with a graviton, but also serve as unique quantities for describing the shape inside the hadron reflecting dynamics of quarks and gluons, such as the internal shear forces acting on the quarks/gluons and their pressure distributions. The gravitational form factors are also relevant to understanding the origin of the nucleon mass and the origin of the nucleon spin, which are the important objectives at J-PARC. We consider the quark/gluon contributions to the gravitational form factors for a hadron, in particular, for a (pseudo)scalar hadron and for the nucleon. We derive and clarify the relations satisfied by the gravitational form factors as direct consequences of the symmetries and the equations of motion in QCD, and connections to the generalized parton distributions (GPDs). Our results reveal the connections between the gravitational form factors and the higher-twist quark-gluon correlation effects inside the hadrons. Furthermore, we are able to constrain the twist-four gravitational form factors by the trace anomalies in QCD, and derive the corresponding relations at the three-loop level.

Yusuke Yamada, RESCEU, University of Tokyo

Aether supersymmetry breaking

Online (Zoom) https://kds.kek.jp/event/40348/
Supersymmetry breaking mechanism plays one of the most important roles for constructing realistic models within supersymmetric theory. Either F-term or D-term breaking scenarios have been studied in most phenomenological models. What else is available? In this talk, I will discuss a new possibility, which I call aether SUSY breaking, where some part of Poincare symmetry is also broken simultaneously. I will show a concrete model of the new scenario and discuss SUSY breaking mediation to matter sectors. It turns out that SUSY breaking can be mediated to matters in a very similar way to the gravity mediation in F-term models. I will also discuss cosmological constraints on the model, which gives the upper bound on the SUSY breaking scale (

Toshifumi Noumi, Kobe University

Gravitational Positivity Bounds and the Standard Model

Online (Zoom) https://kds.kek.jp/event/40423/
Positivity bounds on low-energy scattering amplitudes provide a criterion for a low-energy effective theory to have a standard UV completion. When applied to gravitational theories, they are expected to imply non-trivial quantum gravity constraints on quantum field theory models, i.e., swampland conditions. In this talk I will introduce recent developments on positivity bounds in gravitational theories and their implications for the Standard Model of particle physics.

Keisuke Harigaya, CERN

Cosmology of Axion Rotation

Online (Zoom) https://kds.kek.jp/event/40466/
We will introduce new cosmological dynamics of the QCD axion and axion-like particles, where the axion field rotates in field space. Axion dark matter may be produced from the kinetic energy of the axion and the required axion decay constant is much below the prediction of the conventional evolutions. The angular momentum of the rotation is transferred into baryon asymmetry through baryon number violating interactions. We discuss the electroweak sphaleron process, Majorana neutrino mass, and R-parity violation and predictions on the parameters of each theory. In some of the parameter space the rotation dominates the energy density of the universe. The resultant kination-dominated era modifies primordial gravitational wave spectra.

Igor Shovkovy, Arizona State University

[QCD theory Seminar] Chiral anomalous plasma in magnetospheres of pulsars

Online (Zoom)
I will discuss some general properties of the magnetospheres of pulsars and black holes. Their rich dynamics are responsible for many interesting phenomena, such as the powerful polar jets and fast radio bursts. The magnetospheres are made mainly of a force-free magnetized plasma, where the local electric field is perpendicular to the magnetic field. However, a consistent consideration of the dynamics points to the existence of transient gap regions in the magnetospheres where the projection of the electric field on the magnetic field must be nonzero. Under such conditions, the chiral anomaly can be activated and produce a nonzero chiral charge density in the plasma. In the case of supermassive black holes, the chiral charge is too small to have any observable effects. In contrast, the chiral asymmetry produced in the magnetospheres of magnetars can be substantial. It can trigger chiral plasma instability and possibly lead to observable phenomena in magnetars.

米谷 民明 名誉教授, 東京大学

[KEK連携コロキウム] 弦理論の意味 - 歴史からの展望

Online (Zoom)

Soeren Schlichting, Bielefeld University

[QCD theory Seminar] Dynamic critical behavior in the Z_2 Ising and O(4) universality classes

Online (Zoom)
In this talk I will discuss the dynamic critical behavior of relativistic scalar field theories, with dissipative (Model A), diffusive (Model B) and conservative (Model C/D) dynamics. Based on first principle simulations, I will discuss the manifestations of the critical behavior in real-time correlation functions and extract universal scaling functions that describe the spectral functions of the order parameter in the vicinity of the critical point. If time remains I will also present preliminary results for the evolution of cumulants of the order parameter in non-equilibrium phase transitions, where a system dynamically transits the critical point in the phase diagram.

Neill Warrington, University of Washington

Contour Deformations for Lattice Field Theory

Online(Zoom), slides (kek.jp only)
Highly oscillatory path integrals are common in lattice field theory.
They crop up as sign problems and as signal to noise problems and prevent Monte Carlo calculations of both lattice QCD at finite chemical potential and real-time dynamics. A general method for treating highly oscillatory path integrals has emerged in which the domain of integration of the path integral is deformed into a complexified field space. In this talk I will review this method, and I will discuss recent progress in machine learning manifolds for lattice QCD.

Masaru Hongo Affiliation, University of Illinois Chicago

[QCD theory Seminar] Relativistic spin hydrodynamics with torsion and linear response theory for spin relaxation

Online (Zoom)
Recent experimental observation of spin polarization of hadrons in relativistic heavy-ion collisions [1] motivates the development of the theory describing spin transport in relativistic plasma. In this talk, I will introduce our recent work on a theoretical formulation of relativistic spin hydrodynamics based on the second law of local thermodynamics and linear response theory [2]. We work in a regime where spin density, which is assumed to relax much slower than other non-hydrodynamic modes, is treated as an independent degree of freedom in an extended hydrodynamic description. Spin hydrodynamics in our approach contains only three non-hydrodynamic modes corresponding to a spin vector, whose relaxation time is controlled by a new transport coefficient, the rotational viscosity. Using the derived constitutive relation, I will explain our main results; an interesting mode mixing phenomenon between the transverse shear and the spin density modes, and several field-theoretical ways to compute the rotational viscosity via the Green-Kubo formula based on retarded correlation functions.

[1] STAR Collaboration, L. Adamczyk et al., Nature 548 (2017) 62?65, arXiv:1701.06657 [nucl-ex]
[2] M. Hongo, X-G. Huang, M. Kaminski, M. Stephanov, H-U Yee, arXiv:2107.14231 [hep-th]

Boram Yoon, LANL

Machine Learning Prediction and Compression of Lattice QCD Observables

Online (Zoom)
In lattice QCD simulations, a large number of observables are measured on each Monte Carlo sample of the QCD universe, called gauge configuration. Since the measured observables share the same background gauge configuration, their statistical fluctuations are correlated with each other, and analyzing such correlation is a well-suited problem for machine learning (ML) algorithms. In this talk, I will present two ML applications to lattice QCD problems: (1) prediction of unmeasured-but-computationally-expensive observables from the cheap observables on each gauge configuration, and (2) compression of lattice QCD data using D-Wave quantum annealer as an efficient binary optimization algorithm. For both applications, a bias correction algorithm is applied to estimate and correct the systematic error due to inexact ML predictions and reconstruction.

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