Kiyoharu Kawana, Seoul National University
Multi-critical point principle and its Phenomenology
Online (Zoom) https://kds.kek.jp/event/40651/
Multi-critical point principle (MPP) is an interesting theoretical possibility, which claims that coupling constants of low energy effective theory are tuned to the point where the vacuum structure or history of the Universe changes drastically. In this talk, I will try to explain the basic concepts and ideas of the MPP without going into the details of underlying physics. Then, I will present a few phenomenological applications of this principle, including our recent works (arXiv:2107.10720 and paper in preparation).
Yuuki Hayashi, Tohoku University
Renormalon subtraction using Fourier transform - towards precise QCD calculation
Online (Zoom)
Perturbative QCD gives divergent series due to renormalons, and theoretical predictions using such series are essentially ambiguous. By subtracting renormalons from the Wilson coefficients in the framework of the operator product expansion (OPE), we can achieve a precise calculation of the QCD effect. We propose a method for renormalon subtraction with systematic approximation accuracy by using the Fourier transform. It utilizes the properties of the Fourier transform, and the Wilson coefficient with the renormalons removed is presented as a one-parameter integral whose integrand has suppressed (or vanished) renormalons. In this talk, I will show an application to B and D meson masses as one of the first analyses. By subtracting the ambiguities of $O(¥Lambda_{QCD})$ and $O(¥Lambda_{QCD}^2/m)$, the non-perturbative parameters of HQET are determined with high accuracy. The results are consistent with theoretical expectations, and improvements in convergence and scale dependence are confirmed.
Raul Briceno, Old Dominion University
Long-range processes in QCD
Online (Zoom) A rich variety of phenomena in the Standard Model and its extensions manifest in long-range processes involving bound states of quantum chromodynamics (QCD), namely hadrons. These are processes where intermediate hadronic states propagate over a long distance, between electroweak interactions. Examples include virtual Compton scattering and double-beta decay. Such processes are at the cusp of what can be systematically studied given two challenges. First, these reactions involve hadrons, and as a result one must use a non-perturbative tool to access their amplitudes. Currently lattice QCD is the only systematically improvable way we have for doing just this. Second, lattice QCD is defined in a finite, Euclidean spacetime. This introduces its own specific challenges, time in purely imaginary in lattice QCD, and by truncating the space one looses the notion of asymptotic states.
A rich variety of phenomena in the Standard Model and its extensions manifest in long-range processes involving bound states of quantum chromodynamics (QCD), namely hadrons. These are processes where intermediate hadronic states propagate over a long distance, between electroweak interactions. Examples include virtual Compton scattering and double-beta decay. Such processes are at the cusp of what can be systematically studied given two challenges. First, these reactions involve hadrons, and as a result one must use a non-perturbative tool to access their amplitudes. Currently lattice QCD is the only systematically improvable way we have for doing just this. Second, lattice QCD is defined in a finite, Euclidean spacetime. This introduces its own specific challenges, time in purely imaginary in lattice QCD, and by truncating the space one looses the notion of asymptotic states.
In this talk I explain how these issues can all be resolved systematically for a relatively large kinematic region. In presenting the necessary formalism for doing this, I will summarize recent progress in lattice QCD in order to argue that the community is up to the challenge.
Massimo D'Elia, University of Pisa
[QCD Theory Seminar] Updates on the QCD Phase Diagram in a Magnetic Field
Online (Zoom)
I will review results regarding the QCD Phase Diagram in the presence of a magnetic background field, based on lattice QCD simulations. In particular, I will discuss recent numerical evidence that the thermal QCD crossover turns into a first order transition for large enough magnetic fields. The critical endpoint is found to be located between eB = 4 GeV^2 and 9 GeV^2, with the corresponding critical temperature ranging between 100 and 60 MeV.
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 (
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)
