Takahisa Igata, KEK
[Cosmophys seminar] Photon escape probability from the vicinity of a Kerr black hole
Online (Zoom)
With the recent development of black hole shadow observations, phenomena in the vicinity of an event horizon have become a subject of observations. In this seminar, we will focus on a light source in the vicinity of a Kerr black hole and consider an escape probability and frequency shift of photons emitted from the source to infinity. We also discuss how the proper motion of the source affects these observational indices.
Denny Lane B. Sombillo, Osaka University
Application of deep learning to the study of near-threshold resonances
Online (Zoom), indico page, slides (kek.jp only)
Peak structures in the scattering experiments are often interpreted as a manifestation of a resonance state. A more rigorous approach requires that we associate at least one S-matrix pole to the peak structure to qualify as a physical state. The presence of a nearby threshold complicates the situation. Sometimes, near-threshold virtual and quasi-bound states produce a similar peak structure. In our work, we phrased the problem as a classification task and solved them using deep learning. In the first part of this talk, I will discuss how deep learning is applied to distinguish virtual and bound state enhancements in the single-channel nucleon-nucleon system. Even without appealing to deuteron’s existence, our deep neural network models can distinguish the two enhancements. In the last part, I will discuss how this approach can be extended to the coupled-channel problem. Specifically, we designed a deep neural network that can extract the coupled-channel S-matrix pole configuration. The resulting training dataset requires a nonconventional training loop; otherwise, the deep neural network will not learn. Finally, we apply our model to the study of the pion-nucleon scattering near the eta-nucleon threshold. I will also discuss some preliminary results.
Toyokazu Sekiguchi, KEK
[Cosmophys seminar] Revisiting constraints on dark matter annihilation from global 21cm signals
Online(Zoom)
When dark matter annihilation takes place in the Universe at high redshifts (between recombination and reionization), energetic particles are injected into intergalactic medium (IGM), which is filled with neutral hydrogen. By ionizing and heating IGM, dark matter annihilation can affect redshifted 21cm signals, which EDGES have claimed to detect for the first time. After reviewing how redshifted 21cm signals are modified by dark matter annihilation, we revisit the constraints based on the EDGES result. In particular, we’ve performed dedicated N-body simulations in order to estimate dark matter clumpiness, as known as boost factor, which has results in constraints more conservative than previously estimated.
Kazuki Enomoto, Osaka University
Higher dimensional LNV operators and their renormalization
Online (Zoom), indico page, slides (kek.jp only)
Although the Standard Model (SM) is a successful theory, some mysterious phenomena such as tiny neutrino masses are observed. We need physics beyond the SM to explain these phenomena. Observed tiny neutrino masses would indicate the lepton number violation (LNV) in new physics. If the scale of LNV is much higher than the electroweak scale, low-energy physics is described by the effective field theory with higher dimensional LNV operators. Therefore, the higher dimensional LNV operator is one of the important clues to search for new physics. In this seminar, I will talk about our two studies about LNV operators. One is about the operator between a same-sign lepton pair and a pair of W bosons, which is generated from d=7 and 9 LNV operators. We studied how to test this operator by using data of neutrino oscillation, neutrinoless double beta decay, muon-positron conversion, and future high-energy colliders. The other is about the renormalization of higher dimensional LNV operators. Some higher dimensional LNV operators generate Majorana neutrino masses via divergent loop diagrams, and the renormalization is needed for model-independent analyses. We investigated d=5 and 7 LNV operators and Majorana neutrino masses at one-loop level, and we found that divergence at one-loop level can be renormalized by using counter term from higher dimensional operators. The former topic is based on Phys. Rev. D101, 115019 (arXiv:2002.12265), and the latter is based on the work in progress.
Yu Zhang, Central China Normal University
Revisiting Correlated Dirac eigenvalues and axial anomaly in chiral symmetric QCD
Online (Zoom), indico page, slides (kek.jp only)
How axial anomaly manifests itself at the chiral phase transition temperature affects the nature of chiral phase transition and it is a fundamental question in QCD. We performed a first continuum and chiral extrapolation of two UA(1)UA(1) measures in (2+1)-flavor lattice QCD at T=205T=205 MeV. By using the proposed novel relations between the quark mass derivatives of Dirac eigenvalue spectrum ρρ and correlation functions among eigenvalues we find that the microscopic origin of the current manifested axial anomaly is the peak structure developed in ρρ with its height proportional to quark mass squared. These strongly suggest the chiral phase transition belongs to 3-d O(4) universality class.
Csaba Csaki, Cornell University
Magnetic scattering: pairwise little group and pairwise helicity
Online (Zoom) https://kds.kek.jp/event/36580/
I discuss how to construct a Lorentz-invariant S-matrix for the scattering of electrically and magnetically charged particles. A key ingredient is a revision of our fundamental understanding of multi-particle representations of the Poincare group. Surprisingly, the asymptotic states for electric-magnetic scattering transform with an additional little group phase, associated with pairs of electrically and magnetically charged particles. I will discuss the general construction of such states. The resulting “pairwise helicity” is identified with the quantized “cross product” of charges e1 g2- e2 g1 for every charge-monopole pair, and represents the extra angular momentum stored in the asymptotic electromagnetic field. We define a new kind of pairwise spinor-helicity variable, which serves as an additional building block for electric-magnetic scattering amplitudes. We then construct the most general 3-point S-matrix elements, as well as the full partial wave decomposition for the 2 -> 2 fermion-monopole S-matrix. In particular, we derive the famous helicity flip in the lowest partial wave as a simple consequence of a generalized spin-helicity selection rule, as well as the full angular dependence for the higher partial waves. Our construction provides a significant new achievement for the on-shell program, succeeding where the Lagrangian description has so far failed.
Shoji Hashimoto, KEK
[EX] What is quark-hadron duality and how to overcome?
Online (Zoom) https://kds.kek.jp/event/36347/
Quark-hadron duality refers to an assumption that one can use perturbative QCD to compute a class of physical processes. Its associated uncertainty is hard to quantify, and even ignored in some cases, which may pose significant problem on the analysis of precise experimental data. We develop a formalism to get rid of this assumption and compute the physical processes fully non-perturbatively using lattice QCD. Examples are inclusive semileptonic decays of B meson and lepton-nucleon inelastic scattering cross section at low energy.
Sayantan Sharma, Institute of Mathematical Sciences
[QCD theory Seminar] Updates on Chiral plasma instabilities in gauge theory from lattice
Online (Zoom)
In this talk I will discuss about the latest understanding on chiral plasma instabilities and the onset of chiral turbulence in Abelian plasmas far from equilibrium. By performing classical lattice simulations of the microscopic theory, we show that the generation of strong helical magnetic fields from a helicity imbalance in the fermion sector proceeds through three distinct steps. During the initial stages the helicity imbalance of the fermion sector causes an exponential growth of magnetic field modes with right handed polarization. Secondary growth of unstable modes accelerates the helicity transfer from fermions to gauge fields and ultimately leads to the emergence of a self-similar scaling regime characteristic of decaying turbulence, where magnetic helicity is efficiently transferred to macroscopic length scales. In the turbulent regime the evolution of magnetic helicity spectrum can be described by an infrared power-spectrum with spectral exponent $¥kappa = 10.2¥pm 0.5$, which we determine from our simulations. I will conclude by discussing some expectations about this phenomenon in non-Abelian gauge theories.
Yutaka Matsuo, Tokyo University
Dimensional oxidization on coset space
Online (Zoom), indico page, slides (kek.jp only) In the matrix model approaches of string/M theories, one starts from a generic symmetry gl(infty) to reproduce the space-time manifold.
In the matrix model approaches of string/M theories, one starts from a generic symmetry gl(infty) to reproduce the space-time manifold.
In this talk, we propose the generalization in which the space-time manifold emerges from a gauge symmetry algebra which is not necessarily gl(infty).
We focus on the second nontrivial example after the toroidal compactification, the coset space G/H, and propose a specific infinite- dimensional symmetry which realizes the geometry.
It consists of the gauge-algebra valued functions on the coset and Lorentzian generator pairs associated with the isometry.
We show that the 0-dimensional gauge theory with the mass and Chern- Simons terms gives the gauge theory on the coset with scalar fields associated with H.
宮下精二, 日本物理学会, 東大物性研
[KEK連携コロキウム] 磁石への微視的モデルからのアプローチ −有限温度での保磁力解析−
Online (Zoom)
