2022年度のセミナー

Date/Place January 31th (Tue.) 15:40-16:40 / Hybrid (H701 + Online)
Name Kazuki Sakurai (Warsaw U.)
　Title　 Quantum information and CP measurement in H->tau,tau at future lepton colliders
Abstract It has been know that Quantum Mechanics allows a strong and bizarre correlation among particles, called entanglement, that is not possible in any alternative theories that are local and real. In those local-real theories, correlations among particles must satisfy Bell inequalities, while Quantum Mechanics can violate them. The entanglement and Bell inequalities are therefore thought of the key to understand Quantum Mechanics in a deeper level and play an important role in quantum information and computation theories. Violation of Bell inequalities has been observed in low energy experiments but it has not been tested at high-energy collider experiments with energy higher or around the weak scale. In this talk I will propose a collider measurement of various quantum properties in H->tau,tau at future lepton colliders and discuss its possible application to the CP measurements.

Date/Place January 24th (Tue.) 15:40-16:40 / Hybrid (H701 + Online)
Name Ryo Yokokura (KEK)
　Title　 Unstable Nambu-Goldstone modes
Abstract Nambu-Goldstone (NG) modes for 0-form and higher-form symmetries can become unstable in the presence of background fields. Examples include the instability of a photon with a time-dependent axion background or with a chirality imbalance, known as the chiral plasma instability, and the instability of a dynamical axion with a background electric field. We show that all these phenomena can be universally described by a symmetry algebra for 0-form and higher-form symmetries. We prove a counting rule for the number of unstable NG modes in terms of correlation functions of broken symmetry generators. Based on our unified description, we further give a simple new example where one of the NG modes associated with the spontaneous 0-form symmetry breaking $U(1) \times U(1) \to \{1\}$ becomes unstable.

Date/Place January 17th (Tue.) 15:40-16:40 / Hybrid (H701 + Online)
Name Michiru Niibo (Ochanomizu U.)
　Title　 Future Constraints on Neutrino Lines from Dark Matter
Abstract Neutrinos are the least constrained and are expected to shed new light on the state of dark matter detection. In particular, neutrino line spectra from MeV dark matter in our Galaxy are an important signal because they are detected in the inverse decay channel with little smearing effect. In this talk, I will discuss the possibility that JUNO, a future neutrino detector, will be able to detect neutrino lines from the annihilation and decay of MeV dark matter in a model-independent way. In addition, constraints from future neutrino detectors on a particular dark matter model motivated by a neutrino mass mechanism called the Majoron will be presented.

Date/Place January 10th (Tue.) 15:40-16:40 / Online (H701 + Public viewing)
Name Kazuya Yonekura (Tohoku U.)
　Title　 Cosmic strings from pure Yang-Mills theory
Abstract I review some properties of pure Yang-Mills theories and explain why color flux tubes can be cosmic strings. Their stability is explained by 1-form center symmetries.Their production in the thermal phase transition is explained by the qualitative picture coming from the electric-magnetic duality. Some of their further properties such as intercommutation probability in the large N limit can be understood by the theory of large N counting and holographic duality. Pure Yang-Mills theories are the simplest and natural models for cosmic strings, and may be observed by future gravitational wave experiments.

Date/Place December 20th (Tue.) 15:40-16:40 / Hybrid (H701 + Online)
Name Sotaro Sugishita (Nagoya U.)
　Title　 Rindler bulk reconstruction and subregion duality in AdS/CFT
Abstract In this talk, we show that the AdS-Rindler reconstruction is incomplete. CFT operators naively given by the holographic dictionary for the AdS-Rindler reconstruction contain tachyonic modes, which are inconsistent with the spectrum in the CFT side defined on the associated subregion. Therefore, the subregion duality and the entanglement wedge reconstruction do not hold. In addition, we also show that the tachyonic modes are related to null geodesics connecting the past and future horizons.

Date/Place December 13th (Tue.) 15:40-16:40 / Hybrid (H701 + Online)
Name David Ward
　Title　 Investigation of a new Spin Glass Order Parameter in SU(2) Gauge-Higgs in Five Dimensions
Abstract A recently proposed order parameter, analogous to the Edwards-Anderson order parameter of the spin glass, was shown to detect a symmetry breaking transition between the Higgs and QCD like phases of an SU(2) gauge-Higgs in D=4. A stronger criterion for confinement termed "separation of charge" was proposed to distinguish phases with an unbroken global custodial symmetry. This order parameter has been shown to detect the breaking of this global custodial symmetry between the confinement and Higgs like regions, but has not been tested for additional phases which also maintain unbroken custodial symmetry. In this talk I will cover the SU(2) gauge-Higgs theory in D=5 which contains a massless phase and present the behavior of this order parameter with a massless phase present. I will also present the phase diagram associated with this field theory and discuss how this order parameter may be applied to lattice monte carlo simulations.

Date/Place December 6th (Tue.) 15:40-16:40 / Hybrid (H701 + Online)
Name Koji Tsumura (Kyushu U.)
　Title　 Baryon and Lepton number nonconservation as Peccei-Quinn mechanism
Abstract Baryon and lepton numbers are accidental symmetries in the standard model, while Peccei-Quinn symmetry is hypothetical symmetry which is introduced to solve the strong CP problem. We study the possible connections between Peccei-Quinn symmetry and baryon/lepton number symmetries. This framework identifies an axion as the Nambu-Goldstone boson of baryon/lepton number violations. As a result, characteristic baryon/lepton number violating processes are predicted. We developed the general method to determine the baryon number and lepton number of new scalar bosons in the axion model.

Date/Place November 29th (Tue.) 15:40-16:40 / Hybrid (H701 + Online)
Name Masataka Watanabe (YITP)
　Title　 Callan-Rubakov effect and non-invertible defects
Abstract There is a famous puzzle in QED coupled to N massless Dirac fermions that the scattering of a fermion off a monopole creates an out-state which cannot be any of the elementary particles in the theory. We give a new understanding of the s-wave reduced version of the phenomena by interpreting the magnetic defect as a Tambara-Yamagami line defect.

Date/Place November 22th (Tue.) 15:40-16:40 / Hybrid (H601 + Online)
Name Heng-Yu Chen (National Taiwan U.)
　Title　 Explicit Late Time Correlation Functions in de Sitter from CFT
Abstract In this talk, we will discuss recent work on constructing an explicit example of dS3/CFT2 correspondence via analytic continuation, then we will use it to obtain the late time correlation functions in the three dimensional de Sitter spacetime from two dimensional CFT. We will also discuss how to reproduce them from the suitable holographic configurations, and future directions.

Date/Place November 8th (Tue.) 15:40-16:40 / Online
Name Nobuyuki Matsumoto (RIKEN / BNL) (Slides)
　Title　 Comment on the subtlety of defining real-time path integral in lattice gauge theories
Abstract Recently, Hoshina, Fujii, and Kikukawa [1] pointed out that the naive lattice gauge theory action in Minkowski signature does not result in a unitary theory in the continuum limit, and Kanwar and Wagman [2] proposed alternative lattice actions to the Wilson action without divergences. We here show that the subtlety can be understood from the asymptotic expansion of the modified Bessel function, which has been discussed for path integral of compact variables in nonrelativistic quantum mechanics [3,4]. The essential ingredient for defining the appropriate continuum theory is the iε prescription, which we show is applicable also for the Wilson action. It is here important that the iε should be implemented for both timelike and spacelike plaquettes. We then argue that such iε can be given a physical meaning that they remove singular paths having nontrivial winding for an infinitesimal time evolution that do not have corresponding paths in the continuum. Such point of view is only apparent in systems with compact variables as lattice gauge theories. This talk is based on [5].

[1] H. Hoshina, H. Fujii and Y. Kikukawa, "Schwinger-Keldysh formalism for Lattice Gauge Theories," PoS LATTICE2019, 190 (2020)
[2] G. Kanwar and M. L. Wagman, "Real-time lattice gauge theory actions: Unitarity, convergence, and path integral contour deformations," Phys. Rev. D 104, no.1, 014513 (2021) [arXiv:2103.02602 [hep-lat]]
[3] W. Langguth and A. Inomata, "Remarks on the Hamiltonian path integral in polar coordinates," J. Math. Phys. 20, 499-504 (1979)
[4] M. Bohm and G. Junker, "Path integration over compact and noncompact rotation groups," J. Math. Phys. 28, 1978-1994 (1987)
[5] N. M. "Comment on the subtlety of defining real-time path integral in lattice gauge theories," [arXiv:2206.00865 [hep-lat]]

Date/Place November 1st (Tue.) 15:40-16:40 / Hybrid (H701 + Online)
Name Katsumasa Nakayama (RIKEN) (Slides)
　Title　 Tensor renormalization group analysis for the phase structure of the CP(1) model with the theta term.
Abstract We study the phase structure of the CP(1) model by using several kinds of the tensor renormalization group. The phase structure of the CP(1) model is investigated by the strong coupling expansion, analytical continuation with the assumption, possibly sign problematic Monte Carlo simulation and the simple TRG. These predictions show the first-order transition at θ = π at the strong coupling region, but there are contradicted in the weak and intermediate coupling region because of the limitation of the systematic error. In this work, we extend the TRG method to the intermediate coupling region by carefully discussing the systematic error in TRG. We apply the recently developed TRG method, such as the anisotropic TRG and bond-weighted TRG, to reduce the systematic errors in the coarse-graining step. In order to show the importance of systematic error estimation, we start from the θ = 0 calculation as a demonstration. The larger bond size is strongly required for a reliable result, depending on the initial tensor size. After the demonstration, we calculate the CP(1) model with the theta term. With the controlled systematic error, the TRG method shows the first order transition at the θ = π up to β < 1.1 .

Date/Place October 25th (Tue.) 15:40-16:40 / Hybrid (H701 + Online)
Name Naoto Kan (Osaka U.)
　Title　 Effective field theory in light of relative entropy
Abstract We consider the relative entropy between two theories (or systems) described by heavy and light degrees of freedom. The non-negativity of the relative entropy gives inequalities for the difference between the two EFTs obtained by integrating the heavy degrees of freedom.　 Using the inequalities, we consider the entropy constraint on higher-dimensional operators arising from integration over the heavy degrees of freedom.

Date/Place October 18th (Tue.) 15:40-16:40 / Online
Name Yuichi Uesaka (Kyushu Sangyo U.) (Slides)
　Title　 Models of the muonium to antimuonium transition
Abstract Muonium is a bound state composed of an antimuon and an electron, which constitutes a hydrogen-like atom. The process of the muonium-to-antimuonium transition is considered to be effective to identify fundamental interactions which relate to the lepton flavor and lepton number violation. New experiments are being planned at J-PARC in Japan and CSNS in China, and it is expected to attract more attention in the near future. We have studied what kind of model can be verified in the next generation of the muonium-to-antimuonium transition search experiments while escaping the constraints by other experiments. Though the transition probability is strongly suppressed by the lepton flavor conservation in the standard model, it can be much larger by the exchanges of neutral and doubly charged bosons, and by box loop diagrams in new physics beyond the standard model. In this talk, I will show the analyses for some neutrino models which can be tested in the forthcoming experiments for the muonium to antimuonium transition.

Date/Place October 11th (Tue.) 15:40-16:40 / Hybrid (H701 + Online)
Name Tatsuhiro Misumi (Kinki U.) (Slides)
　Title　 Lattice fermions as spectral graphs -Toward a new theorem-
Abstract We study lattice fermions from the viewpoint of spectral graph theory (SGT). We find that a fermion defined on a certain lattice is identified as a spectral graph. SGT helps us investigate the number of zero eigenvalues of lattice Dirac operators even on the non-torus and non-regular lattice, leading to understanding of the number of fermion species (doublers) on lattices with arbitrary topologies. We apply this idea to the known lattice fermion formulations including Naive fermions, Wilson fermions and Domain-wall fermions, and reproduce the known fact on the number of species. We also apply it to the lattice fermion on the discretized four-dimensional hyperball and discuss the number of fermion species on the bulk. In the end of the paper, we discuss the application of the analysis to lattice fermions on generic lattices with arbitrary topologies, leading to conjecturing a new theorem regarding the number of fermion species on the lattice.

Date/Place October 4th (Tue.) 15:40-16:40 / Hybrid (H701 + Online)
Name Sinya Aoki (YITP) (Slides)
　Title　 Is energy conserved in general relativity ?
— Noether’s 1st theorem with local symmetries —
Abstract To answer the question in the title is rather non-trivial. In a flat spacetime, as a consequence of Noether's 1st theorem, a time translation symmetry not only defines a corresponding energy density as the time component of the Noether current, but also tells that a total energy given by a volume integral of the energy density is conserved. This construction of a conserved energy does not work in general relativity, since a time translational symmetry is a part of local symmetries, general coordinate transformations, to which Noether's first theorem can not be directly applied. Recently we propose a general method to derive a conserved current associated with a global symmetry which is a part of local symmetries. We apply the method to general relativity and obtain the following answer to the question. “No, the matter energy is not conserved in general. However there always exist a more general conserved charge associated with matters.” In my talk, I will explain how this conclusion is derived.

Date/Place August 9th (Tue.) 15:40-16:40 / Hybrid (H701 + Online)
Name Florentin Jaffredo (Université Paris-Saclay, IJCLAB)
　Title　 B anomalies at low and high energy
Abstract Results from LHCb and B-factories hint at violation of Lepton Flavor Universality (LFU) in both charged and neutral B-meson decays. We start by discussing the impact of the recent observation of the Lambda_b to Lambda_c tau nu decay on these anomalies and the perspectives it offers in terms of new observables that can be extracted from angular distributions. We will then compare those low energy observables to the constraints that can be obtained from the Drell-Yan processes pp->lnu and pp->ll at high transverse momentum, both in the framework of Effective Field Theory and with explicit O(1 TeV) Leptoquark Mediators.

Date/Place August 2nd (Tue.) 15:40-16:40 / Online
Name Graham White (IPMU) (Slides)
　Title　 Clearing the fog on CP violating sources during a cosmic phase transition
Abstract A key question next generation colliders and gravitational wave detectors will investigate is the nature of electroweak symmetry breaking. If Universe boils when the Higgs obtains a vev, conditions are right to explain one of the profoundest mysteries motivating physics beyond the Standard Model - why there is more matter than anti-matter. Unless conditions are extremely unfavourable, it is difficult to make robust statements about the viability of a parameter point within a model as different methods of estimating the yield of baryon asymmetry generated during a phase transition differ by many orders of magnitude. This problem has been outstanding for three decades. I demonstrate that one popular method of calculation is invalid, whereas qualitatively similar effects can be derived from another source.

Date/Place July 26th (Tue.) 15:40-16:40 / Hybrid (H701 + Online)
Name Yu Hamada (KEK) (Slides)
　Title　 Coleman-Weinberg Abrikosov-Nielsen-Olesen strings
Abstract Vortex strings are topological solitons in field theories and appear in various systems, such as superconductor, neutron star, early universe and so on. We clarify the nature of vortex strings in the Abelian-Higgs-like model with a Coleman-Weinberg type Higgs potential, which is inspired by the argument of the naturalness problem in particle physics. This model has the gauge U(1) symmetry and the classical scale invariance. The model has no vortex string solution at the classical level, while quantum corrections spontaneously break the U(1) symmetry and stable vortex strings exist. The interaction between the two vortex strings is found to be very different from that of the Abelian-Higgs model with the conventional second- and fourth-order type potentials. Implications for particle physics and cosmology are also discussed.

Date/Place July 19th (Tue.) 15:40-16:40 / Hybrid (H701 + Online)
Name Arindam Das (Hokkaido U.)
　Title　 Connecting energy, intensity and cosmic frontiers through neutrino
Abstract The mystery of tiny neutrino mass is an unsolved problem leading to the avenues like beyond the standard model (BSM) physics. There are interesting aspects when standard model (SM) is extended by particles and/ or gauge groups which involve a variety of mechanisms to explain the origin of tiny neutrino mass. The cost of gauge extension of the SM introduces charged and neutral gauge bosons in the theory which play important roles in the neutrino phenomenology. In this talk we will discuss a gauge extension of the SM which not only reproduces the tiny neutrino mass through the seesaw mechanism, but also involves a neutral gauge boson interaction which plays important roles in the intensity, lifetime, energy and cosmic frontiers. Such gauge bosons can be probed in the future experiments.

Date/Place July 5th (Tue.) 15:40-16:40 / Hybrid (H701 + Online)
Name Chris Lau (Kobe U.) (Slides)
　Title　 Emergence of time from unitary equivalence
Abstract In this talk, I want to motivate a possible way to realise time as an emergent concept. I will introduce a general fermionic system and demonstrate how a modular flow can be interpreted as a physical time flow. I will provide support for this interpretation using the thermofield double state together with the relations between various quantum chaos diagnostic quantities. I will explain how these concepts can be linked together and realise an emergence of time. I will end by discussing some limitations of our example.

Date/Place June 21th (Tue.) 15:40-16:40 / Hybrid (H701 + Online)
Name Teppei Kitahara (Nagoya U.)
　Title　 The W-boson mass anomaly and new physics interpretation
Abstract The CDF collaboration recently announced the most precise measurement of the W-boson mass by using the proton-antiproton collision data at the Fermilab Tevatron. This data provides a significant inconsistency between the measured mass and the Standard Model prediction. In this talk, first, I will summarize the current circumstances of the W-boson mass measurements and the Standard Model prediction. Next, I will present several explanations of this anomaly by the new physics beyond the Standard Model. Finally, a model with the vector-like quark will be introduced, based on our recent work arXiv:2204.05962.

Date/Place June 17th (Fri.)　15:40-16:40 / Hybrid (H701 + Online)
Name Motoi Endo (KEK) (Slides)
　Title　 Muon g-2
Abstract In the last year, the Fermilab experiment has reported their first result on the measurement of the muon anomalous magnetic moment (g-2). The result was consistent with the Brookhaven E821 experiment, and the deviation from the standard model prediction becomes 4.2sigma, which is planned to be revised soon. In this talk, we will overview the status and prospect of the theoretical side of the muon g-2. I will first review the standard model prediction and explain the issues explored today. Then, new physics interpretations will be discussed, especially focusing on the supersymmetric models.

Date/Place June 7th (Tue.) 15:40-16:40 / Hybrid (H701 + Online)
Name Shinichiro Yahagi (Tokyo U.) (Slides)
　Title　 Narain CFTs and error-correcting codes
Abstract A Narain CFT is a conformal field theory (CFT) that describes a compactified spacetime. On the other hand, an error-correcting code is a concept in information theory for transmitting information correctly in spite of errors. In this talk, I will discuss the relation between Narain CFTs and error-correcting codes on finite fields through lattices. Using this correspondence, we can consider the spectrum and the symmetries of the CFT in the language of the code. In particular, the spectral gap of the CFT and the error correction capability of the code are roughly proportional, which helps to find CFTs with large spectral gaps.

Date/Place May 31th (Tue.) 15:40-16:40 / H701
Name Kohei Fujikura (Kobe U.) (Slides)
　Title　 Microlensing constraints on axion stars including finite lens and source size effects
Abstract Axions are prominent cold dark matter candidates and may form gravitationally bound clumps, called “axion stars”. Such massive objects can cause an amplification of brightness of a background source star when it passes close to a line-of-sight to that star, called gravitational microlensing events. Therefore, the abundance of axion stars can be constrained by observations of microlensing events such as the EROS-2 survey and the Subaru Hyper Suprime-Cam observation. We compute the expected number of microlensing events of stars composed of the ordinary QCD axion and axion-like particles, and derive microlensing constraints including an effect of the extended structure. In this talk, I will mainly review the basics of axion stars and explain microlensing constraints on compact objects that possess extended structures.

Date/Place May 24th (Tue.) 15:40-16:40 / H701
Name Kodai Sakurai (Tohoku U.) (Slides)
　Title　 Implications of anomaly-free axion for Higgs bosons in 3HDM
Abstract Axion (or axion-like particle) is a prominent candidate of light dark matter (DM). It emerged as the pseudo Nambu-Goldstone boson originated from the breaking of global U(1) symmetry. If the mass scale is keV, axion usually suffers from the severe constraint from the X-ray bounds. However, a fascinating axion, which can evade such a severe constraint, was proposed as an anomaly-free axion. In this talk, I will discuss a three Higgs doublet model (3HDM) as a UV complete model where the anomaly-free axion is embodied. I will show the synergy between the anomaly-free axion and the heavy Higgs bosons predicted in this concrete model.

Date/Place May 18th (Web.) 12:10-13:10 /Hyblid (Online + H701)
Name Yoshitaka Okuyama (Tokyo U. and Osaka U.) (Slides)
　Title　 Method of images in defect conformal field theories
Abstract We propose a prescription for describing correlation functions in higher-dimensional defect conformal field theories (DCFTs) by those in ancillary conformal field theories (CFTs) without defects, which is a vast generalization of the image method in two-dimensional boundary CFTs. A correlation function of n operators inserted away from a defect in a DCFT is represented by a correlation function of 2n operators in the ancillary CFT, each pair of which is placed symmetrically with respect to the defect. For scalar operators, we establish the correspondence by matching the constraints on correlation functions imposed by conformal symmetry on both sides. Our method has potential to shed light on new aspects of DCFTs from the viewpoint of conventional CFTs.

Date/Place May 10th (Tue.) 15:40-16:40 /Hyblid (Online + D501)
Name Linhao Li (Tokyo U.) (Slides)
　Title　 Symmetry Protected Topological Criticality
Abstract Symmetry protected topological (SPT) phases are one of the simplest, yet nontrivial, gapped systems that go beyond the Landau paradigm. In this work, we study the notion of SPT for critical systems, namely, symmetry protected topological criticality (SPTC). We discuss a systematic way of constructing a large class of SPTCs using decorated defect construction, study the physical observables that characterize the nontrivial topological signatures of SPTCs, and discuss the stability under symmetric perturbations. Our exploration of SPTC is mainly based on several previous studies of gapless SPT: gapless symmetry protected topological order, symmetry enriched quantum criticality and intrinsically gapless topological phases. We partially reinterpret these previous studies in terms of decorated defect construction, and discuss their generalizations.

Date/Place April 26th (Tue.) 15:40-16:40 /H501
Name Tatsuma Nishioka (Osaka U.) (Slides)
　Title　 CFT duals of three-dimensional de Sitter gravity
Abstract We present a class of dS/CFT correspondence between two-dimensional CFTs and three-dimensional de Sitter spaces. We argue that such a CFT includes an SU(2) WZW model in the critical level limit k → −2, which corresponds to the classical gravity limit. We can generalize this dS/CFT by considering the SU(N) WZW model in the critical level limit k →−N, dual to the higher spin gravity on a three-dimensional de Sitter space. We confirm that under this proposed duality the classical partition function in the gravity side can be reproduced from CFT calculations.

Date/Place April 19th (Tue.) 15:40-16:40 /H701
Name Tanmoy Mondal (Osaka U.) (Slides)
　Title　 Some phenomenological aspects of 2HDM
Abstract I will talk about some phenomenological aspects of the two Higgs doublet model(2HDM). The 2HDM can explain the muon anomalous magnetic moment with a light pseudoscalar. I will discuss the prospect of discovering such particles at the lepton collider like ILC. Then I will discuss how an extension of 2HDM can connect neutrino mass and muon anomalous magnetic moment.

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