Back Numbers 2020-21
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  • May 29, 2020, 13:30
  • Speaker: Osamu Seto (Hokkaido Univ.)
    Title Self-interacting neutrino models
    E-Print [1] Planck (2018), [arXiv:1807.06209[astro-ph]]
    [2] C. D. Kreisch, F.-Y. Cyr-Racine, O. Doré, [arXiv:1902.00534[astro-ph]]
    [3] K. Lyu, E. Stamou, L.-T. Wang, [arXiv:2004.10868[hep-ph]]
    [4] M. Berbig, S. Jana, A. Trautner, [arXiv:2004.13039[hep-ph]]


  • June 12, 2020, 13:30
    Speaker: Kazuhiko Suehiro
    Title On the Nelson-Seiberg theorem: generalizations and counter-examples
    E-Print [1] A. Amarti, D. Sauro [arXiv:2005.02076[hep-th]]

  • June 26, 2020, 13:30
    Speaker: Morimitsu Tanimoto (Niigata Univ.)
    Title Modular Symmetry for Quarks and Leptons - CKM and PMNS at nearby fixed points -
    Abstract The origin of flavors of quarks and leptons is one of important issues in particle physics. Indeed, a lot of works have been presented by using the discrete groups for flavors to understand the flavor structures of quarks and leptons. Recently, a new approach to the flavor problem appeared based on the invariance of the modular group, and then, an interesting framework for the construction of flavor models has been put forward based on the finite modular groups. If flavors of quarks and leptons are originated from a same two-dimensional compact space, quarks and leptons have same flavor symmetry and the common modulus tau. Therefore, it is challenging to reproduce observed CKM mixing angles and the CP violating phase while observed PMNS are also reproduced in the lepton sector with the common tau. This work provides a new aspect for the unification of quarks and leptons. At first, I give the introductory talk of this new approach, and then, I present our recent work based on the A4 modular symmetry for quarks and leptons. Especialy, I discuss on the flavor structure at nearby fixed points, which leads to clear predictions.
    E-Print [1] H. Okada, H. Maeda, M. Tanimoto, [arXiv:2005.00775[hep-ph]]
    [2] H. Okada, H. Maeda, M. Tanimoto, [arXiv:1905.13421[hep-ph]]


  • July 3, 2020, 13:30
    Speaker: Yoshiki Uchida (Nagoya Univ.)
    Title Generalization of Higgs effective field theory
    Abstract Higgs effective field theory (HEFT) is the most general effective field theory consists of the standard model (SM) fields. Though HEFT is quite useful to describe the deviation from the SM, it has some defects: because the heavy new particles are integrated out, much information about the properties of new particles (such as production cross section) are lost. In this talk, I will formulate a generalization of HEFT (GHEFT) including arbitrary number of new scalar particles. Thanks to GHEFT, we can predict or constrain the properties of extra scalar fields in model-independent manner. Focusing the geometry of the GHEFT scalar sector, we find that some electroweak precision observables are deeply related to the perturbative unitarity of the GHEFT. This talk is based on arXiv:1904.07618.
    E-Print [1] R. Nagai, M. Tanabashi, K. Tsumura, Y. Uchida, [arXiv:1904.07618[hep-ph]]

  • July 10, 2020, 13:30
    Speaker: Kinya Oda (Osaka Univ.)
    Title Dynamically emergent gravity from hidden local Lorentz symmetry
    Abstract Gravity can be regarded as a consequence of local Lorentz (LL) symmetry, which is essential in defining a spinor field in curved spacetime. The gravitational action may admit a zero-field limit of the metric and vierbein at a certain ultraviolet cutoff scale such that the action becomes a linear realization of the LL symmetry. Consequently, only three types of term are allowed in the four-dimensional gravitational action at the cutoff scale: a cosmological constant, a linear term of the LL field strength, and spinor kinetic terms, whose coefficients are in general arbitrary functions of LL and diffeomorphism invariants. In particular, all the kinetic terms are prohibited except for spinor fields, and hence the other fields are auxiliary. Their kinetic terms, including those of the LL gauge field and the vierbein, are induced by spinor loops simultaneously with the LL gauge field mass. The LL symmetry is necessarily broken spontaneously and hence is nothing but a hidden local symmetry, from which gravity is emergent.
    E-Print [1] S. Matsuzaki, S. Miyawaki, K. Oda, M. Yamada, [arXiv:2003.07126[hep-th]]

  • July 17, 2020, 14:30
    Speaker: Hiroyuki Ishida (KEK)
    Title How to hunt 140 MeV ALP?
    Abstract In this talk, we propose a novel probes for 140 MeV axion-like particle (ALP) which usually suffers from huge backgrounds of neutral pion. Especially the time-dependent CP asymmetry in \(B^0 \rightarrow K^0_S \pi^0 \gamma\) process and \(B \rightarrow e\) mu process have a potential to hunt the elusive signal. We show contributions to leptonic flavor observables as well.
    E-Print [1] H. Ishida, S. Matsuzaki, Y. Shigekami, [arXiv:2006.02725[hep-ph]]

  • July 31, 2019, 13:30
    M2 Journal club
    Speaker: Chikara Tateshita (Hokkaido Univ.)
    Title Application of modular flavor symmetry to mixing angles of quark and lepton


  • August 7, 2020, 14:30
    Speaker: Koji Hahimoto (Osaka Univ.)
    Title Deep learning and holography
    Abstract After briefly reviewing deep learning and its application to physics problems, I shall discuss the relation between the holographic principle and deep learning. To find a gravity dual for a given quantum field theory is an inverse problem, and we apply the machine learning approach to the inverse problem. QCD data such as chiral condensate produces an emergent geometry, with which we can calculate Wilson loop as a prediction.
    E-Print [1] K. Hashimoto, H.-Y. Hu, Y.-Z. You, [arXiv:2006.00712[hep-th]]
    [2] T. Akutagawa, K. Hashimoto, T. Sumimoto, [arXiv:2005.02636[hep-th]]
    [3] K. Hashimoto, [arXiv:1903.04951[hep-th]]
    Phys. Rev. D 99, 106017 (2019)
    [4] K. Hashimoto, S. Sugishita, A. Tanaka, A. Tomiya, [arXiv:1809.10536[hep-th]]
    Phys. Rev. D 98, 106014 (2018)
    [5] K. Hashimoto, S. Sugiyama, A. Tanaka, A. Tomiya, [arXiv:1802.08313[hep-th]]
    Phys. Rev. D 98, 046019 (2018)


  • October 9, 2020
    M2 Journal club, 10:30
    Speaker: Shota Kikuchi (Hokkaido Univ.)
    Title Modular symmetry for wavefunctions on magnetized \(T^2 \times T^2\)
    Journal club, 13:30
    Speaker: Hisao Suzuki (Hokkaido Univ.)
    Title Humanly traversable wormholes

  • October 16, 2020, 14:00
    Speaker: Soichiro Hashiba (RESCEU)
    Title Gravitational production of right-handed neutrinos after quintessential inflation
    Abstract Incorporating three generations of right-handed Majorana neutrinos to quintessential inflation (inflation model in which the inflaton continues rolling even after inflation and also drives late time accelerating cosmic expansion [1]), we have constructed a model which simultaneously explains inflation, dark energy, reheating, dark matter and baryogenesis. These right-handed neutrinos have somewhat hierarchical masses and the heaviest, the intermediate and the lightest one account for reheating, CP violation of leptogenesis, and dark matter, respectively. Although this setup looks almost the same as split seesaw [2], we adopt gravitational particle production [3] instead of production from SM plasma. In this mechanism, right-handed neutrinos are produced by the gravitational particle production, induced by a time-varying metric in the kination regime after inflation. This talk is mainly based on our recent paper [4].
    e-print [1] P.J.E. Peebles, A. Vilenkin, [arXiv:astro-ph/9810509[astro-ph]]
    Phys. Rev. D 59, 063505 (1999)
    [2] A. Kusenko, F. Takahashi, T. Yanagida, [arXiv:1006.1731[hep-ph]]
    Phys. Lett. B 693, 144 (2010)
    [3] Phys. Rev. 183, 1057,(1969)
    [4] S. Hashiba, J. Yokoyama, [arXiv:1905.12423[hep-ph]]
    Phys. Lett. B 798, 135024 (2019)

  • October 23, 2020, 13:30
    Speaker: Masaki J. S. Yang (Saitama Univ.)
    Title Flavor structure and discrete symmetry
    Abstract Recent observations of neutrino oscillation suggest some remnant symmetry of the neutrino mass matrix. In this seminar, we discuss several flavor texture of quarks and leptons and relation to discrete symmetry, such as μ-τ symmetry. After that, we present a recent study on the μ-τ reflection, universal four-zero texture, and generalized CP symmetry.
    e-print [1] H. Fritzsch, Z-z. Xing, [arXiv:hep-ph/9912358[hep-ph]]
    [2] Z-z. Xing, Z-h. Zhao, [arXiv:1512.04207[hep-ph]]

  • October 30, 2020, 15:00
    Speaker: Kenichi Saikawa (Kanazawa Univ.)
    Title Cosmological aspects of the QCD axion
    Abstract The axion is a well-motivated hypothetical particle as it arises as a solution to the strong CP problem of QCD and is regarded as a good candidate for cold dark matter. In this seminar talk, we discuss some cosmological aspects of the QCD axion. The seminar is composed of two parts: In the first part, we review the issue of the relic abundance of dark matter axions produced from strings and present some preliminary results of ongoing large scale numerical simulations on the cosmological evolution of axionic strings. In the second part, we focus on a minimal kind of embedding of inflation into the axion framework, called the Standard Model-Axion-Seesaw-Higgs portal inflation (SMASH) model. We point out that the SMASH model gives a non-trivial and unique prediction for the nature of the second order Peccei-Quinn phase transition, which is imprinted on the spectrum of primordial gravitational waves (GWs) in a frequency range relevant to future high-sensitivity GW experiments.
    e-print [1] E. Armengaud et al., [arXiv:1904.09155[hep-ph]]
    JCAP 06 (2019) 047
    [2] A. Ringwald, K. Saikawa, C. Tamarit, [arXiv:2009.02050[hep-ph]]


  • November 13, 2020, 10:30, 13:00
    Speaker: Kotaro Tamaoka (Kyoto Univ.)
    Title Pseudo Entropy and Holography
    Abstract We introduce a new information-theoretic quantity, called pseudo entropy. We argue the pseudo entropy is a generalization of the entanglement entropy to a virtual post-selection process and is holographically dual to the area of the minimal surface in Euclidean “time-dependent” background. If time permitting, we also discuss its field theory analysis. In the review part, we overview the background to understand the discussion of pseudo entropy in detail.
    e-print [1] Y. Nakata, T. Takayanagi, Y. Taki, K. Tamaoka, Z. Wei, [arXiv:2005.13801[hep-th]]

  • November 20, 2020, 10:30, 13:30
    Speaker: Yuki Yokokura (RIKEN)
    Title Black Hole as a Quantum Field Configuration
    Abstract In quantum theory, black holes evaporate. We develop this property as the 0th approximation and provide a field-theoretic description of black holes. We find a spherically symmetric self-consistent solution of the metric and state of the semi-classical Einstein eq coupled with N massless scalar quantum fields. Here, the metric is locally \(AdS_2\) \(S^2\) geometry, and the bound modes are in the ground state of the matter fields in the metric while the continuum s-waves are excited to describe the collapsing matter and Hawking radiation with the ingoing negative energy flow. This object is supported by a large tangential pressure due to the vacuum fluctuation of the bound modes with large angular momenta. This describes the interior of the black hole when the back reaction of the evaporation is considered. The black hole is a compact object with a surface (instead of horizon) that looks like a conventional black hole from the outside and eventually evaporates without a singularity. [arxiv:2002.10331] (Before this main talk, I give a review on Hawking radiation.)
    e-print [1] H. Kawai, Y. Yokokura, [arXiv:2002.10331[hep-th]]
    Rehearsal of M1 Journal club, 16:00
    Speaker: Yuya Ogawa (Hokkaido Univ.)
    Title String theory and realizing for generations in the standard model

  • November 27, 2020, 15:00
    Speaker: Shinji Tsujikawa (Waseda Univ.)
    Title Introduction to scalar-tensor theories and the application to cosmology
    Abstract We review the basics of scalar-tensor theories paying paricular attention to Horndeski theories with second-order field equations of motion. In Horndeski theories we derive the perturbation equations without fixing gauges and apply them to the physics of inflation and dark energy. Our general formulation of cosmological perturbations can be used to distinguish between the models from the observations of CMB etc. We show that there exist dark energy models in Horndeski theories showing the better fit to the data in comparion to the \(\Lambda\)CDM model. Finally, we briefly mention the application of scalar-tensor theories to the physics of black holes and neutron stars.
    e-print [1] R. Kase, S. Tsujikawa, [arXiv:1809.08735[gr-qc]]
    Int. J. Mod. Phys. D 28, no.05, 1942005 (2019)
    [2] S. Peirone, G. Benevento, N. Frusciante, S. Tsujikawa, [arXiv:1905.05166[astro-ph]]
    Phys. Rev. D 100, no.6, 063540 (2019)
    [3] R. Kase, S. Tsujikawa, [arXiv:1906.08954[gr-qc]]
    JCAP 09, 054 (2019)


  • December 4, 2020, 13:30
    Speaker: Toyokazu Sekiguchi (KEK)
    Title Early recombination meets closed Universe: more than a solution to the \(H_0\) tension
    Abstract The discrepancy in measurements of the Hubble-Lemaitre constant (\(H_0\)) is the most notable anomaly in contemporary cosmology with significance as large as 6\(\sigma\). Despite many attempts, there is yet no compelling solution to the \(H_0\) tension. In the first part of my talk, I review the \(H_0\) tension. In particular, I will clarify why it is so diffcult to solve the tension. In the latter part, I will present our model, which is based on modified recombination in a closed Universe. Starting from general discussion on necessary conditions that successful modified recombination models should satisfy to fit CMB observations, I will demonstrate time-varying me models indeed satisfy those conditions. To fit low-\(z\) distance measurements such as baryon acoustic oscillation and type-Ia supernovae, a positive spatial curvature plays an essential role. Compared to the canonical \(\Lambda\)CDM, our model improves the chi-square by more than 23. We also show our model solves the lensing anomaly in Planck data concurrently.
    Rehearsal of M1 Journal club, 10:30
    Speaker: Yo Toda (Hokkaido Univ.)
    Title Observation and Theory of Dark Energy

  • December 11, 2020, 13:30
    Speaker: Yuji Sugawara (Ritsumeikan Univ.)
    Title Non-SUSY String Vacua with Vanishing Cosmological Constant
    Abstract Motivated by the cosmological constant problem, I discuss the constructions of non-supersymmetric string vacua with vanishing 1-loop cosmological constant. I especially focus on my recent studies on the constructions of non-SUSY string vacua with the bose-fermi cancellation (i.e. the vanishing torus partition functions) based on the asymmetric orbifolds of generic Gepner models for Calabi-Yau 3-folds. I would also like to discuss the possibility of vanishing cosmological constant WITHOUT the bose-fermi cancellation (i.e. non-zero partition function), which is a work in progress in collaboration with Prof. Yuji Satoh.
    Rehearsal of M1 Journal club, 15:30
    Speaker: Kaito Nasu (Hokkaido Univ.)
    Title Computation of Yukawa Couplings from String Theory

  • December 15, 2020
    Rehearsal of M1 Journal club, 13:30
    Speaker: Kouki Hoshiya (Hokkaido Univ.)
    Title Basic Concepts of the String Theory


  • January 8, 2021, 13:30
    Speaker: Yoshihiko Abe (Kyoto Univ.)
    Title Electroweak Axion String and Superconductivity
    Abstract We study the axion strings with the electroweak gauge flux in the DFSZ axion model and show that these strings, which we call the electroweak axion strings, can exhibit superconductivity without fermionic zero modes. In this talk, I review the (axion) strings and superconducting strings, then discuss three types of electroweak axion string solutions constructed in this work. Among them, the string with \(W\)-flux can be lightest in some parameter space, which leads to a stable superconducting cosmic axion string. I also show that a large electric current can flow along the string due to the Peccei-Quinn scale much higher than the electroweak scale. This large current induces a net attractive force between the axion strings, which implies a new possibility that the axion strings form Y-junctions in the early universe. This talk is based on the work with Yu Hamada and Koichi Yoshioka, arXiv:2010.02834[hep-ph].
    e-print [1] Y.Abe, Y.Hamada, K.Yoshioka, [arXiv:2010.02834 [hep-ph]]
    Rehearsal of Journal club, 10:30
    Speaker: Akihiko Jo (Hokkaido Univ.)
    Title Perturbative picture of the string theory

  • January 15, 2021, 13:30
    Speaker: Masaki Honda (Waseda Univ.)
    Title Towards computing Yukawa couplings from magnetized Riemann surface of higher genus
    Abstract Magnetized extra dimensional models are successful models to explain the chiral structure and the generation structure in the standard model. In a magnetized extra dimensional model, we can explain those structures formally by the index theorem. However, we have to derive the zero modes of the Dirac operator to compute coupling constants for applications. For a two dimensional orientable compact manifold, they are derived and computed only for the sphere and the torus, not for a Riemann surface of higher genus. Then we show the construction of a Dirac operator on a magnetized Riemann surface of higher genus, the property of the zero modes, and an explicit basis of the space of the zero modes.
    e-print [1] M. Honda, [arXiv:2008.11461 [hep-th]]
    [2] H. Cohen and F. Stromberg, “Modular forms: a classical approach”, American Mathematical Society (2017).

  • January 22, 2021, 10:30
    Master thesis presentation
    Speaker: Shota Kikuchi (Hokkaido Univ.)
    Title Classification of three generation models by orbifolding magnetized \(T^2\times T^2\)

  • January 29, 2021, 10:30
    Rehearsal of Master thesis presentation
    Speaker: Shota Kikuchi (Hokkaido Univ.)
    Title Classification of three generation models by orbifolding magnetized \(T^2\times T^2\)