Back Numbers 2021-22
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April
  • April 16, 2021
    • Speaker: Shin-Yen Tseng (Tokyo Univ.)
    Title Minimal gauged U(1)$_{L_\mu - L_\tau}$ model, leptogenesis, and the sign of cosmological baryon asymmetry
    E-Print [1] K. Asai, K. Hamaguchi, N. Nagata, Shin-Yen Tseng, [arXiv:2005.01039[hep-ph]]
    [2] K. Asai, K. Hamaguchi, N. Nagata, [arXiv:1705.00419[hep-ph]]
    [3] T. Araki, J. Heeck, J. Kubo, [arXiv:1203.4951[hep-ph]]
    [4] P.H. Frampton, S.L. Glashow, T. Yanagida, [arXiv:hep-ph/0208157[hep-ph]]
  • April 23, 2021
    • Speaker: Shigeki Sugimoto (Kyoto Univ.)
    Title Anomaly of fermions with spacetime dependent mass
    Abstract In this talk, we discuss perturbative anomaly of fermions with spacetime dependent mass. We show that the anomaly can be written by the Chern character of a superconnection introduced by Quillen in 1985 and discuss its applications to systems with interfaces and spacetime boundaries.





    May
  • May 7, 2021
    • Speaker: Mayumi Aoki (Kanazawa Univ.)
    Title A hybrid seesaw model and hierarchical neutrino flavor structures based on A4 symmetry
    Abstract In this talk, I will discuss a hybrid seesaw model based on A4 flavor symmetry. In this model, tree-level and one-loop seesaw mechanisms predict different flavor structures in the neutrino mass matrix and generate a notable hierarchy among them. The A4 symmetry is spontaneously broken to the Z2 symmetry. A predicted dark matter will also be discussed.
  • May 21, 2021
    • Speaker: Kenzo Ishikawa (Hokkaido Univ.)
    Title Is the cross section sufficient for the scattering?
  • May 28, 2021
    • Speaker: Kensuke Akita (IBS-CTPU)
    Title Precise Cosmic Neutrino Capture
    E-Print [1] K. Akita, M. Yamaguchi, [arXiv:2005.07047[hep-ph]]
    [2] K. Akita, S. Hurwitz, M. Yamaguchi, [arXiv:2010.04454[hep-ph]]





    June
  • June 4, 2021
    • Speaker: Maki Takeuchi (Kobe Univ.)
    Title Zero-mode counting formula and zeros in orbifold compactifications
    Abstract We thoroughly analyze the number of independent zero modes and their zero points on the toroidal orbifold T2/ZN (N = 2, 3, 4, 6) with magnetic flux background, inspired by the Atiyah-Singer index theorem. We succeed in finding a zero mode counting formula by computing the number of zero modes and winding number, separately. Further, we confirm the formula without magnetic flux directly by deriving it from a trace formula as the index theorem.
    E-Print [1] M. Sakamoto, M. Takeuchi, Y. Tatsuta, [arXiv:2004.05570[hep-th]], Phys. Rev. D 102 (2020) 025008
    [2] M. Sakamoto, M. Takeuchi, Y. Tatsuta, [arXiv:2010.14214[hep-th]], Phys. Rev. D 103 (2021) 025009
  • June 11, 2021
    Speaker: Kaigo Hirao (Tokyo Univ.)
    Title Leptonic CP and flavor violations in SUSY SU(5) GUT with right-handed neutrinos
    Abstract We study leptonic CP and flavor violations in supersymmetric (SUSY) SU(5) grand unified theory (GUT) with right handed neutrinos, paying attention to the renormalization group effects on the slepton mass matrices due to the neutrino and GUT Yukawa interactions. In particular, we study in detail the impacts of the so-called Casas- Ibarra parameters on CP and flavor violating observables. The renormalization group effects induce CP and flavor violating elements of the SUSY breaking scalar mass squared matrices, which may result in sizable leptonic CP and flavor violating signals. Assuming seesaw formula for the active neutrino masses, the renormalization group effects have been often thought to be negligible as the right-handed neutrino masses become small. With the most general form of the neutrino Yukawa matrix, i.e., taking into account the Casas-Ibarra parameters, however, this is not the case. We found that the maximal possible sizes of signals of leptonic CP and flavor violating processes are found to be insensitive to the mass scale of the right-handed neutrinos and that they are as large as (or larger than) the present experimental bounds irrespective of the right-handed neutrino masses.
  • June 18, 2021
    Speaker: Arindam Das (Hokkaido Univ.)
    Title Probing the minimal U(1)X model at future electron-positron collider via the fermion pair production channel
    Abstract The general U(1) extension of the Standard Model (SM) is a well motivated scenario which has a plenty of new physics options. Such a model is anomaly free which requires to add three generations of the SM singlet right-handed neutrinos (RHNs) which naturally generates the light neutrino masses by the seesaw mechanism.This offers interesting phenomenological aspects in the model. In addition to that the model is equipped with a beyond the SM (BSM) neutral gauge boson, which interacts with the SM and BSM particles showing a variety of new physics driven signatures. After the anomaly cancellation the U(1) charge of the particles are expressed in terms of the SM Higgs doublet and the SM Higgs singlet which allows us to study the interaction of the fermions with the . In this paper we investigate the pair production mechanism of the different charged through the photon, and boson exchange processes at the electron-positron (). The angular distributions, forward-backward (A), left-right (A) and left-right forward-backward (A)asymmetries of the different charged fermion pair productions show substantial deviation from the SM results.
    E-Print [1] A. Das, P. S. Bhupal Dev, Y. Hosotani, S. Mandal, [arXiv:2104.10902[hep-ph]]
  • June 25, 2021
    Speaker: Takehiko Asaka (Nigata Univ.)
    Title The nuMSM -- the origins of neutrino masses, dark matter, and baryon asymmetry of the Universe
    Abstract The Standard Model extended by three right-handed neutrinos can potentially explain the origins of neutrino masses, dark matter, and baryon asymmetry of the Universe at the same time. The typical mass range of the right-handed neutrinos are within the reach of experiments and the direct (and indirect) tests of the model are possible. We explain this simple framework, called the nuMSM, and its recent developments.
    E-Print [1] T. Asaka, S. Blanchet, M. Shaposhnikov, [arXiv:hep-ph/0503065]
    [2] T. Asaka, M. Shaposhnikov, [arXiv:hep-ph/0505013]
    [3] T. Asaka, S. Eijima, H. Ishida, [arXiv:1606.06686 [hep-ph]]
    [4] T. Asaka, H. Okui, [arXiv:2012.13527 [hep-ph]]





    July
  • July 9, 2021
    Speaker: Shinya Kanemura (Osaka Univ.)
    Title Higgs as a Probe of New Physics
    Abstract Although a Higgs boson was discovered, the nature of the Higgs boson, the structure of the Higgs sector, the dynamics of the electroweak symmetry breaking are still unknown. They are expected to be deeply connected to the physics beyond the standard model. In addition, these properties of the Higgs sector will be thoroughly measured by current and future collider experiments such as HL-LHC and ILC, and by various flavor experiments and also by gravitational wave experiments. Therefore the Higgs physics is regarded as an important probe of new physics. In this talk, I would like to discuss various aspects of non-minimal Higgs sectors and their relationship with scenarios of new physics. In addition, we would discuss how the Higgs sector will be explored by future experiments.
  • July 16, 2021
    M2 mid term presentation
    Speaker: Akihiro Jo (Hokkaido Univ.)
    Title Introduction to the swampland program
    Speaker: Yo Toda (Hokkaido Univ.)
    Title Extra components solutions to the Hubble tension with BBN
  • July 30, 2021
    M2 mid term presentation
    Speaker: Yuya Ogawa
    Title μ-term induced by D-brane instanton effect





    September
  • September 3rd, 2021
    Speaker: Yutaka Sakamura (KEK)
    Title Time evolution of spacetime in 6D SUGRA on S^2
    Abstract The time evolution of the background spacetime is investigated in the context of 6D SUGRA compactified on the sphere. We focus on solutions that are isotropic and homogeneous in 3D space and spherically symmetric in the compact 2D space and are connected to the 4D FLRW universe at late times. By introducing the potential for the dilaton field, the compact space will be stabilized with a finite size. As an initial condition,we assume that the radiation is dominated in the whole 5D space. By numerical calculations, we check that the 3D space continue to expand while the radius of the sphere settles down to a finite value after the oscillation around the stabilized value. We find that the oscillation lasts for a long time after the transition from the 5D space to the 3D is completed.





    October
  • October 1, 2021
    M2 mid term presentation
    Speaker: Ryota Sato
    Title String Compactification
  • October 8, 2021
    Speaker: Kei Yagyu (Osaka Univ.)
    Title Dark sector as origin of tiny lepton masses and new sources of \((g-2)_{\mu}\)
    Abstract We propose a mechanism where charged lepton masses are generated at loop levels such that their smallness can naturally be explained by O(1) Yukawa couplings. This scenario can also explain the muon g-2 anomaly which has been more serious by the first result by FNAL. As an important consequence, the muon Yukawa coupling can significantly deviate from its SM prediction, and it will be tested at the High-Luminosity LHC and/or ILC.
    E-Print [1] C. Chiang, K. Yagyu, Phys. Rev. D.103.L111302 [arXiv:2104.00890 [hep-ph]]
  • October 15, 2021
    Speaker: Eung Jin Chun (KIAS)
    Title Neutrino oscillations in dark matter
  • October 22, 2021
    Speaker: Natsumi Nagata (Tokyo Univ.)
    Title Toward Direct Detection of Axions
    Abstract In this talk, I will discuss two topics regarding the direct detection of axions produced by stellar objects. In the first part, I am going to describe, “supernovascope”, namely, a proposal for using axion helioscope to detect axions from nearby supernovae. In the second part, I will show that there was an incorrect treatment in the previous calculations of the inverse Primakoff scattering rate of axions. After fixing it, we obtain a scattering cross section that is smaller by about an order of magnitude than the previous ones. I will discuss its implications for the solar/supernova axion detection.
    e-print [1] S. F. Ge, K. Hamaguchi, K. Ichimura, K. Ishidoshiro, Y. Kanazawa, Y. Kishimoto, N. Nagata, J. Zheng, JCAP 11, 059 (2020) [arXiv:2008.03924 [hep-ph]]
    [2] T. Abe, K. Hamaguchi and N. Nagata, Phys. Lett. B 815, 136174 (2021) [arXiv:2012.02508 [hep-ph]]
  • October 29, 2021
    Speaker: Hiroto Shibuya (Kanazawa Univ.)
    Title Possibility of multi-step electroweak phase transition in the two Higgs doublet models
    Abstract We discuss whether a multi-step electroweak phase transition (EWPT) occurs in two Higgs doublet models (2HDMs). The EWPT is related to interesting phenomena such as baryogenesis and a gravitational wave from it. We examine parameter regions in CP-conserving 2HDMs and find certain areas where the multi-step EWPTs occur. The parameter search shows the multi-step EWPT prefers the scalar potential with the approximate Z2 symmetry and a mass hierarchy between the neutral CP-odd and CP-even extra scalar bosons mA < mH. By contrast, the multi-step EWPT whose first step is strongly first order favors a mass hierarchy mA > mH. In addition, we compute the Higgs trilinear coupling in the parameter region where the multi-step EWPTs occur, which can be observed at future colliders. We also discuss a multi-peaked gravitational wave from a multi-step EWPT.
    e-print [1] M. Aoki, K. Komatsu, H. Shibuya [arXiv:2106.03439 [hep-ph]].





    November
  • November 5, 2021
    M2 mid term presentation
    Speaker: Ryota Sato
    Title T-duality of closed strings
    Speaker: Toponium production at the LHC
    Title Possibility of multi-step electroweak phase transition in the two Higgs doublet models
    Abstract We study reported deviations between observations and theoretical predictions associated with the production of a pair of di-leptonically decaying top quarks at the LHC, and we examine the possibility that they reflect a signal of toponium formation. We investigate the production by gluon fusion of a color-singlet spin-0 toponium \(\eta_t\) bound state of a top and anti-top quark, that then decays di-leptonically (\(gg \rightarrow \eta_t \rightarrow \bar{\ell}\ell b \bar{b} \nu \bar{\nu}\)). We find strong correlations favoring the production of di-lepton systems featuring a small angular separation in azimuth and a small invariant mass. Although toponium production only contributes to 0.8% of the total top-quark pair-production cross section at the 13 TeV LHC, there is a possibility that it can account for observed excesses in the narrow edges of phase space. We propose a method to discover toponium formation by ‘reconstructing’ both its top and anti-top quark constituents in the di-lepton channel.
    e-print [1] Benjamin Fuks, Kaoru Hagiwara, Kai Ma, Ya-Juan Zheng, Phys. Rev. D 104, 034023 (2021) [arXiv:2102.11281 [hep-ph]]
  • November 12, 2021
    Speaker: Kento Asai (Saitama Univ.)
    Title New physics searches at the ILC positron and electron beam dumps
    Abstract We study capability of the ILC beam dump experiment to search for new physics, comparing the performance of the electron and positron beam dumps. The dark photon, axion-like particles, and light scalar bosons are considered as new physics scenarios, where all the important production mechanisms are included: electron- positron pair-annihilation, Primakoff process, and bremsstrahlung productions. We find that the ILC beam dump experiment has higher sensitivity than past beam dump experiments, with the positron beam dump having slightly better performance for new physics particles which are produced by the electron-positron pair-annihilation.
  • November 19, 2021
    Speaker: Kai Murai (Tokyo Univ.)
    Title Big Bang Nucleosynthesis constraints on sterile neutrino and lepton asymmetry of the Universe
    Abstract We consider the cosmological effects of sterile neutrinos with the masses of 150–450 MeV. The decay of sterile neutrinos changes the thermal history of the Universe and affects the energy density of radiation at recombination and the big bang nucleosynthesis (BBN) results. We derive severe constraints on the parameters of sterile neutrinos from the primordial abundances of helium-4 and deuterium. We also find that in a particular model the constraints can be considerably relaxed by assuming a large lepton asymmetry in the active neutrinos. In this case, the consistent parameters result in Neff ≃ 3.2–3.4 and can alleviate the Hubble tension.
    e-print [1] Graciela B. Gelmini, Masahiro Kawasaki, Alexander Kusenko, Kai Murai, Volodymyr Takhistov, JCAP09(2020)051 [arXiv:2005.06721 [hep-ph]]
  • November 26, 2021
    Speaker: Yuji Takai (Hokkaido Univ.)
    Title Semi-Riemannian manifold and number of time-directions
    Speaker: Kentarou Mawatari (Iwate Univ.)
    Title Recent progress in simulation of collider physics
    Abstract I report recent progress in simulation of collider physics, especially in the FeynRules/MadGraph framework.
    e-print [1] S. Frixione, B. Fuks, V. Hirschi, K. Mawatari, H. Shao, P. Sunder, M. Zaro, JHEP 1912 (2019) 008 [arXiv:1907.04898 [hep-ph]]
    [2] SK. Hagiwara, J. Kanzaki, K. Mawatari, Eur.Phys.J.C 80 (2020) 584 [arXiv:2003.03003 [hep-ph]]





    December
  • December 3, 2021
    Speaker: Shohei Takada
    Title Three-generation models from superstring theory
    Speaker: Jun'ya Kume (Tokyo Univ.,RESCEU and Tokyo Univ.)
    Title Phenomenology of chiral gravitational anomaly; Gravitational Leptogenesis and Chiral Gravitational Effect
    Abstract Chiral gravitational anomaly, which exists within the standard model and general relativity, predicts non-trivial interplay between fermions and gravitational waves. In this talk, I introduce two phenomena in the early universe that are the consequence of this anomaly. The first one is so-called "Gravitational Leptogenesis" where primordial lepton asymmetry, which might be the origin of the observed baryon asymmetry, is produced in models of inflation generating helical primordial gravitational waves. I show the difficulties in the minimal model of GL and briefly discuss the extended models where the gauge fields are involved. The other one is "Chiral Gravitational Effect"(CGE), which takes place in the primordial plasma with chiral asymmetry. Note that such an asymmetry can be generated in well-motivated scenarios like GUT baryogenesis, axion inflation. I present how CGE modifies the dynamics of primordial gravitational waves propagating in the chiral plasma.
    e-print [1] K. Kamada, J. Kume, Y. Yamada and J. Yokoyama, JCAP 01 (2020) 016
    [2] K. Kamada, J. Kume and Y. Yamada, JCAP 10 (2020) 030
    [3] K. Kamada, J. Kume and Y. Yamada, JHEP 05 (2021) 292
  • December 10, 2021
    Speaker: Hisakazu Minakata (Tokyo Metropolitan Univ.)
    Title Sterile neutrino, non-unitarity etc. what is next?
    Abstract Sterile neutrinoが見つかったといわれてもう２０年になります。 追試にあたる実験もいろいろ行われましたが、なお決着せず、現在に至っています。最近も少し動きがありました。 この現状を短く紹介するとともに、もう少し広い視野でこれを捉え、ないし関連の現象を混合行列のユニタリー性の破れとして議論するアプローチについてお話します。文献上ではformalismでもまだ統一見解がないように見え、まだまだ未開の分野です。破れの原因が高いあるいは低いスケールにあるのか、標準模型の位相と破れの物理の位相の相関などについてなどについて紹介します。
    e-print [1] Chee Sheng Fong, Hisakazu Minakata, Hiroshi Nunokawa, [arXiv:1609.08623 [hep-ph]]
    [2] Chee Sheng Fong, Hisakazu Minakata, Hiroshi Nunokawa, [arXiv:1712.02798 [hep-ph]]
    [3] Ivan Martinez-Soler, Hisakazu Minakata, [arXiv:1806.10152 [hep-ph]]
    [4] Ivan Martinez-Soler, Hisakazu Minakata, [arXiv:1908.04855 [hep-ph]]
  • December 17, 2021
    Speaker: C.S. Lim (Tokyo Women's Christian Univ.)
    Title The strong CP problem and higher dimensional gauge theories
    Speaker: Ibuki Yamamoto (Hokkaido Univ.)
    Title Black Hole’s mechanics and Information Paradox





    January
  • January 8, 2022
    Speaker: Akihiko Jo(Hokkaido Univ.)
    Title Supersymmetric Gauge Theory on the Graph and Localization
    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]]
  • January 15, 2022
    Speaker: Akihiko Jo(Hokkaido Univ.)
    Title Supersymmetric Gauge Theory on the Graph and Localization
    Speaker: Masaki Honda (Waseda Univ.)
    Title Electroweak Axion String and Superconductivity
    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 22/29, 2022
    Master thesis presentation (long/short)
    Speaker: Shota Kikuchi (Hokkaido Univ.)
    Title Classification of three generation models by orbifolding magnetized $T^2 ¥times T^2$