[ 素粒子論セミナー ]

講演者

Wen Yin (Tohoku U.)

日時

2021年11月30日(火)15:40-16:40

場所

Online

概要

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Recently, a light dark sector is popularly studied in the context of e.g. dark matter. A CP symmetry in the dark sector is usually assumed despite that it is absent in the standard model, and despite that the CP-conservation nature in QCD is dubbed as a problem. I will talk about the possibility the dark sector is CP-violating. In particular, I will discuss the following: 1. A simple dark Higgs model with CP-violation predicts a CP even axion-like particle (ALP). Then I discuss its phenomenology and cosmology. This is based on 2111.03653. 2. In the context of axiverse, a light ALP can mediate a long range force from the dark matter in the CP-violating dark sector to induce a spin precession of SM fermions on Earth. Interestingly, the cosmic axion force is toward the galaxy center. Measuring the daily modulation of the precession can probe the axionic force. This part is based on 2105.03422.

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[ 素粒子論セミナー ]

Indirect search of dark matter from multiple aspects

講演者

Nagisa Hiroshima (Toyama U.)

日時

2021年11月16日(火)15:40-16:40

場所

Hybrid

概要

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Dark matter (DM) is a mysterious component of our Universe that occupies ~25% of the total energy density. Among the numbers of candidates, weakly interacting massive particle (WIMP) has the one most intensively studied. The signatures or imprints of DM, such as those of WIMP, take many forms in astrophysical and cosmological observables. In this talk, I introduce WIMP search focusing on gamma-ray observation and its connection to the property of DM halo.

[ 物性物理学セミナー ]

ミュオンビームによる高温超伝導物質の研究−銅酸化物と鉄カルコゲナイド、将来は水素化物−

講演者

足立匡 教授(上智大学理工学部)

日時

2021年11月16日(火) 15:10から(4限)

場所

理学研究科D303

概要

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 ミュオンは、物質中の微視的な磁性を調べられるだけでなく、イオンの拡散をプローブできる、水素のシミュレーターとしても利用できることから、磁性材料、超伝導材料から電池材料、水素材料など幅広い分野で利用されている。本セミナーでは、ミュオンの幅広い用途について簡単に紹介した後に、我々が行ってきたミュオンスピン緩和(muSR)測定による高温超伝導物質のスピンダイナミクスの研究を2つ紹介する。
1. 電子ドープ型銅酸化物におけるノンドープ超伝導の研究。ミュオンだけでなく、中性子、放射光も相補利用してわかってきた母物質で発現するノンドープ超伝導のメカニズムについて議論する。
2. 鉄カルコゲナイド薄膜における磁性、超伝導、電子ネマティシティの関連の研究。低エネルギーミュオンを用いた測定から高濃度にSを置換した FeSe1-xSxにおいて新奇な磁性を観測した。この磁性と超伝導、電子ネマティック状態の関連について議論する。
 最後に、今後のmuSRによる研究として界面超伝導と水素化物超伝導についての展望を話したい。

[ 素粒子論セミナー ]

Islands and Cosmology

講演者

Kanato Goto (RIKEN)

日時

2021年11月9日(火)15:40-16:40

場所

Online

概要

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In recent research developments in the black hole information paradox, it was found that the quantum extremal islands reproduce the unitary Page curve of an evaporating black hole. The existence of the island suggests that information in quantum gravity is stored in a non-local form. This mechanism is crucial not only in the case of the late stage of the black hole evaporation, but also in similar situations wherein a large amount of information is contained in a tiny spacetime region, such as the early universe. In this talk, I will give an overview of the recent developments in the islands and its application to cosmology.

[ 素粒子論セミナー ]

Bi-local Holography of the SYK Model

講演者

Kenta Suzuki (YITP)

日時

2021年11月2日(火)15:40-16:40

場所

Online

概要

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The Sachdev-Ye-Kitaev (SYK) model is a quantum mechanical many-body system with random all-to-all interactions on fermionic N sites (N>>1). This model is known to saturate the maximal chaos bound of many-body system and then based on this observation it is conjectured to be dual to a quantum black hole in the sense of the AdS/CFT correspondence.
In this talk, we start from reviewing basis aspects of the SYK model in the large N limit, which is systematically described by a single bi- local collective field. We show that a propagator of the bi-local field, which is understood as a four-point function of the original fermions, predicts the spectrum of the dual AdS_2 theory, but it has a divergent contribution from the zero mode at the critical IR fixed point of the model. We also discuss the derivation of the Schwarzian action which is the effective action describes the zero mode dynamics.
Finally, we also introduce a partially disorder-averaged SYK model, by modifying the probability distribution of the random coupling constant. We show that this model smoothly interpolates between the ordinary total disorder-averaged SYK model and the totally fixed-coupling model. For the large N effective description, in addition to the usual bi-local collective fields, we also introduce a new additional set of local collective fields. These local fields can be understood as the ''half'' of the bi-local collective fields, and we study implications of these new local collective fields.

[ 素粒子論セミナー ]

A new measurement of the cosmic birefringence

講演者

Yuto Minami (RCNP)

日時

2021年10月26日(火)15:40-16:40

場所

Online

概要

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Polarised light of the cosmic microwave background, the remnant light of the Big Bang, is sensitive to parity-violating physics, cosmic birefringence. In this presentation we report on a new measurement of cosmic birefringence from polarisation data of the European Space Agency (ESA)’s Planck satellite. The statistical significance of the measured signal is 2.4 sigma. If confirmed with higher statistical significance in future, it would have important implications for the elusive nature of dark matter and dark energy.

[ 素粒子論セミナー ]

Generalized global symmetry and application to Spontaneous symmetry breaking and QCD phase diagram

講演者

Yoshimasa Hidaka (KEK)

日時

2021年10月19日(火)15:40-16:40

場所

Online

概要

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An ordinary symmetry is a symmetry acting on a point particle. This concept can be generalized to symmetry acting on extended objects. Such symmetry is called higher form symmetry. In this talk, we discuss spontaneous breaking of higher form symmetries in a nonrelativistic system and show the counting rule of the Nambu-Goldstone modes. We also discuss an application of higher-form symmetries to the QCD phase diagram and discuss the possibility of quantum phase transition in a dense QCD.

[ 素粒子論セミナー ]

Non-invertible symmetry and string tensions beyond N-ality

講演者

Yuya Tanizaki (YITP)

日時

2021年10月12日(火)15:40-16:40

場所

Online

概要

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String tension is one of the characteristic quantity in confining gauge theories. In SU(N) gauge theories, there is a center symmetry, or Z_N 1-form symmetry, which acts on the test quarks, and this is the symmetry which controls the spectral properties of confining strings in the infrared regime. This is sometimes called as an N-ality rule. In this talk, I will construct a simple toy model, which we call the 3d semi-Abelian gauge theory, and the N-ality rule is violated there. That is, the center symmetry is again given by Z_N as in the case of SU(N) theory, while the confining strings of Wilson loops carry detailed information on their representations beyond N-ality. Then, I will uncover that our model enjoys the non-invertible symmetry, and they can naturally explain why the N-ality rule is violated. I will also comment on the observation that the exactly same story is true for 2d pure Yang-Mills theory.

[ 素粒子論セミナー ]

Target space entanglement in quantum mechanics of fermions and matrices

講演者

Sotaro Sugishita (Nagoya U.)

日時

2021年7月27日(火)15:40-16:40

場所

Online

概要

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I will introduce the notion of target space entanglement. Quantum entanglement is closely related to the structure of spacetime in quantum gravity. For quantum field theories or statistical models, we usually consider the base space entanglement. However, target space instead of base space sometimes directly connects to our spacetime, for example, perturbative string theories. We thus need target space entanglement. To define the target space entanglement, we have to generalize the definition of the conventional entanglement entropy. I will explain this generalization and apply it to the first quantized particles, in particular, fermions.

[ 素粒子論セミナー ]

Fractal defect states in the Hofstadter butterfly

講演者

Yoshiyuki Matsuki (Osaka U.)

日時

2021年7月20日(火)15:40-16:40

場所

Online

概要

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We investigate the electronic properties in the Bloch electron on a two-dimensional lattice with vacancies in the uniform magnetic field. We show that a single vacancy site introduced to the system creates a defect energy level in every single innumerable fractal energy gap in the Hofstadter butterfly. The wavefunctions of different defect levels have all different localization lengths depending on their fractal generations, and they can be described by a single universal function after an appropriate fractal scaling. We also show that each defect state has its own characteristic orbital magnetic moment, which is exactly correlated to the gradient of the energy level in the Hofstadter diagram. Probing the spatial nature of the defect-localized states provides a powerful way to elucidate the fractal nature of the Hofstadter butterfly [arXiv:2102.12153].

[ 物性物理学セミナー ]

Nonequilibrium superconductivity toward a realization at high temperature

講演者

Professor Naoto Tsuji
(Department of Physics, The University of Tokyo )

日時

Tuesday July 13, 17:30-

場所

Online

概要

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Realizing superconductivity at high temperature is one of long-standing goals in physics, and has stimulated various developments in condensed matter physics. Apart from conventional approaches to superconductivity in equilibrium, there has recently emerged a new approach to realize superconductivity out of equilibrium. At first sight, such an idea would not work since superconducting coherence might be destroyed at high energies. However, contrary to our intuition, it is known that there exists a high-energy nonequilibrium state that shows superconductivity. If one can find a way to access such a state, superconductivity is expected to emerge from a high-temperature initial state. In this talk, I will review recent developments of nonequilibrium superconductivity including our attempt.
--------
IPC intensive lecture will be given online by Prof. Naoto Tsuji of Univ. of Tokyo during 7/12-14. He has also kindly agreed to give an online seminar talk, so you are welcome to participate.
問い合わせ先:黒木 和彦 (理学研究科物理学専攻)

[ 素粒子論セミナー ]

Some Exact Results in QCD-like and Chiral Gauge Theories

講演者

Hitoshi Murayama (UC Berkeley)

日時

2021年7月13日(火)15:40-16:40

場所

Online

概要

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I present some exact results in QCD-like and chiral gauge theories. They are exact when supersymmetric gauge theories are perturbed by anomaly-mediated supersymmetry breaking (AMSB). Thanks to the UV-insensitivity of AMSB, SUSY results can be perturbed with no ambiguities even when applied to composite fields. I find two phases for QCD-like theories, one with chiral symmetry breaking and another conformal. To best of my knowledge, this is the first analytic derivation of chiral symmetry breaking in QCD for SU(3) and Nf=2 or 3. Our results for chiral gauge theories do not agree with what had been suggested by tumbling. We suggest alternative schemes of tumbling-like interpretations. We see no evidence that large SUSY breaking leads to phase transitions, perhaps protected by holomorphy. I also present a few examples of our predictions which I hope will be tested by lattice QCD.

[ 素粒子論セミナー ]

Vector mesons on η' domain walls

講演者

Ryutaro Matsudo (KEK)

日時

2021年7月6日(火)15:40-16:40

場所

Online

概要

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We show that, in the effective theory for pions and η', there needs to be a dynamical domain wall on which a U(Nf)-Nc Chern-Simons theory is supported by taking into account a mixed anomaly involving the θ-periodicity and the global symmetry. When the domain wall has a boundary, we conclude that there should be a boundary term that couples the U(Nf)-Nc gauge field to the vector mesons. We also confirm that the recent proposal that the domain wall bounded by the string describes the baryon with spin Nc/2 by determining the coupling of the background gauge fields to the wall. We discuss the impact on physics of the chiral phase transition and the relation to the "duality" of QCD. This talk is based on the paper arXiv:2011.14637.

[ 素粒子論セミナー ]

Probing the minimal U(1)X model at future electron-positron collider via the fermion pair production channel

講演者

Arindam Das (Hokkaido U.)

日時

2021年6月29日(火)15:40-16:40

場所

Online

概要

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The general U(1)𝑋 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, 𝑍′ which interacts with the SM and BSM particles showing a variety of new physics driven signatures. After the anomaly cancellation the U(1)𝑋 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 𝑍′. In this paper we investigate the pair production mechanism of the different charged through the photon, 𝑍 and 𝑍′ boson exchange processes at the electron-positron (𝑒−𝑒+). The angular distributions, forward-backward (A_FB), left-right (A_LR) and left-right forward-backward (A_LR,FB) asymmetries of the different charged fermion pair productions show substantial deviation from the SM results. Reference: arXiv:2104.10902

[ 素粒子論セミナー ]

Primordial black holes and particle physics

講演者

Kazunori Kohri (KEK)

日時

2021年6月25日(金)15:30-16:30

場所

Online

概要

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After aLIGO detected the gravitational wave (GW) produced by mergers of binary black holes (BHs), researchers have aggressively studied the origin of the BHs with masses of the order of O(10) M_sun. In addition to astrophysical origins through evolutions of Pop.III/Pop.II stars, one of the attractive candidates of those BHs should be Primordial Black Holes (PBHs). The PBHs can be produced in the early radiation and matter dominated Universe due to spherical collapses of regions which have a large curvature perturbation produced by inflation. I will explain the mechanism of the PBH formations in the early Universe in detail. Next, I will review the current status of cosmological and astrophysical constraints on PBHs with introducing my own latest bounds on PBHs in terms of polarization of Cosmic Microwave Background photons due to cosmological accretions onto PBHs (arXiv:1707.04206 [astro-ph.CO], arXiv:2002.10771 [astro-ph.CO]), CMB distortions (arXiv:1405.5999 [astro-ph.CO]), gamma-ray/cosmic-rays/BBN bounds on evaporating PBHs (arXiv:0912.5297 [astro-ph.CO], arXiv:2002.12778 [astro-ph.CO]), Higgs phenomenology (arXiv:1708.02138 [hep-ph]), stochastic GWs (arXiv:1903.05924 [astro-ph.CO], arXiv:1904.12879 [astro-ph.CO], arXiv:2009.11853 [astro-ph.CO]), PBH dark matter (arXiv:1802.06785 [astro-ph.CO]), ultra-compact mini halo formations (arXiv:1905.04477 [astro-ph.CO]] and so on. If time permitted, I will mention the current status of concrete inflation modes based on particle physics which can successfully produce PBHs (e.g., arXiv:0711.5006 [hep-ph], arXiv:0906.1398 [astro-ph.CO], arXiv:1211.2371 [hep-ph]).

[ 素粒子論セミナー ]

Anomaly and Superconnection

講演者

Hayato Kanno (YITP)

日時

2021年6月15日(火)15:40-16:40

場所

Online

概要

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We study anomalies of fermion with spacetime dependent mass. We calculate anomalies, which associate with the U(N)×U(N) chiral symmetry for even dimension and U(N) flavor symmetry for odd dimension, using Fujikawa method. These anomalies can be written by superconnection. In particular, we focus on vector-like U(1) part of the anomalies. These results can be applied to some general systems with interfaces and boundaries. They are also useful to some index theorems, such as APS index theorem. In the last part of this talk, the relation between this anomaly and string theory is discussed. This talk is based on [arXiv:2106.01591].

[ 素粒子論セミナー ]

Fixed target experiments using electron and positron beams

講演者

Yasuhito Sakaki (KEK)

日時

2021年6月8日(火)15:40-16:40

場所

Online

概要

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Now that new heavy particles have not been found at the LHC, focusing on light and weakly interacting new particles is one direction to go. Fixed target experiments using accelerators play a part in this. I will explain the basics of the phenomena in fixed target experiments, and how to calculate the number of signal on a target induced by e+ e- beams. Trends in some fixed-target experiments will be introduced. I will discuss some ideas for fixed target experiments at the ILC and KEK.

[ 素粒子論セミナー ]

TT Deformation of stress-tensor correlators from random geometry

講演者

Masaki Shigemori (Nagoya University)

日時

2021年6月1日(火)15:40-16:40

場所

Online

概要

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We study stress-tensor correlators in the TTbar-deformed conformal field theories in two dimensions. Using the random geometry approach to the TTbar deformation, we develop a geometrical method to compute stress-tensor correlators. More specifically, we derive the TTbar deformation to the Polyakov-Liouville conformal anomaly action and calculate three and four-point correlators to the first-order in the TTbar deformation from the deformed Polyakov-Liouville action. The results are checked against the standard conformal perturbation theory computation and we further check consistency with the TTbar-deformed operator product expansions of the stress tensor. A salient feature of the TTbar-deformed stress-tensor correlators is a logarithmic correction that is absent in two and three-point functions but starts appearing in a four-point function.

[ 素粒子論セミナー ]

Formulation of new normal coordinate system in generalized HEFT

講演者

Yoshiki Uchida (Kyushu University)

日時

2021年5月25日(火)15:40-16:40

場所

Online

概要

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The HEFT is the most general effective field theory with non-linearly realized electroweak symmetry, but it cannot treat the production or decay processes of new particles. In the previous work, we extend the HEFT so that it includes the arbitrary number of neutral and charged scalar fields. In some of the BSM models such as non-minimal composite Higgs models, however, the SM fermion partners are predicted in addition to the new scalar matter fields, and in order to treat these additional fermions in a consistent manner, we have to extend the HEFT so that it includes not only new scalars but also these new fermion fields. In the recent work, we formulate the generalized HEFT including new fermion fields as well as new scalar fields. The physical observables should not depend on the choice of the field basis, so they should be expressed in terms of covariant quantities under the field transformations. In the non-linear sigma models, there is a useful coordinate called Riemann Normal Coordinate (RNC), where the Taylor expansion coefficients are expressed in terms of covariant quantities. Thanks to its systematic expansion, the RNC enables us to evaluate the multi-point amplitude easily. In the general system with fermion fields, however, there is no such coordinate system. In this talk, I will extend the RNC and introduce a new coordinate system that can be applied to the general theory including fermion fields.

[ 素粒子論セミナー ]

Gradient flow exact renormalization group

講演者

Taisuke Hiroshi Suzuki (Kyushu University)

日時

2021年5月18日(火)15:40-16:40

場所

Online

概要

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The so-called gradient flow, a gauge covariant diffusion of the gauge field, bears a close resemblance to the coarse graining involved in the Wilsonian renormalization group (RG). In scalar field theory, a precise connection between the gradient flow and the Wilsonian RG flow can be made. By imitating the structure of this connection, we propose a Wilsonian RG equation that preserves manifest gauge invariance in vector-like gauge theory. I also mention some ongoing studies on the basis of this formulation.

[ 素粒子論セミナー ]

The search for majorana fermionic dark matter at colliderHC and beyond

講演者

Taisuke Katayose (Osaka U.)

日時

2021年5月11日(火)15:40-16:40

場所

Online

概要

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It is known that direct detection experiments put the severe constraint on WIMPs at electroweak scale. We discuss the some exceptional cases where WIMPs are difficult to detect, focusing on majorana fermionic WIMPs and collider signals. We studied such dark matters using effective field theory, and it enable us to discuss WIMPs model independently.

[ 素粒子論セミナー ]

New Physics searches at the LHC and beyond

講演者

Michihisa Takeuchi (Osaka U.)

日時

2021年4月27日(火)15:40-16:40

場所

Online

概要

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In particle physics, there is an established model describing all particle interactions we can observe on the earth, the Standard Model. However, it is known that there are several problems in the Standard Model. Among them I am focusing on existence of the dark matter and the hierarchy problem in the Higgs sector. Both problems indicates the existence of new particles around a TeV scale. The Large Hadron Collider is the best place for directly probing such new physics at a TeV scale and its future upgrade options are also discussed. I have been focusing on top partner searches at the LHC, and I developed the state-of-the art top tagging algorithm using jet substructures. I will show the detail of those and also discuss what else we can do and what would be interesting in future.

[ 物性物理学セミナー ]

X線とレーザーの融合による遷移金属化合物のダイナミクス研究

講演者

和達大樹 教授(兵庫県立大学大学院理学研究科)

日時

4月20日(火) 16:50~

場所

理学研究科 D403

概要

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遷移金属化合物は、高温超伝導、巨大磁気抵抗効果、マルチフェロイック性、金属絶縁体転移などの興味深い性質のために、物性物理学において常に注目を集めている。上記の多彩な性質の背景にはほとんどの場合、電荷・スピン・軌道の秩序が起こっており、このような秩序状態を観測することは極めて重要である。本セミナーでは、X線とレーザーの融合による秩序状態とそのダイナミクス研究を紹介する。超短パルスレーザーを組み合わせたポンプ・プローブ型の時間分解測定により、ピコ秒以下のスケールでの格子振動などの格子ダイナミクスや、強磁性体の磁化が消える(消磁)スピンのダイナミクスの観測に成功している。また、大型施設によらず実験室光源でX線を得る試みも進展が大きな分野であり、我々の試みにも言及したい。

問い合わせ先 : 木村 真一(生命機能研究科/理学研究科物理学専攻)

[ 素粒子論セミナー ]

Perturbative ambiguities and resurgence in compactified spacetime

講演者

Okuto Morikawa (Osaka U.)

日時

2021年4月20日(火)15:40-16:40

場所

Online

概要

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In general, perturbation theory possesses intrinsic ambiguities due to divergent behaviors of perturbation series. In the context of the resurgence program, such ambiguities are eventually canceled against ambiguities of nonperturbative calculations. Recently, it was conjectured that the perturbative ambiguity caused by the IR renormalon corresponds to the semi-classical object called a bion. This conjecture requires the S^1 compactification with the Z_N twisted boundary condition, in which the bion solution is found. Contrary to this conjecture, we argue that the bion cancels the perturbative ambiguity caused by the proliferation of Feynman diagrams, which are significantly affected by the compactification. We then find that there is no IR renormalon in the SU(N) gauge theory with adjoint fermions on R^3xS^1. These observations are helpful in giving a unified understanding on the resurgence in QFTs.

[ 素粒子論セミナー ]

On-shell amplitudes in generalized HEFT

講演者

Ryo Nagai (Osaka U.)

日時

2021年4月13日(火)15:30-16:30

場所

Online

概要

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Beyond standard model (BSM) particles should be included in effective field theory in order to compute the scattering amplitudes involving these extra particles. We formulate an extension of Higgs effective field theory (HEFT) which contains arbitrary number of scalar and fermion fields with arbitrary electric and chromoelectric charges. The BSM Higgs sector is described by using the non-linear sigma model in a manner consistent with the spontaneous electroweak symmetry breaking. We use a geometrical language to describe the particle interactions. The parametrization redundancy in the effective Lagrangian is resolved by describing the on-shell scattering amplitudes only with the covariant quantities in the scalar/fermion field space. We introduce a useful coordinate (normal coordinate), which simplifies the computations of the on-shell amplitudes significantly. We show the high energy behaviors of the scattering amplitudes determine the “curvature tensors” in the scalar/fermion field space.

On the phenomenology of sphaleron-induced processes at the LHC and beyond
Speaker: Kazuki Sakurai (Warsaw U.)

2021年1月26日 開催

スクール

高エネルギー物理春の学校

2015年6月10-12日

物理院生春の学校

2015年3月9-11日

ICEPPシンポジウム

2015年2月8-11日