Seminar - Particle Physics Theory Group

2021年度のセミナー

Date/Place	February 1st (Tue.) 15:40-16:40 / Online
Name	Kantaro Ohmori (Tokyo U.) (Slides)
Title	非可逆的対称性とその応用を目指して
Abstract	本講演では非可逆的対称性と呼ばれる、対称性の局所的理論における一般化について、前半部分では(1+1次元における)その量子情報的定式化を、後半部分では高次元への一般化と、知られている具体例について、概説したい。

Date/Place	January 25th (Tue.) 15:40-16:40 / Hybrid
Name	Yuta Nagoya (Osaka U.)
Title	Non-invertible topological defects in 4-dimensional ℤ2 pure lattice gauge theory
Abstract	In recent years, the extension of the concept of symmetry has been actively studied. One of the directions is “non-invertible symmetry’’, in which the set of non-invertible topological defects is regarded as “symmetry’’. In 2-dimensions, there are active studies of non-invertible symmetry, and there are many examples and applications. On the other hand, non-invertible symmetries in higher dimensions are less understood than those in 2-dimensions. In this talk, we will explore non-invertible topological defects in the 4-dimensional Z2 pure lattice gauge theory. This theory has 1-form Z2 center symmetry as well as the Kramers-Wannier-Wegner (KWW) duality. We construct topological defects associated with them in a similar way to those constructed by Aasen, Mong, and Fendly for the 2-dimensional Ising model. The KWW duality defect turns out to be non-invertible. The crossing relations among these defects are derived. This talk is based on the paper [arXiv: 2109.05992].

Date/Place	January 18th (Tue.) 15:40-16:40 / Hybrid
Name	Kazuki Sakurai (Warsaw U.) (Slides)
Title	SUSY solution to the (g-2)_mu anomaly with and without stable neutralino.
Abstract	Supersymmetry is an attractive new physics candidate that may explain the observed anomaly in the muon g-2. In the MSSM, this requires either (a) large higgsino-gaugino mixing, or (b) large L-R mixing in the smuon sector. Both cases are strongly constrained if the lightest neutralino is the dark matter. For example, the former case is severely constrained by the direct detection measurements, while the latter case suffers from overproduction of the Bino-like neutralino. We will first show how those constrains restrict the parameter space favoured by the muon g-2. In the second part of the talk, we study two scenarios where the neutralino is not the dark matter; (1) RPV and (2) GMSB with the gravitino LSP. We carefully study the collider constraints on these scenarios and show how they can open up the parameter regions favoured by the muon g-2, otherwise excluded in the MSSM with neutralino dark matter.

Date/Place	January 11th (Tue.) 15:40-16:40 / Hybrid
Name	Ryosuke Sato (Osaka U.)
Title	Axion fragmentation
Abstract	Axion (およびaxion like particle) は素粒子模型にしばしばあらわれる、周期的ポテンシャルを持つ軽い擬スカラー粒子である。 Axionの一様成分が初期宇宙などで十分大きな運動エネルギーを持っていた場合、一様成分が一定の速度を保ちポテンシャルを乗り越え転がり続けることができる。この過程において、一種の共鳴現象が起きることにより、Axionの空間的な揺らぎが指数関数的に成長し、axionの一様成分から運動エネルギーを奪うことができる。本講演では、この現象を"axion fragmentation"と呼び、摂動的な解析計算と非摂動的な数値計算の２つの手法により議論する。

Date/Place	December 21th (Tue.) 15:40-16:40 / Online
Name	Kai Murai (ICRR, Tokyo U.) (Slides)
Title	SU(N)-natural inflation
Abstract	We study SU(N) gauge fields that couple to the inflaton through the Chern-Simons term. In this talk, I will shortly review the dynamics of SU(2) gauge fields during inflation and provide a general procedure to construct homogeneous, isotropic, and attractor solutions of SU(N) gauge fields during inflation. As specific examples, we construct the stable solutions for N=3 and 4 and numerically confirm that they are complete and attractor. I will also discuss the generation of primordial gravitational waves in our model. It is straightforward to apply our procedure to the other simple Lie groups. This talk is based on the paper [arXiv: 2110.03228].

Date/Place	December 14th (Tue.) 15:40-16:40 / Hybrid
Name	Takuya Yoda (Kyoto U.)
Title	New perspective for the APS index theorem
Abstract	Recently, the APS index has been reformulated as the eta invariant of the Dirac operators with a domain wall mass which plays a key role in the anomaly inflow of the topological insulator with boundary. In this talk, we will provide conjectures (and justifications) that the reformulated version of the APS index is given simply from the Berry phase associated with domain wall Dirac operators, and from the Witten index of a supersymmetric quantum mechanics. These will open up a new perspective that the anomaly inflow is ``the limit'' of a more general struture of QFT.

Date/Place	December 7th (Tue.) 9:00-10:00 / Online
Name	Takemichi Okui (KEK)
Title	Primordial black holes from bubble collisions during a first-order phase transition
Abstract	I will talk about how collisions of true vacuum bubbles during a first-order phase transition can produce a sizable abundance of primordial black holes (PBHs), provided that bubble walls have a non-negligible thickness and the transition lasts long enough. An approximately monochromatic PBH mass spectrum is expected, and the PBHs can constitute the whole dark matter with their masses in the currently allowed range of 10^(-15) ~ 10^(-11) solar masses if the phase transition occurs around 10^5 -~ 10^7 GeV. Combining this result with bounds on the PBH abundance can constrain models with a first-order phase transition.

Date/Place	November 30th (Tue.) 15:40-16:40 / Online
Name	Wen Yin (Tohoku U.) (Slides)
Title	CP-violating light dark sector
Abstract	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.

Date/Place	November 16th (Tue.) 15:40-16:40 / Hybrid
Name	Nagisa Hiroshima (Toyama U.) (Slides)
Title	Indirect search of dark matter from multiple aspects
Abstract	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.

Date/Place	November 9th (Tue.) 15:40-16:40 / Online
Name	Kanato Goto (RIKEN) (Slides)
Title	Islands and Cosmology
Abstract	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.

Date/Place	November 2nd (Tue.) 15:40-16:40 / Hybrid
Name	Kenta Suzuki (YITP) (Slides)
Title	Bi-local Holography of the SYK Model
Abstract	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.

Date/Place	October 26th (Tue.) 15:40-16:40 / Online
Name	Yuto Minami (RCNP) (Slides)
Title	A new measurement of the cosmic birefringence
Abstract	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.

Date/Place	October 19th (Tue.) 15:40-16:40 / Online
Name	Yoshimasa Hidaka (KEK) (Slides)
Title	Generalized global symmetry and application to Spontaneous symmetry breaking and QCD phase diagram
Abstract	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.

Date/Place	October 12th (Tue.) 15:40-16:40 / Online
Name	Yuya Tanizaki (YITP) (Slides)
Title	Non-invertible symmetry and string tensions beyond N-ality
Abstract	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.

Date/Place	Oct. 5th (Tue.) 15:40-16:40 / Online
Name	Ryuichiro Kitano-san (KEK) (Slides)
Title	Stochastic computation of g−2 in QED
Abstract	We perform a numerical computation of the anomalous magnetic moment (g−2) of the electron in QED by using the stochastic perturbation theory. Formulating QED on the lattice, we develop a method to calculate the coefficients of the perturbative series of g−2 without the use of the Feynman diagrams. We demonstrate the feasibility of the method by performing a computation up to the alpha^3 order and compare with the known results. This program provides us with a totally independent check of the results obtained by the Feynman diagrams and will be useful for the estimations of not-yet-calculated higher order values. This work provides an example of the application of the numerical stochastic perturbation theory to physical quantities, for which the external states have to be taken on-shell.

Date/Place	July 27th (Tue.) 15:40-16:40 / Online
Name	Sotaro Sugishita-san (Nagoya U.) (Slides)
Title	Target space entanglement in quantum mechanics of fermions and matrices
Abstract	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.

Date/Place	July 20th (Tue.) 15:40-16:40 / Online
Name	Yoshiyuki Matsuki-san (Osaka U.) (Slides)
Title	Fractal defect states in the Hofstadter butterfly
Abstract	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].

Date/Place	July 13th (Tue.) 15:40-16:40 / Online
Name	Hitoshi Murayama-san (UC Berkeley) (Slides)
Title	Some Exact Results in QCD-like and Chiral Gauge Theories
Abstract	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.

Date/Place	July 6th (Tue.) 15:40-16:40 / Online
Name	Ryutaro Matsudo-san (KEK) (Slides)
Title	Vector mesons on η' domain walls
Abstract	We show that, in the effective theory for pions and η', there needs to be a dynamical domain wall on which a U(N_f)_{-N_c} 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(N_f)_{-N_c} 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 N_c/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.

Date/Place	June 29th (Tue.) 15:40-16:40 / Online
Name	Arindam Das (Hokkaido U.)
Title	Probing the minimal U(1)X model at future electron-positron collider via the fermion pair production channel
Abstract	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

Date/Place	June 25th (Fri.) 15:30-16:30 / Online
Name	Kazunori Kohri-san (KEK)
Title	Primordial black holes and particle physics
Abstract	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]).

Date/Place	June 15th (Tue.) 15:40-16:40 / Online
Name	Hayato Kanno-san (YITP)
Title	Anomaly and Superconnection (Slides)
Abstract	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].

Date/Place	June 8th (Tue.) 15:40-16:40 / Online
Name	Yasuhito Sakaki-san (KEK)
Title	Fixed target experiments using electron and positron beams (Slides)
Abstract	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.

Date/Place	June 1st (Tue.) 15:40-16:40 / Online
Name	Masaki Shigemori (Nagoya University)
Title	TT Deformation of stress-tensor correlators from random geometry (Slides)
Abstract	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.

Date/Place	May 25th (Tue.) 15:40-16:40 / Online
Name	Yoshiki Uchida-san (Kyushu University)
Title	Formulation of new normal coordinate system in generalized HEFT (Slides)
Abstract	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.

Date/Place	May 18th (Tue.) 15:40-16:40 / Online
Name	Hiroshi Suzuki-san (Kyushu University)
Title	Gradient flow exact renormalization group (Slides)
Abstract	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.

Date/Place	May 11th (Tue.) 15:40-16:40 / Online
Name	Taisuke Katayose-san (Osaka U.)
Title	The search for majorana fermionic dark matter at collider
Abstract	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.

Date/Place	April 27th (Tue.) 15:40-16:40 / Online
Name	Michihisa Takeuchi-san (Osaka U.)
Title	New Physics searches at the LHC and beyond
Abstract	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.

Date/Place	April 20th (Tue.) 15:40-16:40 / Online
Name	Okuto Morikawa-san (Osaka U.)
Title	Perturbative ambiguities and resurgence in compactified spacetime (Slides)
Abstract	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.

Date/Place	April 13th (Tue.) 15:40-16:40 / Online
Name	Ryo Nagai-san (Osaka U.)
Title	On-shell amplitudes in generalized HEFT (Slides)
Abstract	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.

2020年度のセミナー

Date/Place	January 26th (Tue.) 15:30-16:30 / Online
Name	Kazuki Sakurai (Warsaw U.)
Title	On the phenomenology of sphaleron-induced processes at the LHC and beyond (Slides)
Abstract	In this talk, I will discuss experimental signatures of the sphaleron/instanton-induced processes in the electroweak theory. First I will briefly review what are the sphalerons and instantons in the electroweak theory, and discuss their signatures and some studies on their cross-sections. Although many studies suggest such processes have unobservably small cross-sections, some suggest otherwise. “IF" EW sphaleron processes occur at the LHC or other experiments, what signature do we expect? How can we set a bound on the theoretical calculation? How can we simulate those processes? I will address those questions in this talk.

Date/Place	January 19th (Tue.) 10:30-11:30 / Online
Name	Xizhi Han-san (Stanford U.)
Title	Neural Network Variational Ansatz for Matrix Quantum Mechanics (Slides)
Abstract	We employ machine learning techniques to provide accurate variational wavefunctions for matrix quantum mechanics, with multiple bosonic and fermionic matrices. Variational quantum Monte Carlo is implemented with deep generative flows to search for gauge invariant low energy states. The ground state, and also long-lived metastable states, of an SU(N) matrix quantum mechanics with three bosonic matrices, as well as its supersymmetric `mini-BMN' extension, are studied as a function of coupling and N. Known semiclassical fuzzy sphere states are recovered, and the collapse of these geometries in more strongly quantum regimes is probed using the variational wavefunction. We then describe a factorization of the quantum mechanical Hilbert space that corresponds to a spatial partition of the emergent geometry. Under this partition, the fuzzy sphere states show a boundary-law entanglement entropy in the large N limit.

Date/Place	January 12th (Tue.) 15:30-16:30 / Online
Name	Kazunori Nakayama (Tokyo U.)
Title	Constraint on Vector Coherent Oscillation Dark Matter
Abstract	Light vector boson (or hidden photon) is a well-motivated dark matter candidate. There are several proposed mechanisms to produce such vector dark matter. In this talk I focus on the coherent oscillation scenario of the vector boson. I first review some historical aspects of this scenario and introduce models that would predict vector coherent oscillation as dark matter. All the known models suffer from theoretical inconsistency or severe observational constraints.

Date/Place	January 5th (Tue.) 15:30-16:30 / Online
Name	Yuya Tanizaki (Kyoto U.)
Title	Topological aspects of oblique confinement in the Cardy-Rabinovici model
Abstract	Confinement is one of the most important but basic features of non-Abelian gauge theories, and an intuitive and interesting scenario of its dynamics is condensation of magnetic monopoles. When we add the topological theta term to it, more exotic condensations may appear, which are called oblique confinement phases. In a 4d lattice model proposed by Cardy and Rabinovici, such interesting phases can be explicitly realized. In this talk, I will uncover its topological nature based on the recent applications of 't Hooft anomaly matching. Moreover, it has been known that the local dynamics of Cardy-Rabinovici model shows the SL(2,Z) self-duality, but it turns out that the self-duality does not extend to the global aspect of the original theory. We cooked up a SL(2,Z) self-dual theory by gauging a part of the 1-form symmetry of the Cardy-Rabinovici model, and the self-duality has a mixed gravitational anomaly. These data give useful constraints to discuss the phase diagram.

　

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