2021年度のセミナー

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(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.

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.

 

過去のセミナー