2021年度のセミナー

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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