2020年度のセミナー

Date/Place December 22th (Tue.) 16:00-16:45 / Online
Name Eibun Senaha (Ton Duc Thang U.)
　Title　 Electroweak baryogenesis in general 2HDM: update (Slides)
Abstract Baryon asymmetry of the Universe (BAU) is tangible evidence that calls for new physics. After the discovery of the Higgs particle in 2012, much attention has been paid to a scenario based on Higgs physics in which the asymmetry is generated by electroweak phase transition, i.e., electroweak baryogenesis (EWBG). Thanks to experimental efforts such as LHC and ACME, the scenario is now under siege. In this talk, I will begin by going though current status of EWBG, and then discuss our recent work: (1) a sphaleron decoupling condition taking a magnetic mass effect into consideration (2003.13929) and (2) a built-in cancellation mechanism for electron electric dipole moment (1910.12404) in a general 2 Higgs doublet model. It is found that EWBG parameter space in this model is still wide open due to the above effects.

Date/Place December 15th (Tue.) 15:30-16:30 / Online
Name Kotaro Tamaoka (Kyoto Univ.)
　Title　 Pseudo Entropy: A Measure of Quantum Information from Quantum Gravity (Slides)
Abstract Recently, various quantum information-theoretic quantities have been discovered from string theory. In this seminar, we will discuss one of them, called pseudo entropy (PE). In particular, we discuss the following three natures of the PE: (1) the PE is a generalization of the entanglement entropy to a virtual post-selection process. (2) the PE is holographically dual to the area of the minimal surface in a certain Euclidean “time-dependent” background. (3) the PE can play a role as a new quantum order parameter which detects whether two states are in the same quantum phase or not. Based on 2005.13801, 2011.09648, and work in progress.

Date/Place December 8th (Tue.) 15:30-16:30 / Online
Name Tomonori Ugajin (Kyoto Univ.)
　Title　 Entanglement between two disjoint universes (Slides)
Abstract We use the replica method to compute the entanglement entropy of a universe without gravity entangled in a thermofield-double-like state with a disjoint gravitating universe. Including wormholes between replicas of the latter gives an entropy functional which includes an ``island" on the gravitating universe. We solve the back-reaction equations when the cosmological constant is negative to show that this island coincides with a causal shadow region that is created by the entanglement in the gravitating geometry.At high entanglement temperatures, the island contribution to the entropy functional leads to a bound on entanglement entropy, analogous to the Page behavior of evaporating black holes. We also apply the formalism to black holes in de Sitter space, and find similar islands.

Date/Place December 1st (Tue.) 15:30-16:30 / Online
Name Matthew Dodelson (Kavli IPMU)
　Title　 Singularities of thermal correlators at strong coupling (Slides)
Abstract I will describe recent work with Ooguri on the singularities of the two point function at finite temperature in a conformal field theory in more than two dimensions. At weak coupling the only singularity is on the light cone, but in the large N, large lambda regime a new singularity emerges. This new singularity corresponds to a null geodesic in the AdS/Schwarzschild black hole, which may wrap the photon sphere many times. After deriving this result, I will discuss the resolution of these singularities by stringy tidal effects at finite lambda. The basic tool I will use is to take the Penrose limit around a given null geodesic, and then use the solubility of the string theory in this background. I will also discuss applications to rotating black holes.

Date/Place November 24th (Tue.) 15:30-16:30 / Online
Name René Sondenheimer (University of Graz)
　Title　 Physical observables of Brout-Englert-Higgs theories (Slides)
Abstract In this talk, I will discuss the phenomenological consequences of a strict gauge-invariant formulation of the Brout-Englert-Higgs mechanism. This requires a description of physical observables in terms of bound state structures. Although this seems to be at odds with the common treatment of electroweak particle physics at first glance, the properties of the bound states can be described in a perturbative fashion due to the Fröhlich-Morchio-Strocchi (FMS) framework. In particular a relation between the bound states and the elementary fields is obtained within Rξ gauges such that the main quantitative properties of the conventional description reappear at leading order of the FMS expansion. However, slight deviations of off-shell properties can be caused by the internal bound state structure. Further, I will show that the FMS approach provides a gauge-invariant Higgs spectral function which is not plagued by positivity violations or unphysical thresholds. In the second part, I will generalize the arguments of FMS to various gauge groups and demonstrate that the FMS approach allows us to put new constraints on theories beyond the standard model.

Date/Place November 17th (Tue.) 15:30-16:30 / Online
Name Tanmoy Mondal (KIAS)
　Title　 Phenomenological aspects of a light pseudoscalar in Type-X 2HDM (Slides)
Abstract A light pseudoscalar in the Type-X Two Higgs Doublet Model(2HDM) can explain muon anomalous magnetic moment. When produced, the pseudoscalar decays dominantly into tau leptons which leave a jetty signature at the LHC along with missing energy. Thus, it is not possible to reconstruct the mass of such light particles from the tau rich final states. In this talk, I will discuss the mass reconstruction of such a pseudoscalar and other heavy neutral/charged scalars at the LHC using the 2mu-2tau final state. Also, I will discuss the prospect of Yukawa production of a light (pseudo)scalar at a "Higgs factory" like ILC with sqrt(s)=250 GeV. I will show that it is possible to accommodate both electron and muon anomalous magnetic moment in the type-X 2HDM in presence of vector-like leptons.

Date/Place November 10th (Tue.) 15:30-16:30 / Online
Name Shinichiro Akiyama (Tsukuba U.)
　Title　 Tensor renormalization group approach to four-dimensional lattice field theories(Slides)
Abstract Tensor renormalization group (TRG) is a variant of real-space renormalization group to evaluate the partition function in the thermodynamic limit, without resorting to any probabilistic interpretation for the Boltzmann weight. The TRG can be formulated in a same manner for the systems with bosons, fermions, or both of them. Moreover, the parallel computation techniques and improvement of the TRG algorithm potentially enable us to investigate the four-dimensional systems, even in the parameter region where it is difficult to access with the standard Monte Carlo simulation. In this talk, we explain recent our numerical studies with the TRG approach to the lattice field theories in four dimensions.

Date/Place October 27th (Tue.) 15:30-16:30 / Online
Name Yoshihiko Abe (Kyoto U.)
　Title　 Electroweak Axion String and Superconductivity　(Slides)
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 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].

　

Date/Place October 20th (Tue.) 10:30-11:30 / Online
Name Masaru Hongo (Chicago U.)
　Title　 Anomaly matching for chiral transport phenomena　(Slides)
Abstract Hydrodynamics is a universal low-energy effective theory of conserved charge densities, which describes a long-distance and long-time behavior of many-body systems. Recently, it has been clarified that underlying quantum anomalies affect a hydrodynamic transport property, leading to peculiar transport phenomena known as the chiral magnetic effect and chiral vortical effect [1]. In this seminar, I will explain a field-theoretical derivation of the anomaly-induced chiral transport phenomena based on the anomaly matching for finite-temperature systems [2-3]. The crucial point for our derivation is a path-integral formula for local thermal equilibrium. Because of the thermal compactification, the thermodynamic functional is shown to be equipped with the Kaluza-Klein gauge symmetry attached to a thermally induced curved background. Using this symmetry structure, we can apply the anomaly matching condition for the thermodynamic potential, which provides a nonperturbative derivation of the anomaly-induced transport. I will also explain how we can use the Atiyah-Patodi-Singer index theorem to determine a transport coefficient related to a mixed global anomaly [4].
References: [1] D. T. Son and P. Surowka, Phys. Rev. Lett. 103, 191601 (2009). [2] M. Hongo, Annals of Physics, 383, 1 (2017). [3] M. Hongo, Y. Hidaka, Particles 2, 2, 261 (2019). [4] S. Golkar and S. Sethi, JHEP 1605, 105 (2016).

　

Date/Place October 13th (Tue.) 15:30-16:30 / Online
Name Yutaro Shoji (Hebrew U.)
Title Precise Calculation of the Decay Rate of False Vacuum with Multi-Field Bounce (Slides)
Abstract It has been discussed for a long time that the electroweak vacuum may not be absolutely stable in the standard model or in models beyond the standard model. The appearance of a deeper vacuum at a high energy scale makes the electroweak vacuum meta-stable and it finally decays through tunneling with a finite lifetime. If it is the case, we need to ensure that the lifetime is much longer than the age of the universe and the estimation of the lifetime is of great importance. The precise determination of the lifetime involving the quantum corrections from the gauge bosons is technically difficult and it is not until recently that a complete one-loop calculation became possible. We extend the previous result, which is applicable only to the case where only one scalar field is responsible for the decay, to the many-field case. It has great applicability such as to the color or charge breaking vacuums in the supersymmetric models.

　

Date/Place October 6th (Tue.) 15:30-16:30 / Online
Name Michihisa Takeuchi (Nagoya U.)
Title Higgs physics at LHC and future colliders (Slides)
Abstract After the discovery of the Higgs boson at LHC any other significant indication of new physics is found yet, although many physicist believe in existence of new physics beyond the LHC. Currently, the efforts of understanding the Higgs boson properties are on-going, which would be a portal for the new physics. I review the current status and the future prospect of the Higgs measurements and several examples how to detect new physics effects in the precision measurements of the Higgs properties.

　

Date/Place July 31 (Fri.) 13:30-14:30 /\ Online
Name Seok Kim (Seoul Natl. U.)
Title Black holes from anomalies
Abstract I will explain that some physics of large black holes in AdS can be accounted for by the background field method and the 't Hooft anomalies of the holographically dual CFTs.

Date/Place July 28 (Tue.) 15:30-16:30 / Online
Name Kohei Fujikura (Tokyo Inst. Tech.)
Title Observable Gravitational Waves in Minimal Scotogenic Model (Slides)
Abstract We scrutinise the widely studied minimal scotogenic model of dark matter (DM) and radiative neutrino mass from the requirement of a strong first order electroweak phase transition (EWPT) and observable gravitational waves at future planned space based experiments. The scalar DM scenario is similar to inert scalar doublet extension of standard model where a strong first order EWPT favours a portion of the low mass regime of DM which is disfavoured by the latest direct detection bounds. In the fermion DM scenario, we get newer region of parameter space which favours strong first order EWPT as the restriction on mass ordering within inert scalar doublet gets relaxed. While such leptophilic fermi on DM remains safe from stringent direct detection bounds, newly allowed low mass regime of charged scalar can leave tantalising signatures at colliders and can also induce charged lepton flavour violation within reach of future experiments. While we get such new region of parameter space satisfying DM relic, strong first order EWPT with detectable gravitational waves, light neutrino mass and other relevant constraints, we also improve upon previous analysis in similar model by incorporating appropriate resummation effects in effective finite temperature potential. This talk is based on arXiv: 2003.02276.

　

Date/Place July 21 (Tue.) 13:00-14:00 / Online
Name Toshifumi Noumi (Kobe U.)
Title Duality and Weak Gravity (Slides)
Abstract The Weak Gravity Conjecture predicts the existence of charged states whose masses are lower than their charges in appropriate units. The conjecture, if true, has a wide range of phenomenological applications from cosmology (inflation, dark matter) to particle physics (BSM physics). In this talk, toward a proof of the conjecture, I will discuss a role of positivity bounds and duality constraints on higher derivative effective interactions in demonstrating the conjecture. I will show that in a wide class of theories the conjecture follows from positivity bounds originating from unitarity and causality of UV scattering, whereas more detailed UV information such as duality symmetries is necessary to demonstrate the conjecture once dilaton is turned on.

　

Date/Place July 14 (Tue.) 15:30-16:30 / Online
Name Tetsuya Onogi (Osaka U.)
Title A conserved charge in general relativity (Slides)
Abstract How to define the energy has been a long-standing issue in general relativity from its beginning. There exist many different definitions but with some unsatisfactory points for each. We give a simple and precise definition of a conserved charge from covariantly conserved currents in general relativity, which enables us to define the energy in general relativity using the energy momentum tensor for the matter. Applying our formalism to blackholes, we succeeded in reproducing usual black hole masses, which justifies the interpretation that the energy of the blackhole is given by the matter energy at the origin. Next, applying our definition to a compact star, we find that there is a correction to the known mass formula associated with Oppenheimer-Volkoff equation. We also comment on the comparison with conventional methods such as ADM mass, Komar energy.

　

Date/Place July 7 (Tue.) 15:30-16:30 / Online
Name Masanori Hanada (Surrey U.)
Title Color Confinement and Bose-Einstein Condensation　(Slides)
Abstract We will argue that color confinement in large-N gauge theories and Bose-Einstein condensation in a system of of N identical bosons take place due to the common underlying mechanism.　We argue that partially-confined, partially-deconfined phase, in which SU(M) subgroup of SU(N) gauge group deconfines, exists between completely confined phase and completely deconfined phases. In the weak-coupling regime, we describe this phase analytically, by using the techniques developed by Aharony and collaborators in 2003. (If time permits, we show the evidence at strong coupling as well, by using the Monte Carlo method.) Based on this "partial confinement" picture, we propose a unified description of color confinement in the large-N gauge theory and Bose-Einstein condensation (BEC) in the system of identical bosons. Indistinguishability associated with the symmetry group --- SU(N) in gauge theory, and S_N permutations in the system of identical bosons --- is crucial for the formation of the condensed (confined) phase. We relate standard criteria, based on off-diagonal long range order (ODLRO) for BEC and the Polyakov loop for gauge theory. The constant offset of the distribution of the phases of the Polyakov loop corresponds to ODLRO. (As a byproduct, we define the “Polyakov loop” in the system of N identical bosons, and see that the formation of BEC is nothing but “Gross-Witten-Wadia transition”.) This viewpoint may have implications for confinement at finite N, and for quantum gravity via gauge/gravity duality.

　

Date/Place June 30 (Tue.) 15:30-16:30 / Online
Name Koji Ishiwata (Kanazawa U.)
Title Superconformal subcritical hybrid inflation and leptogenesis (Slides)
Abstract We consider D-term hybrid inflation in the framework of superconformal supergravity. In part of the parameter space, inflation continues for subcritical inflaton field value. Consequently, a new type of inflation emerges, which gives predictions for the scalar spectral index and the tensor-to-scalar ratio that are consistent with the Planck data. We extend this scenario to introduce three right-handed neutrinos. In the model one of the right-handed sneutrinos plays a role of the inflaton field, and it decays to reheat the universe after inflation. Then thermal leptogenesis or sneutrino leptogenesis is realized.

　

Date/Place June 23 (Tue.) 15:30-16:30 / Online
Name Tanmoy Modak (NTU)
Title Signatures of additional top and bottom Yukawa couplings at the LHC (Slides)
Abstract In this talk I will discuss about possible direct and indirect signatures of additional top and bottom Yukawa couplings that might exist in nature. The context is general Two Higgs Doublet Model. Such additional Yukawa couplings can account for the observed Baryon Asymmetry of the Universe and can have exquisite signatures at the LHC and Belle-II experiments.

　

Date/Place June 16 (Tue.) 15:30-16:30 / Online
Name Yu Hamada (Kyoto U.)
Title Sphaleron from gradient flow (Slides)
Abstract The sphaleron, which is a static and unstable solution to EOMs, plays a crucial role to explain the baryon asymmetry in our universe. In general, it is difficult to obtain the sphaleron solution without imposing any ansatz due to the instability. In this talk, we propose a simple method to obtain the sphalerons using gradient flow. By adding a modification term to the gradient flow equation, we can obtain the sphaleron as a stable fixed point of the flow equation. We will show a result of applying the method to the SU(2)-Higgs model in four dimensions. This talk is based on arXiv:2003.02070.

　

Date/Place June 9 (Tue.) 16:00-17:00 / Online
Name Okuto Morikawa (Kyushu U.)
Title Computer simulation of the N=2 Landau-Ginzburg model (Slides)
Abstract The two-dimensional N=2 Wess-Zumino model is believed to provide the Landau-Ginzburg description of an N=2 superconformal field theory. Since this model is strongly coupled at IR, it is difficult to prove this theoretical conjecture. In this talk, to systems with various superpotentials, I apply a SUSY-preserving numerical algorithm based on the Nicolai map. I show that we can measure the scaling dimension and the central charge, and obtain results which are consistent with the conjectured correspondence. I would like to remark that this numerical approach will be useful to investigate a superstring theory via the Landau-Ginzburg/Calabi–Yau correspondence.

　

Date/Place June 2nd (Tue.) 15:30-16:30 / Online
Name Satoshi Shirai (Kavli IPMU)
Title Cornering Higgsino at the LHC (Slides)
Abstract A Higgsino-like particle is an attractive candidate for the WIMP dark matter. Thanks to the electroweak interac tion, the production cross section of the Higgsino at the LHC is rather high. Even for the 1 TeV Higgsino, the LHC run 2 could produce O(100) Higgsino particles. However the huge Standard Model background prevents the Higgsino discovery and the present LHC sensitivity can be even worse than the LEP result in some parameter region. In this talk, I discuss a new search strategy to explore such a parameter region by utilizing exotic tracks from the charged Higgsino: soft displaced track and disappearing track.

　

Date/Place May 19 (Tue.) 15:30-16:30 / Online
Name Daisuke Nomura (KEK)
Title The muon g-2: a new data-based analysis (Slides)
Abstract Following updates in the compilation of e+e- --> hadrons data, this work presents reevaluations of the hadronic vacuum polarization contributions to the anomalous magnetic moment of the muon (a_{\mu}). Combining the results for the hadronic vacuum polarization contributions with recent updates for the hadronic light-by-light corrections, the electromagnetic and the weak contributions, the deviation between the measured value of a_{\mu} and its Standard Model prediction amounts to \Delta a_{\mu} = (28.02 \pm 7.37) x 10^{-10}, corresponding to a muon g-2 discrepancy of 3.8 \sigma.

　

Date/Place May 12 (Tue.) 10:30-11:30 / Online
Name Akio Tomiya (Riken BNL)
Title Lattice gauge theory with quantum computers (Slides)
Abstract In this talk, we discuss our quantitative study of lattice gauge theory towards using quantum computers. Quantum computer enables us to investigate quantum systems, like field theory, in the Hamiltonian formalism, which is not suffered from the infamous sign problem. However, in the Hamiltonian formalism, in order to calculate vacuum expectation values, we have to prepare the ground state of the target Hamiltonian, and this is non-trivial. By using the adiabatic theorem for the state preparation, we reproduce both of the exact results of the massless Schwinger model and approximated ones for the massive Schwinger model within controlled systematic errors from the state preparation. We assume that most of the audience are not experts. This talk is based on arXiv: 2001.00485.

　

Date/Place April 28th (Tue.) 15:30-16:30 / Online
Name Ryo Nagai (INFN Padua and Padua U.)
Title Toward a Generalization of Higgs Effective Field Theory (Slides)
Abstract Effective field theory (EFT) is a powerful tool for investigating physics beyond the standard model (SM). In this talk, we will discuss how to construct a general EFT framework for the (extended) Higgs sector and its phenomenological application. I will introduce a general method for formulating the EFT, which is so-called “CCWZ coset construction”. Applying the method, we will discuss (i) how to parameterize the Higgs interactions in a model-independent way and (ii) how to introduce the new particles in the EFT framework. This talk is based on 1904.07618 and our on-going works.

　

過去のセミナー