2023年度のセミナー
| Date/Place | January 29th (Mon.) 11:00-12:00 / H701 |
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| Name | Kohei Kamada (University of Chinese Academy of Science) |
| Title | Higgs Inflation in Einstein-Cartan Gravity and its UV Extension |
| Abstract | The Standard Model Higgs is the unique (possibly) fundamental scalar field we have confirmed its existence thus far. Investigating the possibility if it can drive inflation that explains the present Universe is one of the most important problems in cosmology. Indeed, with a large non-minimal coupling between the Ricci scalar and the Higgs field, the observed cosmological perturbations are generated by Higgs inflation both in metric and Palatini formalisms. Moreover, they are smoothly connected with the help of non-minimal Nieh-Yan term in the Einstein-Cartan gravity. However, the relatively small strong coupling scale in these models has been thought to be perhaps problematic, especially at the (p)reheating epoch, and calls for their UV extensions. While the Ricci scalar squared term naturally (from the renormalization of the scalar sector) extends the strong coupling scale to the Planck scale in the metric formalism while it does not in the Palatini formalism. In this talk, I will investigate the renormalization of the Higgs inflation in the Einstein-Cartan formalism and show how the Ricci scalar squared term is generally "required" for the renormalization and UV-extends the theory. We clarify how it behaves in the Palatini limit where the theory is not UV-extended by the Ricci scalar squared term. |
| Date/Place | January 23th (Tue.) 15:40-16:40 / H701 |
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| Name | Katsuya Hashino (Fukushima Collage) |
| Title | Exploring new physics effects through gravitational waves from first-order phase transition |
| Abstract | There are some phenomena that the standard model (SM) cannot explain, such as the baryon asymmetry of the universe, and thus the new physics effects beyond the SM are necessary to explain them. The new effects could potentially act as the cause of first-order phase transition in the early universe. The production of gravitational waves (GWs) is known to occur if such a first-order phase transition takes place. The GWs travel through the universe virtually unimpeded, giving us information about the potential of the early universe. In this talk, I will show the possibility of exploring new physics effects through GW observations. |
| Date/Place | January 16th (Tue.) 15:40-16:40 / H701 |
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| Name | Takahiro Yokokura (Tohoku U.) |
| Title | The QCD phase diagram via 't Hooft anomalies |
| Abstract | The QCD phase diagram in the space of temperature and imaginary baryon chemical potential has been an interesting subject. However it is difficult to solve QCD analytically because of strong coupling. On the other hand, a notion of an anomaly has been extended in the last decade. In particular an anomaly in the space of coupling constants, which is a generalization of a 't Hooft anomaly, is useful to study a phase diagram because it directly constrains possibilities of the phase diagram. In this talk, I will talk about analysis of the QCD phase diagram by using an anomaly in the space of imaginary chemical potential. First I will explain an anomaly in the space of coupling constants using a free boson on a circle with a theta angle θ. It is important that a phase transition happens in the range of θ=0 to θ=2π. Second I will discuss the anomaly in the space of chemical potential and its implication of the QCD phase diagram. The partition function of QCD has 2π - periodicity of imaginary chemical potential. However the periodicity is broken when we gauge the chiral symmetry of QCD. It is just regarded as the anomaly in the space of coupling constants. This anomaly is analogue to the anomaly in the space of the theta angle of the boson on the circle. Similar to the case of the free boson on the circle, we can constrain the QCD phase diagram. In QCD case, not only a phase transition but also SSB happens in the 2π range of imaginary chemical potential. Finally I will discuss possible degrees of freedom about particular possibilities of phase diagrams. |
| Date/Place | January 9th (Tue.) 15:40-16:40 / H701 |
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| Name | Nobuhiro Maekawa (Nagoya U.) |
| Title | Recent developments on the giant-graviton expansion |
| Abstract | After we review the natural GUT which made me convincing twenty years ago that the grand unified theory must be the true theory beyond the standard model, we discuss its problems, which may be hints for the model beyond the GUT. Finally I will introduce a trial to solve one of the problems and discuss the implication for the model beyond the GUT. |
| Date/Place | December 22th (Fri.) 13:00-14:00 / H701 |
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| Name | Yoshimasa Hidaka (KEK) |
| Title | Hamiltonian lattice gauge theory and application to nonequilibrium and dense QCD |
| Abstract | I present an approach to lattice QCD using the Hamiltonian formalism for nonequilibrium and finite density. This approach can circumvent the sign problem of QCD that arises from importance sampling. Because the gauge theory has infinite-dimensional Hilbert space even on a finite lattice, due to the gauge field being a boson, and because of the large redundancy in degrees of freedom associated with gauge symmetry, it is necessary to introduce regularization to perform calculations. To this end, we employ a q-deformed gauge theory as a regularization technique that preserves the properties of the original gauge theory. As applications of Hamiltonian formalism, I show our results on the thermalization process on a small lattice system, and the thermodynamic behavior at finite density in a (1+1)-dimensional system using the density matrix renormalization group technique. |
| Date/Place | December 12th (Tue.) 15:40-16:40 / H701 |
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| Name | Shota Fujiwara (Witwatersrand U.) |
| Title | Recent developments on the giant-graviton expansion |
| Abstract | Recently, a new method for calculating the superconformal index, called the giant-graviton expansion, has been established. This method calculates superconformal indices of SCFTs from the holographic dual string theory on AdS spacetime. Specifically, the giant-graviton expansion contains the contribution of wrapped branes (giant-gravitons) as a finite-N correction to the large-N indices, and indices of SCFTs of any rank N can be calculated exactly. In this talk we will study recent developments on the giant-graviton expansion and also discuss “the duality” aspect associated to it. |
| Date/Place | December 7th (Thu.) 15:00- / H701 |
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| Name | 吉村太彦 (東京大学名誉教授) |
| Title | 「素粒子と宇宙：ある遍歴」(Slides) |
| Abstract | 素粒子の標準理論は、多くの高エネルギー実験結果で示されたように、ほぼ破綻なく成立していることは間違いない。標準理論を超える唯一のヒントはニュートリノ振動の発見による小さな有限質量であろう。一方、宇宙論からインフレーションと暗黒エネルギーの問題が新たなスカラー場の存在を示唆し、スカラー自由度がどのように標準理論と関係するかが問われている。講演者は、最近、スカラー自由度を含めた新たな重力理論の必要性に注目した理論展開に関わるようになった。ここに至る道筋も含めて素粒子と宇宙のかかわりについてお話したい。 |
| Date/Place | December 5th (Tue.) 15:40-16:40 / H701 |
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| Name | Kei Yamamoto (Hiroshima Institute of Technology) |
| Title | Interplay of new physics effects in muon g-2, EDM and LFV with U(2) flavor symmetry |
| Abstract | The electric and magnetic dipole moments of the electron and the muon are low-energy probes of New Physics (NP) beyond the Standard Model (SM). The recent experimental measurement of the anomalous magnetic moment of the muon has indicated the discrepancy with the SM prediction. The long-standing muon g-2 anomaly might be a hint for new physics. In this seminar, after brief review of U(2) flavor symmetry, I will discuss the interplay of NP among the lepton magnetic moment, the lepton flavor violation (LFV) and the electron electric dipole moment (EDM) in light of recent data of the muon g-2, in the SMEFT with the U(2) flavor symmetry. |
| Date/Place | November 28th (Tue.) 16:40-17:40 / H701 |
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| Name | Tomo Takahashi (Saga U.) |
| Title | Muti-dimensional perspectives on the Inflationary Universe (Slides) |
| Abstract | I discuss the inflationary Universe from "multi-dimensional" perspectives. In the first part, I consider a multi-dimensional field space for the inflationary dynamics and discuss the predictions for primordial fluctuations in such a framework, taking the sneutrino inflation model as an example. I discuss how we can construct an inflationary model consistent with current observations even with inflaton potentials which are already excluded in the single-field framework. In the second part, I talk about a "multi-dimensional" test of inflation, in which various probes are utilized. Future prospects, including those from the future CMB polarization experiment LiteBIRD in combination with other probes will be given. A possible test with the quantum nature of primordial fluctuations, such as using quantum discord, is also briefly discussed. |
| Date/Place | November 21th (Tue.) 15:40-16:40 / H701 |
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| Name | Motokazu Abe (Kyusyu U.) (Slides) |
| Title | Fractional topological charge in lattice SU(N) gauge theories coupled with Z_N 2-form gauge fields |
| Abstract | We extend the definition of L\"uscher's lattice topological charge to the case of 4d SU(N) gauge fields coupled with Z_N 2-form gauge fields. This result is achieved while maintaining the locality, the $SU(N)$ gauge invariance, and Z_N 1-form gauge invariance, and we find that the manifest 1-form gauge invariance plays the central role in our construction. This result gives the lattice regularized derivation of the mixed 't~Hooft anomaly in pure $SU(N)$ Yang--Mills theory between its Z_N 1-form symmetry and the θ periodicity. |
| Date/Place | November 14th (Tue.) 15:40-16:40 / H701 |
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| Name | Kimiko Yamashita (Ibaraki U.) |
| Title | Positivity Bounds on Higgs-Portal Dark Matter |
| Abstract | We consider the positivity bounds for WIMP scalar dark matter with effective Higgs-portal couplings up to dimension-8 operators. Taking the superposed states for Standard Model Higgs and scalar dark matter, we show that the part of the parameter space for the effective couplings, otherwise unconstrained by phenomenological bounds, is ruled out by the positivity bounds on the dimension-8 derivative operators. We find that dark matter relic density, direct and indirect detection, and LHC constraints are complementary to the positivity bounds in constraining the effective Higgs-portal couplings. We also consider the relic density and positivity bounds for freeze-in scalar dark matter. |
| Date/Place | November 7th (Tue.) 15:40-16:40 / H701 |
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| Name | Mohammad Akhond (Kyoto U.) |
| Title | 5d SCFTs and their non-supersymmetric cousins |
| Abstract | I will argue that combining old ideas such as dualities and exact results in SUSY QFTs supplemented with recent techniques such as SPT phases and generalised anomalies can shed light on strong coupling dynamics of non-SUSY theories. I will in particular show that non-SUSY gauge theories, which are related to SUSY SCFTs by RG in 5d exhibit phase transitions in the UV which are candidates for non-SUSY fixed points. |
| Date/Place | October 24th (Tue.) 15:40-16:40 / H701 |
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| Name | Akira Matsumoto(YITP) |
| Title | Three ways of calculating composite-particle spectra of gauge theories in the Hamiltonian formalism |
| Abstract |
Determination of the mass spectrum of composite particles (hadrons) is one of the key issues in QCD,
which has been precisely calculated by the Monte Carlo simulation based on the Lagrangian formalism.
We newly consider three distinct methods to compute the mass spectrum in the Hamiltonian formalism,
where we can apply quantum computation and tensor network methods.
The first one, the correlation-function scheme, corresponds to the conventional Euclidean method in the Monte Carlo study.
The second one, the one-point-function scheme, uses the boundary effect to compute the mass spectrum efficiently.
The third one, the dispersion-relation scheme, generates the excited states to obtain the dispersion relation and quantum numbers.
These methods are demonstrated using the density-matrix renormalization group (DMRG) in the 2-flavor Schwinger model,
which shares important properties with QCD.
We show that their results are consistent with each other, and discuss their potential applications. (preprint: https://arxiv.org/abs/2307.16655) |
| Date/Place | October 17th (Tue.) 15:40-16:40 / H701 |
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| Name | Emily Nardoni(IPMU) |
| Title | Duality of Adjoint SQCD from Argyres-Douglas Theories |
| Abstract | The possible conformal fixed points of N=1 adjoint SQCD in four dimensions follow an ADE classification, with some of these SCFTs conjectured to participate in Seiberg-like dualities. In this talk, I will discuss a new proposed dual description of some of these fixed points, and provide various consistency checks of the proposal. The duals are built from a class of strongly-coupled N=2 SCFTs of Argyres-Douglas type, coupled to matter and deformed by N=1 preserving deformations. |
| Date/Place | October 3rd (Tue.) 15:40-16:40 / H701 |
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| Name | Ke-pan Xie(Beihang U.) |
| Title | Matter, dark matter and primordial black holes from first-order phase transitions |
| Abstract | The longstanding puzzles of matter-antimatter asymmetry and dark matter point to the need for physics beyond the Standard Model. A first-order phase transition (FOPT) in the early Universe could provide the necessary conditions for baryogenesis, the generation of dark matter and even primordial black holes. This talk will discuss the basics of cosmic FOPTs and recent developments in relevant new physics mechanisms. |
| Date/Place | August 1st (Tue.) 15:40-16:40 / H701 |
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| Name | Naoya Kitajima(Tohoku U.) |
| Title | Cosmological production of stochastic gravitational waves with ultra-low frequencies |
| Abstract | In this seminar, I will show the production of stochastic gravitational waves (GWs) in the early universe based on the physics beyond the standard model. I particularly focus on the GWs from (i) parametric resonance instability in the (axion-like) early dark energy model, (ii) decay of axion (ALP) domain walls associated with the QCD phase transition, (iii) network of Abelian-Higgs cosmic strings with the emission of light vector boson (dark photon). Those models predict GWs in ultra-low frequency bands, namely femto-Hz or nano-Hz bands, which can be probed by cosmic microwave background observations or pulsar timing observations. We have performed numerical lattice simulations to follow the nonlinear dynamics of scalar field and also to follow the subsequent GW emission process. I will show the resultant GW spectrum in each modeI and also show the implication for the stochastic GW detection recently reported by the NANOGrav Collaboration. |
| Date/Place | July 25th (Tue.) 15:40-16:40 / H701 |
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| Name | Arata Yamamoto (Tokyo U.) |
| Title | Chiral fermion in the Hamiltonian lattice gauge theory |
| Abstract | The Nielsen-Ninomiya no-go theorem prohibits the existence of naive chiral symmetry on the lattice. A famous solution to this problem is the overlap fermion. Although the overlap fermion is well established in the path integral formalism, it is not in the Hamiltonian formalism. I will talk about the overlap fermion and its property in the Hamiltonian formalism. I will also show the application to quantum computing. |
| Date/Place | July 11th (Tue.) 15:40-16:40 / H701 |
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| Name | Tomohiro Abe (Tokyo Univ of Science) |
| Title | A pseudo-Nambu-Goldstone dark matter model and direct detection experiments. |
| Abstract | Dark matter is one of the mysteries in our Universe. There are so many ideas that explain dark matter. The Weakly Interacting Massive Particle (WIMP) is a popular DM scenario in particle physics. In the WIMP scenario, the DM particles interact with the SM particles, and thus there are various processes. DM annihilation processes are essential to explain the measured value of the energy density of the DM by the freeze-out mechanism. The same interaction predicts the creation of the DM particles from the SM particles and motivates the search for DM at collider experiments. The interaction also implies the DM-SM scattering processes, which are utilized for DM direct detection. After reviewing WIMP dark matter scenario briefly, I will discuss a pseudo-Nambu-Goldstone DM model that can explain the null results in the recent direct detection experiments. |
| Date/Place | July 18th (Tue.) 15:40-16:40 / H701 |
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| Name | Thanaporn Sichanugrist (Tokyo U.) |
| Title | Detection of hidden photon dark matter using the direct excitation of transmon qubits |
| Abstract |
We propose a novel dark matter detection method utilizing the excitation of superconducting transmon qubits. Assuming the hidden photon dark matter of a mass of O(10) µeV, the classical wave-matter oscillation induces an effective ac electric field via the small kinetic mixing with the ordinary photon. This serves as a coherent drive field for a qubit when it is resonant, evolving it from the ground state towards the first-excited state. We evaluate the rate of such evolution and observable excitations in the measurements, as well as the search sensitivity to the hidden photon dark matter. For a selected mass, one can reach ɛ~10^{-13}-10^{-12} (where ɛ is the kinetic mixing parameter of the hidden photon) with a few tens of seconds using a single standard transmon qubit. A simple extension to the frequency-tunable SQUID-based transmon enables the mass scan to cover the range of 4-40 µeV (1-10 GHz) within a reasonable length of run time. The scheme has great potential to extend the sensitivity towards various directions including being incorporated into the cavity-based haloscope experiments or the currently available multi-bit Noisy Intermediate-Scale Quantum (NISQ) computer machines.
Based on: S. Chen, H. Fukuda, T. Inada, T. Moroi, T. Nitta, T. Sichanugrist, Detection of hidden photon dark matter using the direct excitation of transmon qubits, arXiv: 2212.03884 [hep-ph] |
| Date/Place | July 4th (Tue.) 15:40-16:40 / H701 |
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| Name | Masahiro Hotta (Tohoku U.) |
| Title | Expanding Edges of Quantum Hall Systems in a Cosmology Language – Hawking Radiation from de Sitter Horizon in Edge Modes |
| Abstract | Expanding edge experiments are promising to open new physics windows of quantum Hall systems. In a static edge, the edge excitation, which is described by free fields decoupled with the bulk dynamics, is gapless, and the dynamics preserve conformal symmetry. When the edge expands, such properties need not be preserved. We formulate a quantum field theory in 1+1 dimensional curved spacetimes to analyze the edge dynamics. We propose methods to address the following questions using edge waveforms from the expanding region: Does the conformal symmetry survive? Is the nonlinear interaction of the edge excitations induced by edge expansion? Do the edge excitations interact with the bulk excitations? We additionally show that the expanding edges can be regarded as expanding universe simulators of two-dimensional dilaton-gravity models, including the Jackiw-Teitelboim gravity model. As an application, we point out that our theoretical setup might simulate emission of analog Hawking radiation with the Gibbons-Hawking temperature from the future de Sitter horizon formed in the expanding edge region. Recent status of the experiment will be also reported. |
| Date/Place | June 30th (Fri.) 16:50-17:50 / D401 |
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| Name | Takehiko Asaka (Niigata Univertsity) |
| Title | What can we learn from neutrinoless double beta decays in the seesaw mechanism? |
| Abstract | Origin of neutrino masses is one of the most important problems in physics today. The scenarios with the seesaw mechanism by introducing right-handed neutrinos is very attractive since it can naturally explain the smallness of neutrino masses observed by experiments. In the seesaw mechanism neutrinos are massive Majorana particles, and the lepton number, which is the accidental symmetry of the Standard Model, is broken, which leads to the non-standard phenomenon. One important example is the neutrinoless double beta decays. In this seminar, we consider the case when right-handed neutrinos are lighter than TeV scale and show how the properties of right-handed neutrinos (masses, mixing elements etc) can be probed by the neutrinoless double beta decays. |
| Date/Place | June 27th (Tue.) 15:40-16:40 / H701 |
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| Name | Masazumi Honda (YITP) |
| Title | Digital quantum simulation of higher-charge Schwinger model with topological term |
| Abstract |
I am going to talk about application of quantum computation to numerical simulation of quantum field theory. Specifically we implement a digital quantum simulation of a gauge theory with a topological term in Minkowski spacetime, which is practically inaccessible by standard lattice Monte Carlo simulations.
We focus on 1+1 dimensional quantum electrodynamics with a topological term and a charge-q Dirac fermion known as the Schwinger model.
We construct the true vacuum state of a lattice Schwinger model using adiabatic state preparation which, in turn, allows us to compute an expectation value of the fermion mass operator with respect to the vacuum.
Upon taking a continuum limit we find that our result in massless case agrees with the known exact result.
In massive case, we find an agreement with mass perturbation theory in small mass regime and deviations in large mass regime.
We also study a potential between heavy charged particles and see that the potential changes its qualitative behavior as changing parameters:
it shows confinement, screening and an exotic behavior called negative tension behavior
in which particles with opposite charges repel with each other. Refs:
|
| Date/Place | June 20th (Tue.) 15:40-16:40 / H601 |
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| Name | Takato Mori (YITP) |
| Title | Causality and entanglement on brane from scattering in the bulk |
| Abstract |
In recent years, holography in the presence of branes, especially double holography, has attracted a great deal of attention, e.g. to the black hole evaporation, Randall-Sundrum-like brane cosmology, and the AdS/BCFT. In double holography, there exists three equivalent pictures. In addition to the usual bulk and boundary perspectives, there is an intermediate perspective where the brane is coupled to a nongravitating bath. However, it has been pointed out that in the presence of such a brane, fundamental properties such as causality and subadditivity are violated. Since the latter is a property that any quantum systems must satisfy, its violation makes the existence of the intermediate picture doubtful.
In this talk, I carefully examine causality of the intermediate picture by considering a particular scattering that requires a connected entanglement wedge. As a result, we show that naive causality undergoes modification and subadditivity is preserved. This talk is based on work in preparation with Beni Yoshida. |
| Date/Place | June 13th (Tue.) 15:40-16:40 / H701 |
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| Name | Yu Nakayama (YITP) |
| Title | Scale vs Conformal |
| Abstract | In this talk, I review recent development in the distinction and relation between scale invariance and conformal invariance. I first show the argument for the enhancement from scale invariance to conformal invariance based on the dilaton effective action in two and four dimensions. While the situation in three dimensions is generically open, if I focus on specific theories, I can show the enhancement: an example is the non-linear sigma model due to Perelman's theorem. If we relax the assumption of the reflection positivity, there are some examples of scale-invariant but non-conformal interacting field theories. A dipolar magnet, physically realized in nature, is one example. We investigate the non-renormalization property of the non-conserved current operator in interacting field theories, which is necessary for scale invariance without conformal invariance. |
| Date/Place | June 6th (Tue.) 15:40-16:40 / H701 |
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| Name | Taiichi Nakanishi (YITP) |
| Title | Multipole conserving field theory and the fracton phase |
| Abstract | Fractons are quasi-particles with exotic properties; they cannot move alone. These particles are originally studied enthusiastically in the field of quantum information or condensed matter physics, because they show up in spin models with quantum error correcting mechanisms. Recently, fractons have gathered interest from high energy physicists, because the field theories describing fractons have many novel and exotic features which do not found in conventional theories. In this talk, I will explain some spin models with fractonic excitations and some progress in the multipole conserving field theory, that describes fractonic particles. This talk is based on JHEP 03(2023) 188 [arXiv:2212.13006] and an on-going joint work with Masazumi Honda and Hiromi Ebisu. |
| Date/Place | May 30th (Tue.) 15:40-16:40 / H701 |
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| Name | Maki Takeuchi (Kobe U.) |
| Title | The Mystery of the Standard Model and the Extra-Dimensional Model |
| Abstract | The Standard Model achieved significant success with the discovery of the Higgs in 2012. However, there are still numerous unexplained phenomena. One of them is the number of generations problem, where quarks and leptons come in three copies with only differences in mass while having identical spin and charge. Is the existence of these three generations a mere coincidence, or is there a deeper reason behind it? The Standard Model cannot explain why there are three generations. On the other hand, the higher dimensional theory offers a possible explanation for the number of generations problem. In the higher dimensional theory, the number of generations is related to the geometry of the extra dimensions. In other words, the number of generations carries a physical meaning associated with the geometry of the extra dimensions. In this seminar, I will talk about the generation structure of the T^2/Z_N orbifold with magnetic flux. |
| Date/Place | May 16th (Tue.) 15:40-16:40 / H701 |
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| Name | Daichi Takeda (Kyoto U.) |
| Title | Spacetime-emergent ring toward tabletop quantum gravity experiments |
| Abstract | The AdS/CFT correspondence indicates the existence of quantum materials equivalent to higher-dimensional gravity systems, and the discovery of such materials will open up new possibilities for quantum gravity experiments. In this talk, we propose a method to identify ring-shaped materials holographically governed by gravitational theories on the pure AdS$_3$ in the low-temperature phase. When a local source $J$ is applied to such a ring, the response function behaves as if the source effect had propagated on the dual curved spacetime inside the bulk. By optically imaging the response data, we capture the virtual image of $J$ that the gravitational lens creates. Since in the pure AdS$_3$ all null geodesics shot from a boundary point reach the antipodal point, we observe the virtual image only there, which is the signal of the spacetime emergence. We also discuss the experimental parameters and their feasibility. |
| Date/Place | May 23th (Tue.) 15:40-16:40 / H701 |
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| Name | Juntaro Wada (U. of Tokyo) |
| Title | Revisiting Affleck-Dine Leptogenesis with light sleptons |
| Abstract | We revisit the Affleck-Dine leptogenesis via the LHu flat direction with a light slepton field. Although the light slepton field is favored in low-energy SUSY phenomenologies, such as the muon g-2 anomaly and bino-slepton coannihilation, it may cause a problem in the Affleck-Dine leptogenesis: it may create an unwanted charge-breaking vacuum in the Affleck-Dine field potential so that the Affleck-Dine field is trapped during the course of leptogenesis. We investigate the conditions under which such an unwanted vacuum exists and clarify that both thermal and quantum corrections are important for the (temporal) disappearance of the charge-breaking minimum. We also confirm that if the charge-breaking vacuum disappears due to the thermal or quantum correction, the correct baryon asymmetry can be produced while avoiding the cosmological gravitino problem. |
| Date/Place | May 9th (Tue.) 15:40-16:40 / H701 |
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| Name | Sunil Sake (Osaka U.) |
| Title | Sparse RMT and Sparse SYK |
| Abstract | SYK model can be thought of as a sparse random matrix, with only a fraction of the full random matrix elements taken to be non-zero. To explore the universality of the properties of the SYK model, we study numerically the properties of the sparse random matrices of the standard ensemble, namely GUE/GOE. We study the behaviour of the system as the randomness is changed, by varying the type and number of coupling constants and the variance of their probability distributions. We analyse various features including the density of states and the Spectral form factor, as well as features tied to chaos like level statistics, Out-of-time ordered correlators and operator growth. We also analyze a particular sparse version of SYK model obtained by setting some of the couplings of the SYK model to vanish. |
| Date/Place | April 25th (Tue.) 15:40-16:40 / H701 |
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| Name | Dongsheng Ge (Osaka U.) |
| Title | Boundary induced dynamical phase transition via inhomogeous quenches |
| Abstract | Boundary effects play an interesting role in the finite-size physical systems. Those are reminiscent of the choices of the boundary conditions. In this work, we study the boundary induced dynamical properties in the “1+1”-dimensional critical systems, driven by the inhomogeneous quenches of SSD and Möbius types. We find that different boundary conditions measured by the boundary entropy lead to different scenarios of phase transitions. We give a holographic interpretation in terms of intersecting branes in AdS3. |
| Date/Place | April 18th (Tue.) 15:40-16:40 / H701 |
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| Name | Akanksha Bhardwaj (Glasgow U.) |
| Title | Graph Neural Network: Its Applications to Constrain BSM Models and EFTs |
| Abstract |
Graph Neural Networks have emerged as a powerful tool for operating on graph-structured data, facilitating the exploration of non-Euclidean physics data.
In this talk, I will first discuss an autoencoder-based strategy to facilitate anomaly detection for boosted jets, employing Graph Neural Networks (GNNs).
To overcome the known limitations of GNN autoencoders, we design a symmetric decoder capable of simultaneously reconstructing edge features and node features.
Next, I will discuss the application of GNNs in a supervised scenario where we explore its potential to improve high-dimensional effective field theory parameter fits to collider data beyond traditional rectangular cut-based differential distribution analyses. As a specific case, we focus on an SMEFT analysis of pp → top pair production, including top decays, where the linear effective field deformation is parameterized by thirteen independent Wilson coefficients. The application of GNNs allows us to condense the multidimensional phase space information available for the discrimination of BSM effects from the SM expectation by considering all available final state correlations directly. |
| Date/Place | April 11th (Tue.) 15:40-16:40 / H701 |
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| Name | Nicolo Zenoni (Osaka U.) |
| Title | Complexity in (hybrid) de Sitter spacetime |
| Abstract |
Holographic volume [1] and action [2,3] complexity are supposed to probe the geometry beyond horizons. For a black hole in anti-de Sitter (AdS) spacetime, complexity asymptotically increases at a constant rate, as the Einstein-Rosen bridge behind the event horizon [5].
In de Sitter (dS) spacetime, instead, complexity manifests a hyperfast growth [6], due to the inflationary expansion of spacetime beyond the cosmological horizon [7]. In this seminar, we consider geometries interpolating between AdS and dS. In particular, we present the time evolution of volume complexity in a class of three-dimensional hybrid geometries representing an AdS black hole with a dynamical dS bubble in its interior [8].
We show that, depending on the dynamics of the bubble, complexity behaves qualitatively either as in the AdS black hole or as in the dS case [9].
We then specialize to two-dimensional dS in Jackiw-Teitelboim gravity, and we point out that the dilaton is crucial for complexity to behave as in higher dimension [10]. While volume complexity needs a proper Weyl field-redefinition to mimicking the higher-dimensional result, action complexity naturally meets this expectation.
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