iTHEMS Theoretical Physics Seminar
76 events

Seminar
Algebraic curves and parametric resurgence
July 29 (Mon) at 16:30  17:45, 2024
Samuel Crew (Postdoctoral Fellow, Imperial College London, UK)
In this talk I will discuss recent work together with Ines Aniceto (Southampton) on algebraic examples of parametric resurgence. We discuss a simple example to elucidate the socalled higher order Stokes phenomena and discuss how a Borel innerouter matching procedure allows us to view parametric resurgence as a series of nonparametric resurgence problems.
Venue: Hybrid Format (3F #359 and Zoom), Main Research Building
Event Official Language: English

Seminar
Thermal radiation exchange in primordial gravitational waves
July 18 (Thu) at 13:30  15:00, 2024
Atsuhisa Ota (Postdoctoral Fellow, Institute for Advanced Study, Hong Kong University of Science and Technology, China)
The radiationdominated universe is a key component of standard Big Bang cosmology. Radiation comprises numerous quantum elementary particles, and its macroscopic behavior is described by taking the quantum thermal average of its constituents. The dynamics of gravitational waves are considered in this smooth fluid. While interactions between individual particles and gravitational waves are often neglected in this context, it raises the question of whether such a hydrodynamical approximation is reasonable. To address this question, we explored the quantum mechanical aspects of gravitational waves in a universe dominated by a massless scalar field, whose averaged energymomentum tensor serves as background radiation. We computed thermal loop corrections for the gravitational wave power spectrum using the SchwingerKeldysh formalism. Interestingly, we found that the loop effect enhances the superhorizon primordial gravitational wave spectrum, indicating that the inflationary spectrum is not conserved, contrary to conventional wisdom. These findings have significant implications for our understanding of the early universe. In this talk, I will begin with the basics of cosmology and explain the significance of these results and their relevant observational consequences.
Venue: Seminar Room #359 (Main Venue) / via Zoom
Event Official Language: English

Seminar
Surface defect in N=4 SYM and integrability
July 17 (Wed) at 16:00  17:00, 2024
Hiroki Kawai (Ph.D. Student, University of California, Santa Barbara, USA)
In the N=4 super YangMills theory, it is wellknown that the oneloop anomalous dimension operator for the single trace operators is equivalent to an integrable spin chain. Recent works have extended the application of integrability to scenarios involving a BPS boundary or defects such as 't Hooft line. One can describe the correlators of the single trace operators as an overlap between the Bethe state and the corresponding defect state. This overlap can be exactly calculated if the defect state is a socalled integrable state. We show that the state corresponding to the GukovWitten surface defect is integrable. We also calculate the treelevel onepoint function of the single trace operators and set up the perturbation calculation in this defect background for oneloop corrections.
Venue: Hybrid Format (3F #359 and Zoom), Main Research Building
Event Official Language: English

Seminar
Quantum Error Transmutation
July 17 (Wed) at 10:30  11:30, 2024
Daniel Zhang (Postdoctoral Fellow, University of Oxford, UK)
We introduce a generalisation of quantum error correction, relaxing the requirement that a code should identify and correct a set of physical errors on the Hilbert space of a quantum computer exactly, instead allowing recovery up to a prespecified admissible set of errors on the code space. We call these quantum error transmuting codes. They are of particular interest for the simulation of noisy quantum systems, and for use in algorithms inherently robust to errors of a particular character. Necessary and sufficient algebraic conditions on the set of physical and admissible errors for error transmutation are derived, generalising the KnillLaflamme quantum error correction conditions. We demonstrate how some existing codes, including fermionic encodings, have error transmuting properties to interesting classes of admissible errors. Additionally, we report on the existence of some new codes, including lowqubit and translation invariant examples.
Venue: Hybrid Format (3F #359 and Zoom), Seminar Room #359
Event Official Language: English

Seminar
Mapping the Phase Space of toric CalabiYau 3folds using Explainable Machine Learning
July 16 (Tue) at 13:30  14:30, 2024
RakKyeong Seong (Assistant Professor, Department of Mathematical Sciences, Ulsan National Institute of Science and Technology (UNIST), Republic of Korea)
This talk will give a brief introduction on how bipartite graphs on a torus represent 4dimensional quiver gauge theories and their moduli space which is a toric CalabiYau 3fold  a cone over a SasakiEinstein 5manifold. Under mirror symmetry, the bipartite graph can be identified with the tropical projection of the mirror curve obtained from the Newton polytope associated to the toric CalabiYau 3fold. Changes to the complex structure moduli of the mirror CalabiYau determine the overall shape of the bipartite graph on the torus. For certain choices of complex structure moduli, the bipartite graph undergoes a graph mutation which is identified with Seiberg duality of the associated 4dimensional quiver gauge theory. This talk will discuss recent progress in understanding when such mutations occur from the point of view of CalabiYau mirror symmetry with the help of new computational techniques such as machine learning.
Venue: Hybrid Format (3F #359 and Zoom), Seminar Room #359
Event Official Language: English

Seminar
Tensionless Strings in a KalbRamond Background
July 10 (Wed) at 16:00  17:00, 2024
Ritankar Chatterjee (Ph.D. Student, Indian Institute of Technology Kanpur, India)
We investigate tensionless (or null) bosonic string theory with a constant KalbRamond background turned on. In analogy with the tensile case, we find that the constant KalbRamond field has a nontrivial effect on the spectrum only when the theory is compactified on an S^1 ⊗d background with d ≥ 2. We discuss the effect of this constant background field on the tensionless spectrum constructed on three known consistent null string vacua. We elucidate further on the intriguing fate of duality symmetries in these classes of string theories when the background field is turned on. Based on: https://arxiv.org/abs/2404.01385
Venue: Hybrid Format (3F #359 and Zoom), Main Research Building
Event Official Language: English

Worldline Path Integrals for the Graviton and 1Loop Divergences in Quantum Gravity
June 28 (Fri) at 16:00  17:20, 2024
Fiorenzo Bastianelli (Professor, University of Bologna, Italy)
In this talk, I will discuss perturbative quantum gravity at the 1loop level by reviewing and systematizing old results on UV divergences and presenting new findings along with new methods for their calculation. The traditional approach to this problem employs the SchwingerDeWitt heat kernel method. We extend this approach by incorporating worldline path integrals to compute the perturbative expansion at small proper time. In addition, we explore a more principled approach that utilizes the BRST path integral quantization of the N=4 spinning particle, which describes the graviton in first quantization. Using these methods, we calculate the oneloop divergences in quantum gravity with a cosmological constant in arbitrary dimensions. When evaluated onshell, these calculations yield a set of gaugeinvariant coefficients that characterize pure quantum gravity with a cosmological constant. These coefficients may serve as benchmarks for comparing various approaches to quantum gravity.
Venue: Seminar Room #359 (Main Venue) / via Zoom
Event Official Language: English

Magnonic spin current and shot noise in an itinerant Fermi gas
June 25 (Tue) at 13:30  15:00, 2024
Tingyu Zhang (Ph.D. Student, Department of Physics, Graduate School of Science, The University of Tokyo)
Spin transport phenomena at stronglycorrelated interfaces play central roles in fundamental physics as well as spintronic applications. Although the spinflip tunneling process, a key mechanism of spin transport, has been extensively studied in solidstate systems, its behavior in itinerant Fermi gases remains elusive. In this regard we study the spin tunneling in a repulsively interacting ultracold Fermi gas based on the conventional quasiparticle tunneling process. we investigate the spin current induced by quasiparticle and spinflip tunneling processes to see their bias dependence and interaction dependence. To anatomize spin carriers, we propose the detection of the spin current noise in the system. The Fano factor, which is defined as the ratio between the spin current and its noise can serve as a probe of elementary carriers of spin transport. The change of the Fano factor microscopically evinces a crossover from the quasiparticle transport to magnon transport in itinerant fermionic systems.
Venue: Hybrid Format (3F #359 and Zoom), Seminar Room #359
Event Official Language: English

Seminar
Grassmann Tensor Renormalization Group for twoflavor Schwinger model with a theta term
June 24 (Mon) at 16:00  17:00, 2024
Hayato Kanno (Special Postdoctoral Researcher, Theory Group, RIKEN BNL Research Center, RIKEN Nishina Center for AcceleratorBased Science (RNC))
QCD has been understood through numerical calculations by the Monte Carlo method. However, this method does not work for some parameter regions because of the sign problem. For example, QCD with a theta term has a sign problem, so the nature of QCD with a finite theta parameter is unknown. The theta dependence is also important to axion physics. To reveal such systems, tensor network methods are powerful tools. Tensor network methods have been developed by condensed matter theorists. Furthermore, recently there have been some attempts to apply them to high energy physics. In particular, the tensor renormalization group (TRG) method is remarkable for its applicability to higher dimensions. The Schwinger model is known as a twodimensional toy model of QCD. It has the chiral symmetry and theta term as the same as QCD. In this study, the free energy of the twoflavor Schwinger model is calculated in a broad range of mass and theta parameters. We use TRG to calculate it, with obvious 2pi periodicity of theta parameter. We check the consistency with analytical values in large and small mass limits.
Venue: via Zoom / Seminar Room #359
Event Official Language: English

Seminar
Boundaryinduced transitions in Möbius quenches of holographic BCFT
May 15 (Wed) at 16:00  17:30, 2024
Dongsheng Ge (Project Researcher, Department of physics, Osaka University)
Boundary effects play an interesting role in finitesize physical systems. In this work, we study the boundaryinduced properties of 1+1dimensional critical systems driven by inhomogeneous Möbiuslike quenches. We focus on the entanglement entropy in BCFTs with a large central charge and a sparse spectrum of lowdimensional operators. We find that the choice of boundary conditions leads to different scenarios of dynamical phase transitions. We also derive these results in a holographic description in terms of intersecting branes in AdS3, and find a precise match.
Venue: Seminar Room #359 (Main Venue) / via Zoom
Event Official Language: English

Seminar
Role of selfgravity on the central halo structure of fuzzy dark matter
April 30 (Tue) at 13:30  15:00, 2024
Yusuke Manita (Affiliated Scientist, Yukawa Institute for Theoretical Physics, Kyoto University)
Fuzzy dark matter (FDM) is a dark matter model that is characterized by the ultralight masses around 10−22 eV. As FDM has the wavelike nature, the selfgravitating structure is described by the SchrödingerPoisson equation. Previous simulations based on the SchrödingerPoisson equation have demonstrated that solitonlike structure having a highdensity flat core is formed at the central region of the FDM halos, and the size of such a core is typically determined by the de Broglie wavelength. Away from the central core, the density profile of the FDM halos resembles that of the cold dark matter halos on average, and is shown to be described by the NavarroFrenkWhite (NFW) profile. In this paper, we study the role of the selfgravity of the soliton core, and its relation to the bulk halo properties by solving the SchrödingerPoisson equation in a simplified setup. The findings indicate that the contribution from the soliton selfgravity must dominate over the NFW potential in order to sustain the soliton.
Venue: Hybrid Format (3F #359 and Zoom), Main Research Building
Event Official Language: English

Seminar
A night out with ghosts
April 24 (Wed) at 16:00  17:30, 2024
Veronica Errasti Diez (Research Fellow, Faculty of Physics, LudwigMaximiliansUniversität München, Germany)
Field theories are the chief theoretical framework for physics. For instance, the Standard Model and General Relativity are widely accepted as accounting for subatomic particle and gravitational behavior, respectively. Nonetheless, even such acclaimed field theories have their limitations, such as the mysterious neutrino masses and dark sector. A natural and popular way around the hurdles consists in generalizations of field theories, via the inclusion of nonlinear and/or higherorder corrections. Unless painstakingly avoided, these corrections lead to the propagation of negative kinetic energy modes, or ghosts for short. Ghosts have earned an appalling fame: kill, exorcise, avoid… No efforts are spared to guarantee their absence. In this talk, we will delve into the root causes for the ill name of ghosts. As a result, we will take up the cudgels for ghosts. While they do have a strong tendency to yield illbehaved theories, ghosts are not intrinsically pathological. As we will see, goodnatured ghosts open the door to multidisciplinary tantalizing opportunities…! And ghosts make excellent partygoers, so make sure not to miss this appointment!
Venue: Hybrid Format (3F #359 and Zoom), Main Research Building
Event Official Language: English

Seminar
ShortLived Hawking Radiation Under Stringy Effects
April 11 (Thu) at 13:30  15:00, 2024
WeiHsiang Shao (Ph.D. Student, Department of Physics, National Taiwan University, Taiwan)
A UV theory is required in order to describe the origin of latetime Hawking radiation. In this talk, I will explore Hawking radiation in a nonlocal model of the radiation field inspired by Witten's open string field theory. An attempt at extracting the correlators of this theory will be discussed, which leads to a spacetime uncertainty relation. As a result, the characteristics of transPlanckian field modes differ significantly from that in the standard lowenergy effective theory, and I will argue that this ultimately results in the termination of Hawking radiation around the scrambling time of the black hole.
Venue: Hybrid Format (3F #359 and Zoom), Main Research Building
Event Official Language: English

Seminar
Brane field theory with higherform symmetry
March 12 (Tue) at 14:00  15:30, 2024
Kiyoharu Kawana (Research Fellow, Korea Institute for Advanced Study (KIAS), Republic of Korea)
We propose field theory for branes with higherform symmetry as a generalization of ordinary Landau theory. The field \psi[C_p^{}] becomes a functional of pdimensional closed brane Cp embedded in a spacetime. As a natural generalization of ordinary field theory, we call this theory brane field theory. In order to construct an action that is invariant under higherform transformation, we first generalize the concept of “derivative” for higherdimensional objects. Then, we discuss various fundamental properties of the brane field based on the higherform invariant action. It is shown that the classical solution exhibits the area law in the unbroken phase of U(1) pform symmetry, while it indicates a constant behavior in the broken phase for the large volume limit of Cp. In the latter case, the lowenergy effective theory is described by the pform Maxwell theory. If time permits, we also discuss branefield theories with a discrete higherform symmetry and show that the lowenergy effective theory becomes a BFtype topological field theory, resulting in topological order.
Venue: Hybrid Format (3F #359 and Zoom), Main Research Building
Event Official Language: English

Seminar
Stochastic tunneling in de Sitter spacetime
February 28 (Wed) at 16:00  17:30, 2024
Taiga Miyachi (Ph.D. Student, Institute of Cosmophysics, Department of Physics, Graduate School of Science, Kobe University)
The formulation of tunneling in real time formalism is discussed. In the case of de Sitter spacetime, there is a method called the stochastic approach, which is known to reproduce the tunneling predicted by Hawking and Moss in the imaginary time formalism. In the case of accelerated expansion of space, the shortwavelength modes are stretched and transformed into longwavelength modes. In the stochastic approach, such UVIR transition is incorporated as quantum noise, and the dynamics of the longwavelength modes are described by stochastic differential equations. In this talk, we construct a SchwingerKeldysh path integral that reproduces this stochastic differential equation and reformulate the tunneling probability. We also reproduce the HawkingMoss tunneling probabilities by using the saddle point approximation.
Venue: Seminar Room #359 (Main Venue) / via Zoom
Event Official Language: English

Seminar
Recent advances in nuclear Density Functional Theory and applications to the nuclear response
February 6 (Tue) at 13:30  15:00, 2024
Gianluca Colò (Professor, Department of Physics, University of Milan, Italy / Professor, Sezione di Milano, INFN, Italy)
In this contribution, I will give an overall (and, of course, biased) view of the general status of DFT. I will stress that, in contrast to ab initio methods, DFT is the only framework that allows the study of excited states, including those lying at relatively high energy. Accordingly, I will focus on the nuclear response. After a reminder on the nuclear Giant Resonances and the link with the nuclear equation of state, I will discuss the projection methods to restore symmetries in the calculations of deformed systems. While symmetryrestored calculations are nowadays of common use in the study of groundstate properties and lowlying excitations, similar realistic investigations for the nuclear response are essentially missing in the literature. Recently, we have implemented an exact Angular Momentum Projection (AMP) on top of SkyrmeRandom Phase Approximation (RPA) calculations in a projection after variation (PAV) scheme, for the first time. The results will be critically analysed in the case of the monopole response, also taking into account the experimental investigations that can be envisioned for welldeformed systems. If time allows, the nuclear response will be also discussed as a way to improve the current density functionals and ground them on ab initio nuclear theory. This seminar is cohosted by Nuclear Manybody Theory Laboratory and Fewbody Systems in Physics Laboratory, RIKEN Nishina Center for AcceleratorBased Science.
Venue: 2F Large Meeting Room, RIBF Building, RIKEN Wako Campus (Main Venue) / via Zoom
Event Official Language: English

Seminar
Nuclear EnergyDensity Functional Approach to Bridging NeutronRich Nuclei and Neutron Stars
February 5 (Mon) at 13:30  15:00, 2024
Kenichi Yoshida (Associate Professor, Research Center for Nuclear Physics, Osaka University)
Understanding the properties of neutronrich nuclei has been a central subject in lowenergy nuclear physics. The great interest lies not only in the pursuit of a variety of structures and the elucidation of the mechanisms of their occurrence but also in obtaining insights into the structure of the inner crust of neutron stars. With advances in neutronstar observation techniques, the structure of neutron stars has been becoming better understood. The data accumulated from these observations unveil properties of neutronrich matter that are otherwise inaccessible through terrestrial experiments. In this talk, I will introduce an attempt to construct a nuclear energydensity functional (EDF) inspired by the observations and then demonstrate its applicability to nuclear structure problems, including mass and deformation. One intriguing aspect of neutron stars is the emergence of superfluidity, especially the occurrence of spintriplet pairing. I will discuss the unconventional pairing in nuclei within the nuclear EDF framework and give perspectives on the study of the phase diagram of the superfluidity in neutron stars. This seminar is cohosted by UKAKUREN.
Venue: Seminar Room #359 (Main Venue) / via Zoom
Event Official Language: English

Quantum features in cosmological perturbations?
January 18 (Thu) at 14:15  15:00, 2024
Amaury Micheli (Postdoctoral Researcher, iTHEMS)
The statistical properties of the CMB anisotropies, reflecting the curvature inhomogeneities in the very early Universe, are very well accounted for by assuming that the inhomogeneities come from amplified vacuum fluctuations. This scenario makes the cosmological perturbations a possible observational window on the interplay between quantum degrees of freedom and gravity. I will review the discussions on the current presence or absence of quantum features in the perturbations, emphasising the quantum information approaches to this question, and comment on the observability of these features.
Venue: Hybrid Format (3F #359 and Zoom), Main Research Building
Event Official Language: English

Seminar
Gravitational lensing on superposed curved spacetime
January 18 (Thu) at 13:30  14:15, 2024
Youka Kaku (Ph.D. Student, Graduate School of Science, Nagoya University)
In 2017, Bose et al. proposed a tabletop experiment to observe the gravitational effect induced by a spatially superposed mass source, particularly gravityinduced entanglement. This experiment is expected to be the first step in exploring the quantum nature of gravity. Also, there are ongoing efforts to extend their proposal to the relativistic region to observe the unique quantum nature of gravity. In this talk, I will investigate gravitational lensing in a weak gravitational field induced by a spatially superposed mass source. I will show the Einstein ring image of a quantum scalar field propagated on a superposed curved spacetime and compare it with the image of the semiclassical gravity case. This work is currently in progress and is a collaboration with Yasusada Nambu.
Venue: Hybrid Format (3F #359 and Zoom), Main Research Building
Event Official Language: English

Seminar
Symmetry Topological field theory for Subsystem symmetry
January 9 (Tue) at 15:00  16:00, 2024
Qiang Jia (Research Fellow, School of Physics, Korea Institute for Advanced Study (KIAS), Republic of Korea)
We generalize the idea of symmetry topological field theory (SymTFT) to subsystem symmetry. We propose the 2foliated BF theory with level N in (3+1)d as subsystem SymTFT for subsystem Z_N symmetry in (2+1)d. Focusing on N=2, we investigate various topological boundaries. The subsystem KramersWannier and JordanWigner dualities can be viewed as boundary transformations of the subsystem SymTFT and are included in a larger duality web from the subsystem SL(2,Z_2) symmetry of the bulk foliated BF theory.
Venue: via Zoom / Seminar Room #359
Event Official Language: English
76 events
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