Seminar
603 events

Probing structure of neutron stars through Xray bursters
January 12 (Fri) at 14:00  15:15, 2024
Akira Dohi (Special Postdoctoral Researcher, Astrophysical Big Bang Laboratory, RIKEN Cluster for Pioneering Research (CPR))
TypeI Xray bursts are rapidly brightening phenomena triggered by the nuclear burning of light elements near the surface of accreting neutron stars. Most of the Xray bursters show irregular behavior of light curves. However, some Xray bursters are somehow quite regular, i.e., constant recurrence time and constant shaper of light curves, and are often called Clocked bursters, which are powerful sites to probe uncertainties of many model parameters such as accretion rate, the composition of accreted matter, reaction rates, neutron star structure, and temperature. In this study, we focus on the uncertainties of the equation of states, which determines the latter two properties. Based on our numerical models covering whole areas of neutron stars, we will present their impact on Xray burst light curves. Furthermore, we will discuss the possibility of constraining the equation of states from Clocked bursters such as GS 182624 and 1RXS J180408.9342058.
Venue: Seminar Room #359 (Main Venue) / via Zoom
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

Seminar
Application of Modular tensor category to Lattice gauge theory
December 29 (Fri) at 10:30  16:00, 2023
Tomoya Hayata (Assistant Professor, Faculty of Economics, Keio University)
Inspired by the recent development in quantum computers, much efforts have been devoted to exploring their potential applications in lattice gauge theories. However, in contrast to condensed matter systems, we face many challenges in applications of quantum computations to lattice gauge theories, where one of the major obstructions lies in implementation of gauge symmetries in quantum computations. In this seminar, I talk about a possible solution to the problem based on a unitary modular tensor category, expressing the Hamiltonian of lattice gauge theories in terms of the so called F moves, and implementing the F moves on quantum computers. References: TH, Y. Hidaka, JHEP 09 (2023) 126; JHEP 09 (2023) 123.
Venue: Seminar Room #359
Event Official Language: English

Seminar
Oscillatory data analysis using the extended Hilbert transform method
December 26 (Tue) at 16:00  17:00, 2023
Akari Matsuki (Postdoctoral Researcher, Department of Advanced Transdisciplinary Sciences, Hokkaido University)
Oscillatory phenomena are observed in various biological systems, such as spinal nervous systems and circadian rhythms. These macroscopic oscillatory phenomena appear as a result of synchronization of microscopic oscillators, such as pacemaker cells. The first step in the analysis of synchronization is to reconstruct the "phase" from the observed signal. The Hilbert transform method is one of the popular methods for phase reconstruction, but it is known that it can only accurately reconstruct the phase from a limited class of signals such as narrowband signals. In this study, we show that the Hilbert transform method has a lowpass filterlike effect on the phase modulation and propose an "extended Hilbert transform method" that can be applied to a wider class of signals. In this talk, I will introduce the extended Hilbert transform method, and its application to phase shift detection and coupling network inference.
Venue: via Zoom
Event Official Language: English

A symmetry principle for gauge theories with fractons
December 22 (Fri) at 17:00  18:15, 2023
Yuji Hirono (ProgramSpecific Associate Professor, Department of Physics, Division of Physics and Astronomy, Graduate School of Science, Kyoto University)
Fractonic phases are emergent quantum phases of matter that host excitations with restricted mobility. Although these phases have been considered to be of “beyond Landau” order, we show that a certain class of gapless fractonic phases are realized as a result of spontaneous breaking of generalized symmetries. The corresponding symmetries are continuous higherform symmetries whose conserved charges do not commute with spatial translations, and we refer to them as nonuniform higherform symmetries. For a given set of nonuniform symmetries, the effective theory associated with the spontaneous breaking of them can be constructed. At low energies, the theories reduce to known higherrank gauge theories such as scalar/vector charge gauge theories, and the gapless excitations in these theories are interpreted as Nambu–Goldstone modes for higherform symmetries. Due to the nonuniformity of the symmetry, some of the modes acquire a gap, which is the higherform analogue of the inverse Higgs mechanism of spacetime symmetries. In this formulation, the mobility restrictions are fully determined by the choice of the commutation relations of charges with translations. This approach allows us to view existing (gapless) fracton models such as the scalar/vector charge gauge theories and their variants from a unified perspective and enables us to engineer theories with desired mobility restrictions. Field: condensed matter physics Keywords: fractonic phases, higherform symmetries, NambuGoldstone modes, Higgs mechanism, gauge theories
Venue: via Zoom
Event Official Language: English

Seminar
Inflationary Cosmology with a scalarcurvature mixing term $\frac{1}{2} \xi R \phi^2$
December 20 (Wed) at 16:00  17:30, 2023
Payel Sarkar (Visiting Researcher, Kyoto University)
We use the PLANCK 2018 and the WMAP data to constraint inflation models driven by a scalar field $\phi$ in the presence of the nonminimal scalarcurvature mixing term $\frac{1}{2}\xi R \phi^2$. We consider four distinct scalar field potentials $\phi^p e^{\lambda\phi},~(1  \phi^{p})e^{\lambda\phi},~(1\lambda\phi)^p$ and $\frac{\alpha\phi^2}{1+\alpha\phi^2}$ to study inflation in the nonminimal gravity theory. We calculate the potential slowroll parameters, predict the scalar spectral index $n_s$, tensortoscalar ratio $r$, leading and higher order nonGaussianity parameters ($f_{NL},~\tau_{NL}$ and $g_{NL}$) and the amplitude of the scalar spectrum $A_s$ in the parameter ($\lambda, p, \alpha$) space of the potentials corresponding to different values of the nonminimal coupling parameter $\xi$. We have compared our results with the ones existing in the literature, and this indicates the present status of nonminimal inflation after the release of the PLANCK 2018 data.
Venue: Hybrid Format (3F #359 and Zoom), Main Research Building (Main Venue) / via Zoom
Event Official Language: English

Application of mathematical models to the COVID19 cohort study
December 19 (Tue) at 16:00  17:00, 2023
Takara Nishiyama (Ph.D. Student, Graduate School of Science, Nagoya University)
The COVID19 pandemic, which began in 2019, has caused widespread morbidity and mortality across the globe. In response, a multitude of studies focusing on SARSCoV2 have been undertaken. Among these, cohort studies have been particularly significant. These studies, as a key observational research method, play a crucial role in exploring the links between various factors and the onset of diseases, offering valuable insights for disease control. Mathematical model, applied within these studies, provide essential quantitative data. In my talk, I will introduce how mathematical models are instrumental in cohort studies, drawing on two of my own COVID19 cohort studies as examples.
Venue: Hybrid Format (3F #359 and Zoom), Main Research Building
Event Official Language: English

Seminar
Energy spectrum and time evolution of a SU(2) pure gauge lattice theory on a quantum annealer
December 18 (Mon) at 14:00  15:00, 2023
Emanuele Mendicelli (Postdoctoral Research Associate, Department of Mathematical Sciences, University of Liverpool, UK)
Lattice gauge theory is an indispensable tool for nonAbelian fields, such as those in quantum chromodynamics where lattice results have been of central importance for several decades. Recent studies suggest that quantum hardware could extend the reach of lattice gauge theory to inaccessible phenomena due to the need for an exponentially large amount of resources, the socalled sign problem. Among the available quantum hardware gatebased quantum computer are well know but less common quantum annealer can play a role too. In this talk we briefly report one of the first use of DWave quantum annealer to study the energy spectrum and the time evolution of a SU(2) pure gauge lattice theory in its Hamiltonian formulation. In particular we present how to extract the energy spectrum using the quantum Quantum Annealer Eigensolver algorithm and perform the time evolution using the KitaevFeynman clock states. Despite the nosy hardware, no error mitigation techniques were needed but the usability of the DWave hardware was extended by simply blockdiagonalizing the Hamiltonian.
Venue: Seminar Room #359 (Main Venue) / via Zoom
Event Official Language: English

Seminar
Plasticity in the endogenous rhythms and the adaptation to the tidal environment in a freshwater snail
December 14 (Thu) at 16:00  17:00, 2023
Takumi Yokomizo (JSPS Research Fellow PD, Graduate School of Science, Chiba University)
Organisms have diverse biological clocks synchronized with environmental cycles depending on their habitats. The change in endogenous rhythms could contribute to range expansion in a novel rhythmic environment. For example, the Anticipation of tidal changes has driven the evolution of circatidal rhythms in some marine species. I am interested in the genetic and nongenetic changes in the biological rhythms and adaptation to tidal environments in the freshwater snail, Semisulcospira reiniana. Chronobiological analyses of behavior and gene expression revealed that snails had habitatspecific endogenous rhythms: individuals in a nontidal population showed the circadian rhythm while those in a tidal population showed the circadian and circatidal rhythms. The entrainment to the simulated tidal cycles increased the strength of circatidal activity only in snails in a tidal population. Although the circatidal rhythms in the transcriptome were clearer in individuals entrained to tidal cycles, the number of circatidal rhythmic transcripts was greater in a tidal population than in a nontidal population. These results suggest biological rhythms in the snails plastically change at the molecular level, but the strength of circatidal rhythm is different between populations. Finally, transcriptomewide population genetic analysis revealed that these two populations can be clearly distinguished genetically, though the genetic distance was very small. Thus, genetic differentiation in biological rhythms could result from the evolution of a small number of genes. These findings suggest that adaptive plasticity and genetic changes in the biological rhythms play an important role in coping with tidal environments.
Venue: via Zoom
Event Official Language: English

Tropical geometry and period integrals
December 13 (Wed) at 14:00  16:30, 2023
Yuto Yamamoto (Special Postdoctoral Researcher, iTHEMS)
Tropical geometry is a field of mathematics that naturally emerges when considering the limits of spaces with respect to some parameters. One of the motivations to study tropical geometry is to describe the behaviors of the spaces under the limit. In this math seminar, starting with a brief introduction to tropical geometry, we discuss its application to computation of period integrals, which are one of the most fundamental quantities of complex manifolds. The goal is to compute asymtptotics of period integrals for complex hypersurfaces in toric varieties using tropical geometry, and observe that the Riemann zeta values (or the gamma classes) appear in the result of the computation. The first half of the talk will be a brief introduction to tropical geometry for nonexperts including those who are working outside mathematics, and everyone will be welcome.
Venue: Hybrid Format (3F #359 and Zoom), Main Research Building
Event Official Language: English

Exploring material strengths of dust aggregates in planet formation by numerical simulations
December 8 (Fri) at 14:00  15:15, 2023
Misako Tatsuuma (Research Scientist, iTHEMS)
The planet formation process is the growth from submicrometersized cosmic dust grains to thousandkilometersized planets. This growth process has broadly two phases: the growth from dust grains to kilometersized planetesimals, mainly driven by intermolecular forces like van der Waals forces and hydrogen bonds, and the subsequent growth from planetesimals to planets, governed by gravitational forces. However, the planetesimal formation process encounters various challenges, including fragmentation and bouncing resulting from collisions among dust aggregates. To gain insights into the planetesimal formation process and how to avoid these obstacles, I have been focused on measuring and formulating the material strengths of dust aggregates using grain simulations. In this talk, I will introduce my works on the material strengths of dust aggregates and their applications to kilometersized bodies in the solar system, such as comets and asteroids.
Venue: Seminar Room #359 (Main Venue) / via Zoom
Event Official Language: English

Seminar
Gravitational Lensing in Black Hole Spacetimes of the PlebanskiDemianski Class
December 6 (Wed) at 16:00  17:30, 2023
Torben Christian Frost (Postdoctoral Researcher, Kavli Institute for Astronomy and Astrophysics, Peking University, China)
Einstein's field equations allow various different black hole solutions. Among these solutions, the most famous are most likely the Schwarzschild and the Kerr spacetimes, which are both special cases of the socalled PlebanskiDemianski spacetime. Besides the Schwarzschild and Kerr spacetimes, the PlebanskiDemianski spacetime also includes other solutions as special cases, among them the Cmetric and the NUT metric. They describe a linearly accelerating black hole and a black hole with gravitomagnetic charge, respectively. The question is now how we can determine if an astrophysical black hole can be described by one of these spacetimes. We will address this question using gravitational lensing for the three spacetimes with the most salient lensing features, namely the Cmetric, the NUT metric, and the Kerr metric. For this purpose, we will first outline how to solve the equations of motion analytically using elementary and Jacobi's elliptic functions as well as Legendre's elliptic integrals. Then we will fix an observer in the domain of outer communication and relate the constants of motion of the lightlike geodesics to latitudelongitude coordinates on the observer's celestial sphere. We will use the analytic solutions to write down the lens equations, calculate the redshift, and the travel time. Finally, we will discuss and compare the results and comment on how we can use them to place constraints on the spin parameter, the acceleration parameter, and the gravitomagnetic charge of a black hole.
Venue: Seminar Room #359 (Main Venue) / via Zoom
Event Official Language: English

Seminar
Cosection localization via shifted symplectic geometry
December 6 (Wed) at 10:00  11:30, 2023
YoungHoon Kiem (Professor, School of Mathematics, Korea Institute for Advanced Study (KIAS), Republic of Korea)
Modern enumerative invariants are defined as integrals of cohomology classes against virtual fundamental classes constructed by LiTian and BehrendFantechi. When the obstruction sheaf admits a cosection, the virtual fundamental class is localized to the zero locus of the cosection. When the cosection is furthermore enhanced to a (1)shifted closed 1form, the zero locus admits a (2)shifted symplectic structure and thus we have another virtual fundamental class by the OhThomas construction. An obvious question is whether these two virtual fundamental classes coincide or not. In this talk, we will see that (1)shifted closed 1forms arise naturally as an analogue of the Lagrange multiplier method. Furthermore, a proof of the equality of the two virtual fundamental classes and its applications will be discussed. Based on a joint work with Hyeonjun Park.
Venue: Seminar Room #359
Event Official Language: English

Translating between evolutionary game theory and theoretical ecology
December 5 (Tue) at 16:30  17:30, 2023
Arne Traulsen (Director, Department for Theoretical Biology, Max Planck Institute for Evolutionary Biology, Germany)
Both theoretical ecology and evolutionary game theory describe the dynamics of interacting populations. More than 40 years ago, Hofbauer and Sigmund established a mathematical equivalence between the LotkaVolterra equations and the replicator dynamics from evolutionary game theory. However, this equivalence has not been exploited by empiricists so far. One of the issues is dimensionality: An ecological interaction of two species corresponds to an evolutionary game between three types. Only when we focus on a special case with identical growth rates, it is possible to translate without this trick, leading to a more direct equivalence between the frameworks. Consequently, one has to be particularly careful how to classify interactions and how to assess dynamical outcomes. For example, a ‘Prisoner's Dilemma’ interaction where the `cooperators' have a higher intrinsic growth rate than `defectors' can result in stable coexistence of the two types and may ultimately not represent a social dilemma at all.
Venue: via Zoom
Event Official Language: English

Seminar
Rotating discs on the Kerr black hole background
December 5 (Tue) at 15:00  16:30, 2023
David Kofroň (Postdoctoral Researcher, Institute of Theoretical Physics, Charles University, Czechia)
Analytical solution of a rotating black hole surrounded by accretion disc in full GR is, so far, unknown. The Ernst equation is nonlinear. In this talk, we will provide a framework in which the solutions of linearised Ernst equations can be obtained from the linear perturbations of Kerr black hole treated in the formalism of the Debye potentials. In this way, we recover all the metric perturbations in term of a single complex scalar function (which solves the Laplace equation).
Venue: Seminar Room #359 (Main Venue) / via Zoom
Event Official Language: English

Seminar
Gravity of Accretion Discs and Black Holes
December 5 (Tue) at 14:00  15:00, 2023
Petr Kotlařík (Ph.D. Student, Institute of Theoretical Physics, Charles University, Czechia)
The typical black hole solutions describe only isolated black holes. However, in astrophysics, such a condition is never strictly satisfied. As matter accretes onto the black hole, disc structures are often formed. In this talk, I will summarize our recent attempts to find the gravitational field of such a nonisolated black hole. We start from the simplest case of static and axially symmetric metric. Although it is a somewhat "rough" approximation in the astrophysical context, this idealization may already help us to understand some interesting implications of the disc's gravity. Moreover, with such a simplification, we can obtain exact analytical "superpositions" of the Schwarzchild black hole and a disc. When some rotation is present, dragging effects complicate the situation dramatically. Then, one typically has to resort to numerical relativity or some approximate methods, e.g., perturbations. In the talk, I also address the stationary case and demonstrate what we can do on the level of the direct metric perturbation.
Venue: Seminar Room #359 (Main Venue) / via Zoom
Event Official Language: English

Seminar
Breaking down the magnonic WiedemannFranz law in the hydrodynamic regime
December 4 (Mon) at 15:00  16:30, 2023
Ryotaro Sano (Ph.D. Student, Division of Physics and Astronomy, Graduate School of Science, Kyoto University)
Quantum transport has attracted a profound growth of interest owing to its fundamental importance and many applications in condensed matter physics. Recent significant developments in experimental techniques have further boosted the study of quantum transport. Notably in ultraclean systems, strong interactions between quasiparticles drastically affect the transport properties, resulting in an emergent hydrodynamic behavior. Recent experiments on ultrapure ferromagnetic insulators have opened up new pathways for magnon hydrodynamics. Hydrodynamic magnon transport implies exhibiting extraordinary features and has a potential for innovative functionalities beyond the conventional noninteracting magnon picture. However, the direct observation of magnon fluids remains an open issue due to the lack of probes to access the time and length scales characteristics of this regime. In this work, we derive a set of coupled hydrodynamic equations for a magnon fluid and study the spin and thermal conductivities by focusing on the most dominant time scales [1]. As a hallmark of the hydrodynamic regime, we reveal that the ratio between the two conductivities shows a large deviation from the socalled magnonic WF law. We also identify an origin of the drastic breakdown of the magnonic WF law as the difference in relaxation processes between spin and heat currents, which is unique to the hydrodynamic regime. Therefore, our results will become key evidence for an emergent hydrodynamic magnon behavior and lead to the direct observation of magnon fluids.
Venue: Hybrid Format (3F #359 and Zoom), Main Research Building
Event Official Language: English

Evolution by gene and genome duplications
November 28 (Tue) at 16:00  17:00, 2023
Jeffrey Fawcett (Senior Research Scientist, iTHEMS)
Each organism typically has (tens of) thousands of genes in its genome that perform various molecular and cellular functions, but how did these genes originate? The answer for most genes is by the duplication of another gene. In fact, all the genes (the entire genome) can get duplicated simultaneously on some instances. Thus, gene and genome duplications are considered key driving forces of evolution and are one of the most important topics in molecular evolutionary biology. In this talk, I will introduce the background and basic concepts related to gene and genome duplications. The talk will be aimed at nonexperts so nonbiologists are also welcome to attend.
Venue: via Zoom
Event Official Language: English

Early Formation of Dark Matter Halos
November 24 (Fri) at 14:00  15:15, 2023
Derek Beattie Inman (Research Scientist, iTHEMS)
Cosmological observations have led to an extremely precise understanding of the largescale structure of the Universe. A common assumption is to extrapolate largescale properties to smaller scales; however, whether this is correct or not is unknown and many wellmotivated early Universe scenarios predict substantially different structure formation histories. In this seminar I will discuss two scenarios where nonlinear structures form much earlier than is typically assumed. In the first case, the initial fluctuations are enhanced on small scales leading to either primordial black holes clusters or WIMP minihalos right after matterradiation equality. In the second, I will show that an additional attractive dark force leads to structure formation even in the radiation dominated Universe. I will furthermore discuss possible observations of such early structure formation including changes to the cosmic microwave background, dark matter annihilation, and when the first galaxies form.
Venue: Seminar Room #359 (Main Venue) / via Zoom
Event Official Language: English

Seminar
Volume complexity of de Sitter bubbles
November 22 (Wed) at 16:00  17:30, 2023
Nicolò Zenoni (Project Researcher, Department of Physics, Osaka University)
Holographic complexity is conjectured to probe the evolution of spacetime. For black holes in antide Sitter (AdS) spacetime the growth rate of complexity approaches a constant value at late times, while in de Sitter (dS) spacetime it diverges at a finite critical time. In this talk, we consider geometries interpolating between AdS and dS. In particular, we discuss the evolution of volume complexity in a class of threedimensional asymptotically antide Sitter geometries including dynamical bubbles of de Sitter in their interior. According to the dynamics of the bubble, complexity qualitatively behaves either as in the AdS black hole or as in the dS case. We conclude with some remarks about the possible dual interpretation.
Venue: Seminar Room #359 (Main Venue) / via Zoom
Event Official Language: English
603 events
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