iTHEMS Seminar
24 events
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Seminar
Hopfions in Condensed Matter and Field Theory
December 16 (Mon) at 16:00 - 17:30, 2024
Avadh Saxena (Professor, Los Alamos National Laboratory, USA)
Abstract: Nontrivial topological defects such as knotted solitons called hopfions have been observed in a variety of materials including chiral magnets, nematic liquid crystals and even in ferroelectrics as well as studied in other physical contexts such as Bose-Einstein condensates. These topological entities can be modeled using the relevant physical variable, e.g., magnetization, polarization or the director field. Specifically, we find exact static soliton solutions for the unit spin vector field of an inhomogeneous, anisotropic three-dimensional (3D) Heisenberg ferromagnet and calculate the corresponding Hopf invariant H analytically and obtain an integer, demonstrating that these solitons are indeed hopfions [1]. H is a product of two integers, the first being the usual winding number of a skyrmion in two dimensions, while the second encodes the periodicity in the third dimension. We also study the underlying geometry of H, by mapping the 3D unit vector field to tangent vectors of three appropriately defined space curves. Our analysis shows that a certain intrinsic twist is necessary to yield a nontrivial topological invariant: linking number [2]. Finally, we focus on the formation energy of hopfions to study their properties for potential applications. Short bio: Avadh Saxena is former Group Leader of the Condensed Matter and Complex Systems group (T-4) at Los Alamos National Lab, New Mexico, USA where he has been since 1990. He is also an affiliate of the Center for Nonlinear Studies at Los Alamos. His main research interests include phase transitions, optical, electronic, vibrational, transport and magnetic properties of functional materials, device physics, soft condensed matter, non-Hermitian quantum mechanics, geometry, topology and nonlinear phenomena & materials harboring topological defects such as solitons, polarons, excitons, breathers, skyrmions and hopfions. He recently completed a book on “Phase Transitions from a Materials Perspective” (Cambridge University Press, 2024). He is an Affiliate Professor at the Royal Institute of Technology (KTH), Stockholm, Sweden and holds adjunct professor positions at the University of Barcelona, Spain, University of Crete, Greece, Virginia Tech and the University of Arizona, Tucson. He is Scientific Advisor to National Institute for Materials Science (NIMS), Tsukuba, Japan. He is a Fellow of Los Alamos National Lab, a Fellow of the American Physical Society (APS), a Fellow of the Japan Society for the Promotion of Science (JSPS) and a member of the Sigma Xi Scientific Research Society, APS and American Ceramic Society (ACerS).
Venue: Hybrid Format (3F #359 and Zoom), Seminar Room #359
Event Official Language: English
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Seminar
Studying quark-gluon plasma with multi-stage dynamical models in relativistic nuclear collisions
December 10 (Tue) at 15:30 - 17:00, 2024
Yuuka Kanakubo (Postdoctoral Researcher, iTHEMS)
A collision of relativistically accelerated large nuclei creates the hottest matter on Earth — quark-gluon plasma (QGP). The properties of QGP have been studied through comparisons of final-state particle distributions between theoretical models and experimental data. To quantitatively constrain QGP properties, it is necessary to build Monte Carlo models that simulate the space-time evolution of the system throughout the entire collision process. This includes the initial matter production from the accelerated nuclei, the evolution of QGP, hadronisation, and the evolution of hadron gas. In this talk, I will first explain how theoretical models, based on relativistic hydrodynamics and hadronic transport, are conventionally built and how they successfully extract QGP properties. Next, I will discuss a hot topic: the possibility of finding QGP in proton-proton collisions, based on results from a state-of-the-art model that includes both equilibrated and non-equilibrated systems. Also, I will introduce a novel Monte Carlo initial state model based on perturbative QCD minijet production supplemented with a saturation picture. This Monte-Carlo EKRT model is one of the first initial state models for hydrodynamics to describe initial particle production from small to large momentum within a single framework, where total energy-momentum and charge conservations are imposed.
Venue: #359 3F, Seminar Room #359 (Main Venue) / via Zoom
Event Official Language: English
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Seminar
Entanglement of astrophysical neutrinos
December 10 (Tue) at 13:30 - 15:00, 2024
Baha Balantekin (Eugene P. Wigner Professor, Department of Physics, University of Wisconsin-Madison, USA)
Collective oscillations of neutrinos represent emergent nonlinear flavor evolution phenomena instigated by neutrino-neutrino interactions in astrophysical environments with sufficiently high neutrino densities. In this talk, after a brief introduction, it will be shown that neutrinos exhibit interesting entanglement behavior in simplified models of those oscillations. Attempts to study this behavior using classical and quantum computers will be described. An intriguing connection to the heavy-element nucleosynthesis, namely the possibility of neutrino entanglement driving a new kind of i-process nucleosynthesis, will be introduced,
Venue: Hybrid Format (3F #359 and Zoom), Seminar Room #359
Event Official Language: English
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Seminar
Crop domestication
November 25 (Mon) at 15:00 - 17:00, 2024
Cheng-Ruei Lee (Professor, Institute of Ecology and Evolutionary Biology, National Taiwan University, Taiwan)
Jeffrey Fawcett (Senior Research Scientist, iTHEMS)This is a joint seminar hosted by the Mathematical Biology lab of Kyushu University where Jeffrey Fawcett (iTHEMS) and Cheng-Ruei Lee (National Taiwan University) will give talks about plant domestication. Both talks will be aimed at students and will include some basic introduction of the topic. The seminar will be held on-site at Kyushu University and also by zoom so please free to register and join. Program: Title: Domestication and dispersal process of common buckwheat Speaker: Dr. Jeffrey Fawcett (RIKEN iTHEMS) Abstract: Crop domestication has not only been an ideal model to study how selection drives evolution, it is also tightly linked to past human activity and contains useful information that can improve plant breeding. Common buckwheat (Fagopyrum esculentum), which is used to make “soba” noodles in Japan, was domesticated from a wild progenitor species distributed in Southwest China. We have been using whole-genome sequences of several hundred cultivated accessions from around the world and some wild progenitor accessions to study its process of domestication and subsequent dispersal throughout Eurasia including Japan. In this talk, I will first provide an overview of the domestication and dispersal process of common buckwheat based on archaeological findings. I will then discuss the domestication and dispersal process and adaptive evolution of common buckwheat based on results of our population genetic analyses [1]. Title: The domestication and expansion history of mung bean and adzuki bean: evidence from population genomics Speaker: Prof. Cheng-Ruei Lee (National Taiwan University) Abstract: Who domesticated the crops we eat? When and where? What happened after domestication? How did crops spread across the world? These are the questions that have fascinated archaeologists for a long time. Using modern genomics techniques, we aim to answer these questions from a different angle. In mung bean (Vigna radiata), we uncovered a unique route of post-domestication range expansion. This route cannot be explained simply by human activities alone; instead, it is highly associated with the natural climates across Asia. We showed how the trans-continental climatic variability affected the range expansion of a crop and further influenced local agricultural practices and the agronomic properties of mung bean varieties. In adzuki (Vigna angularis), we obtained solid evidence of its domestication in Japan, most likely by the Jomons. We identified and validated the causal mutations for the seed coat color change during domestication. Contrary to the common belief that important yield-ensuring phenotypes (e.g., loss of pod shattering) should be selected early during domestication, we revealed a unique order of domestication trait evolution that cannot be observed from archaeological records directly [2]. Please register via the form by November 22nd (Fri.). We will share the Zoom link with online participants on the morning of the event day.
Venue: W1-C-909, Ito Campus, Kyushu University /
Event Official Language: English
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Seminar
Emergence of wormholes from quantum chaos
November 12 (Tue) at 16:30 - 18:00, 2024
Gabriele Di Ubaldo (Postdoctoral Researcher, iTHEMS)
I will give a broad introduction to some aspects of quantum gravity and the so-called black hole information problem. I will introduce wormholes as novel contributions to the gravitational path integral and how they provide a solution to the black hole information problem. Wormholes, however, are rather mysterious and we don’t have a good microscopic understanding of them and why we should include them in the our theory. In particular, wormholes seem to imply that gravity is not a proper quantum system but rather an average over a statistical ensemble of quantum systems. I will then transition into my own work which addresses these questions in the context of holography. I will show how wormholes in 3D quantum gravity can emerge from quantum chaos in the dual 2D Conformal Field Theory, without averaging. Wormholes capture coarse-grained properties of the CFT and conversely an individual chaotic CFT can effectively behave as an averaged system. Furthermore we will be able to explicitly factorize wormholes to extract microscopic information on black hole microstates. To achieve this I will (briefly) introduce and use tools such as Random Matrix Theory, the Gutzwiller Trace formula and Berry’s diagonal approximation, and the theory of SL(2,Z) non-holomorphic modular forms.
Venue: Hybrid Format (3F #359 and Zoom), Seminar Room #359
Event Official Language: English
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Seminar
Dynamics of Phase Transitions: Between First and Second Order
October 8 (Tue) at 16:00 - 17:30, 2024
Fumika Suzuki (CNLS Postdoctoral Research Associate, T4 / Center for Nonlinear Studies, Los Alamos National Laboratory, USA)
Phase transitions are typically classified as either first-order or second-order. The formation of topological defects in second-order phase transitions is well described by the Kibble-Zurek mechanism, while nucleation theory addresses first-order phase transitions. However, certain systems, such as superconductors and liquid crystals, can exhibit “weakly first-order” phase transitions that do not fit into these established frameworks. In this presentation, I introduce a new theoretical approach that combines the Kibble-Zurek mechanism with nucleation theory to explain topological defect formation in weakly first-order phase transitions. Additionally, I will discuss nonlinear quantum phase transitions that exhibit behaviors similar to weakly first-order transitions, which can be related to experiments with ultra-cold Rydberg atoms.
Venue: Hybrid Format (3F #359 and Zoom), Seminar Room #359 (Main Venue) / via Zoom
Event Official Language: English
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Seminar
Stringy Nonlocality: Operator Formalism and Implications
July 26 (Fri) at 14:00 - 15:30, 2024
Wei-Hsiang Shao (Ph.D. Student, Department of Physics, National Taiwan University, Taiwan)
Nonlocality is a fundamental property of string theory, where point-like particles are replaced by extended strings. This feature is especially evident in string field theories, where field components interact through form factors containing spacetime derivatives of infinite order. The usual approach to canonical quantization is no longer applicable, and thus a non-perturbative treatment of nonlocal effects at the quantum level remains unclear. In this seminar, I will discuss a recent attempt to construct an operator formalism for stringy nonlocal field theories, and explore the potential implications for black hole radiation and primordial fluctuations in the early universe.
Venue: Hybrid Format (3F #359 and Zoom), Seminar Room #359
Event Official Language: English
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Seminar
Quantum simulation of QCD matter: from hadronic scattering to gauge field qubit encoding
April 3 (Wed) at 10:00 - 11:00, 2024
Tianyin Li (Ph.D. Student, Institute of Quantum Matter, South China Normal University, China)
Recently, quantum computing (QC) has become a new method for solving non-perturbative problems in high-energy physics. Compared to traditional Monte Carlo simulations, the QC method does not encounter the sign problem, making it an effective approach for solving dynamical and finite density problems. The first part of this talk focuses on the quantum simulation of the hadronic scattering process, including the initial state parton distribution functions, intermediate state partonic scattering amplitudes, and final state hadronization. The second part of this talk concentrates on the qubit encoding of Hamiltonian formalism in lattice gauge field theory with a Coulomb gauge. As a preliminary attempt, the qubit encoding of (3+1)-dimensional Coulomb gauge QED will be discussed.
Venue: via Zoom
Event Official Language: English
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Seminar
Macroscopic neutrinoless double beta decay: long range quantum coherence
March 6 (Wed) at 15:30 - 17:30, 2024
Gordon Baym (Professor Emeritus, University of Illinois, USA)
This talk will introduce the concept of ``macroscopic neutrinoless double beta decay" (MDBD) for Majorana neutrinos. In this process an antineutrino produced by a nucleus undergoing beta decay, $X\to Y + e^- + \bar \nu_e$, is absorbed as a neutrino by another identical $X$ nucleus via the inverse beta decay reaction, $\nu_e + X \to e^-+Y$. The distinct signature of MDBD is that the total kinetic energy of the two electrons equals twice the end-point energy of single beta decay. The amplitude for MDBD, a coherent sum over the contribution of different mass states of the intermediate neutrinos, reflects quantum coherence over macroscopic distances, and is a new macroscopic quantum effect. We discuss the similarities and differences between the MDBD and conventional neutrinoless double beta decay, as well as give estimates of the rates of MDBD and backgrounds.
Venue: Hybrid Format (3F #359 and Zoom), Main Research Building (Main Venue) / via Zoom
Event Official Language: English
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Seminar
Dust-driven instabilities in protoplanetary disks: toward understanding formation of planetesimals
January 17 (Wed) at 10:30 - 11:30, 2024
Ryosuke Tominaga (Special Postdoctoral Researcher, Star and Planet Formation Laboratory, RIKEN Cluster for Pioneering Research (CPR))
Planet formation starts from collisional growth of sub-micron-sized dust grains in a gas disk called a protoplanetary disk. They are expected to grow toward km-sized objects called planetesimals. The resulting planetesimals further coalesce by gravity and form planets. However, there are some barriers preventing planetesimal formation, which includes fast radial drift and collisional fragmentation of dust grains. To circumvent the barriers and to explain planetesimal formation, previous studies have proposed hydrodynamic instabilities of dusty-gas disks. The instabilities can cause dust clumping, and planetesimals form if the resulting clumps collapse self-gravitationally. We have been investigating the linear/nonlinear development of these dust-gas instabilities. We also found a new instability driven by collisional growth of dust, which can bridge a potential gap between the first dust growth and the later planetesimal formation via the previous instabilities. In this talk, I will introduce our work on the dust-driven instabilities and their impact on planetesimal formation.
Venue: Hybrid Format (3F #359 and Zoom), Main Research Building
Event Official Language: English
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Seminar
Cosection localization via shifted symplectic geometry
December 6 (Wed) at 10:00 - 11:30, 2023
Young-Hoon 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 Li-Tian and Behrend-Fantechi. 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 1-form, the zero locus admits a (-2)-shifted symplectic structure and thus we have another virtual fundamental class by the Oh-Thomas construction. An obvious question is whether these two virtual fundamental classes coincide or not. In this talk, we will see that (-1)-shifted closed 1-forms 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
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Seminar
The Cosmic Gravitational Microwave Background
September 6 (Wed) at 15:00 - 16:30, 2023
Jan Schuette-Engel (Postdoctoral Researcher, iTHEMS)
The thermal plasma in the early universe produced a guaranteed stochastic gravitational wave (GW) background, which peaks today in the microwave regime and was dubbed the cosmic gravitational microwave background (CGMB). I show that the CGMB spectrum encodes fundamental information about particle physics and gravity at ultra high energies. In particular, one can determine from the CGMB spectrum the maximum temperature of the universe and the effective degrees of freedom at the maximum temperature. I also discuss briefly how quantum gravity effects arise in the CGMB spectrum as corrections to the leading order result.
Venue: Hybrid Format (3F #359 and Zoom), Main Research Building
Event Official Language: English
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Seminar
MNISQ: A Large-Scale Quantum Circuit Dataset for Machine Learning on/for Quantum Computers in the NISQ era
August 29 (Tue) at 14:00 - 15:30, 2023
Leonardo Placidi (Ph.D. Student, Graduate School of Engineering Science, Osaka University)
We introduce the first large-scale dataset, MNISQ, for both the Quantum and the Classical Machine Learning community during the Noisy Intermediate-Scale Quantum era. MNISQ consists of 4,950,000 data points organized in 9 subdatasets. Building our dataset from the quantum encoding of classical information (e.g., MNIST dataset), we deliver a dataset in a dual form: in quantum form, as circuits, and in classical form, as quantum circuit descriptions (quantum programming language, QASM). In fact, also Machine Learning research related to quantum computers undertakes a dual challenge: enhancing machine learning by exploiting the power of quantum computers, while also leveraging state-of-the-art classical machine learning methodologies to help the advancement of quantum computing. Therefore, we perform circuit classification on our dataset, tackling the task with both quantum and classical models. In the quantum endeavor, we test our circuit dataset with Quantum Kernel methods, and we show excellent results with up to 97% accuracy. In the classical world, the underlying quantum mechanical structures within the quantum circuit data are not trivial. Nevertheless, we test our dataset on three classical models: Structured State Space sequence model (S4), Transformer, and LSTM. In particular, the S4 model applied on the tokenized QASM sequences reaches an impressive 77% accuracy. These findings illustrate that quantum circuit-related datasets are likely to be quantum advantageous, but also that state-of-the-art machine learning methodologies can competently classify and recognize quantum circuits. We finally entrust the quantum and classical machine learning community.
Venue: #345, 3F, Main Research Building, RIKEN Wako Campus (Main Venue) / via Zoom
Event Official Language: English
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Seminar
Conserved charges in the quantum simulation of integrable spin chains
July 12 (Wed) at 13:30 - 15:00, 2023
Juan William Pedersen (Ph.D. Student, Graduate School of Arts and Sciences, The University of Tokyo)
In this talk, we present the result of the quantum simulation of the spin-1/2 Heisenberg XXX spin chain. We implement the integrable Trotterization algorithm, which allows us to control the Trotter error with conserved charges remaining conserved, on a real quantum computer and classical simulators. We study the effects of quantum noise on the time evolution of several conserved charges and specifically observe the decay of the expectation values. Our work improves our understanding of quantum noises and can potentially be applied to benchmark quantum devices and algorithms.
Venue: Seminar Room #359 (Main Venue) / via Zoom
Event Official Language: English
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Seminar
Gauge-equivariant neural networks as preconditioners in lattice QCD
April 6 (Thu) at 13:30 - 15:00, 2023
Tilo Wettig (Professor, Universität Regensburg, Germany)
We demonstrate that a state-of-the-art multi-grid preconditioner can be learned efficiently by gauge-equivariant neural networks. We show that the models require minimal re-training on different gauge configurations of the same gauge ensemble and to a large extent remain efficient under modest modifications of ensemble parameters. We also demonstrate that important paradigms such as communication avoidance are straightforward to implement in this framework.
Venue: Common Room #246-248 (Main Venue) / via Zoom
Event Official Language: English
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Seminar
Neutrinos from the big bang: probing cosmic gravitational inhomogeneities & magnetic fields in the early universe
March 13 (Mon) at 13:30 - 15:00, 2023
Gordon Baym (Professor Emeritus, University of Illinois, USA)
Primordial neutrinos from the Big Bang are about 100 times more prevalent than solar neutrinos, and at least two-thirds of them are now non-relativistic. These relic neutrinos, which have never been detected, decoupled in the early universe predominantly in helicity eigenstates. As I will discuss, their subsequent propagation through gravitational inhomogeneities and even background gravitational radiation, as well as cosmic and galactic magnetic fields partially flips their helicities, and can produce noticeable effects in their eventual detection. I will briefly mention future detection of relic neutrinos.
Venue: Common Room #246-248 (Main Venue) / via Zoom
Event Official Language: English
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Seminar
Algebra of symmetry in BF-like models in 3d and 4d
February 22 (Wed) at 14:00 - 15:30, 2023
Christophe Goeller (Humboldt Fellow, Ludwig-Maximilians-Universität München, Germany)
In this talk, I will discuss the construction of the boundary symmetry algebra for BF-like theories in 3D and 4D. In the 3D case, the theory corresponds to (an extension of) 3D gravity allowing for a source of curvature and torsion. I will show how the study of the current algebra and its associated Sugawara construction allows for two notions of quadratic charges (the usual diffeomorphism and its "dual") independently of boundary conditions. I will discuss their resulting algebra and its relation with the usual construction of the asymptotic boundary algebra. In the 4D case, a similar yet fundamentally different construction is possible, similarly resulting in multiple quadratic charges. I will discuss their constructions and their possible relations to 4D gravity.
Venue: Hybrid Format (Common Room 246-248 and Zoom)
Event Official Language: English
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Seminar
Searching for high-freqeuncy gravitational waves with axion detectors
January 12 (Thu) at 14:00 - 15:30, 2023
Valerie Domcke (Senior Faculty, Department of Theoretical Physics, CERN, Switzerland)
Current gravitational wave (GW) experiments cover a large frequency range from nHz to kHz. Beyond that, the regime of high frequency GWs is both extremely challenging challenging, and highly motivated as a unique window to the very early Universe. In this talk I will discuss a proposal for a new type of electromagnetic GW detector which makes use of the observation that GWs generate oscillating electromagnetic effects in the vicinity of external electric and magnetic fields. This is in close analogy to the interaction of the axion with electromagnetic fields. I will discuss how existing bounds from axion searches can be recast for GWs, as well as implications for future axion searches such as the DMRadio program.
Venue: Hybrid Format (Common Room 246-248 and Zoom)
Event Official Language: English
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Seminar
Lattice gauge theory in curved spacetimes
December 15 (Thu) at 14:00 - 15:30, 2022
Arata Yamamoto (Assistant Professor, Department of Physics, Graduate School of Science, The University of Tokyo)
Lattice gauge theory is a powerful computational approach in quantum field theory. It is also utilizable for investigating quantum phenomena in curved spacetimes, such as rotating frame, torsion, and gravitational backgrounds. In this talk, I would like to overview the formulation and results of lattice simulations in curved spacetimes.
Venue: Common Room #246-248 (Main Venue) / via Zoom
Event Official Language: English
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Seminar
Carrollian hydrodynamics near the black hole horizon
December 8 (Thu) at 16:00 - 17:30, 2022
Puttarak Jai-akson (Postdoctoral Researcher, iTHEMS)
The membrane paradigm provides a fascinating bridge between gravitational dynamics near black hole horizons (null boundaries) and fluid dynamics. One question naturally follows: what type of fluids and hydrodynamics emerged at the horizon? Contrary to the longstanding belief, it turns out that the horizon fluid is Carrollian, rather than the Galilean (Navier-Stokes) fluid. The Carroll geometries and Carrollian physics, arising originally when the speed of light goes to zero (c to 0 limit), have recently gained increasing attention in the fields of black hole physics and flat holography. In this presentation, I will talk about the Carrollian limit and the resulting Carroll geometries and this unusual kind of hydrodynamics, the Carrollian hydrodynamics. I will then present the geometrical construction of the membrane (also known as the stretched horizon) in a way that a Carroll geometry manifest, therefore allowing us to spell out precisely the dictionary between gravitational degrees of freedom on the membrane and the Carrollian fluid quantities. I will also show that the Einstein’s equations projected onto the horizon are the Carrollian hydrodynamic conservation laws. Lastly, I will discuss the covariant phase space of the horizon, symmetries, and conservation laws. The talk is based on arXiv:2209.03328 and arXiv:2211.06415.
Venue: Hybrid Format (Common Room 246-248 and Zoom)
Event Official Language: English
24 events