Abstract and Title to follow. Bio: Jonathan Braden is a Senior Research Associate at the Canadian Institute for Theoretical Astrophysics. His primary research interest is early Universe cosmology, with a particular focus on strong nonlinearity in the early Universe. Some specific topics include the dynamics of phase transitions, (p)reheating, and particle production during inflation; and the nonGaussian imprints of these phenomena in observational data. He is also interested in using analog early Universe experiments to build a "Universe on a table-top". He also has extensive experience in high performance computing, specifically the application of spectral and symplectic integration schemes to cosmology. He was previously a postdoctoral fellow at University College London. He received his PhD in Physics from the University of Toronto.

Abstract: When a binary merges to form a single black hole, the merger product emits a final burst of gravitational waves known as the “ringdown”. Ringdowns are currently being observed with LIGO and Virgo, and will be even stronger in future detectors like the Einstein Telescope or LISA. Observations of black hole ringdowns can be used to characterize binary merger remnants, and are particularly suited to test general relativity. So far, analyses of the ringdown have assumed linear black hole perturbation theory. In this talk, I will explore nonlinear effects during the ringdown, which could potentially spoil (or enhance) ringdown analysis. I will use numerical and analytic techniques to explore nonlinear effects both in a toy model (in anti-de Sitter), and then in asymptotically-flat black holes. I will conclude with some open problems in understanding the ringdown at nonlinear level, which could be an interesting avenue for analog experiments. Bio: Laura Sberna is currently a postdoc at the Max Planck Institute for Gravitational Physics, Potsdam, Germany. Besides the black hole ringdown, she is interested in the interplay between astrophysical environments and gravitational wave sources. Laura obtained her PhD at Perimeter Institute, Canada, under the supervision of Neil Turok.

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Abstract: Can we measure the ‘effective regularity’ of spacetime from the perturbation of quasi-normal mode (QNM) overtones? Black hole (BH) QNMs encode the resonant response of black holes under linear perturbations, their associated complex frequencies providing an invariant probe into the background spacetime geometry. In the late nineties, Nollert and Price found evidence of a BH QNM instability phenomenon, according to which perturbed QNMs of Schwarzschild spacetime migrate to new perturbed branches of different qualitative behaviour and asymptotics. Here we revisit this BH QNM instability issue by adopting a pseudospectrum approach. Specifically, we cast the QNM problem as an eigenvalue problem for a non-selfadjoint operator by adopting a hyperboloidal formulation of spacetime. Non-selfadjoint (more generally non-normal) operators suffer potentially of spectral instabilities, the notion of pseudospectrum providing a tool suitable for their study. We find evidence that perturbed Nollert & Price BH QNMs track the pseudospectrum contour lines, therefore probing the analytic structure of the resolvent, showing the following (in)stability behaviour: i) the slowest decaying (fundamental) mode is stable, whereas ii) (all) QNM overtones are ultraviolet unstable (for sufficiently high frequency). Building on recent work characterizing Burnett’s conjecture as a low-regularity problem in general relativity, we conjecture that (in the infinite-frequency limit) generic ultraviolet spacetime perturbations make BH QNMs migrate to ‘Regge QNM branches’ with a precise universal logarithmic pattern. This is a classical general relativity (effective) low-regularity phenomenon, agnostic to possible detailed (quantum) descriptions of gravity at higher-energies and potentially observationally accessible. Short bio: Jose Luis Jaramillo works at the Institut de Mathématiques de Bourgogne (IMB) in Dijon, in the Mathematical Physics group. He did his Ph.D at the Instituto de Astrofísica de Andalucía (IAA-CSIC), followed by postdoctoral stays at the Observatoire de Paris-Meudon, the Albert Einstein Institut (Max-Planck Institut for Gravitational Physics) in Golm and the Laboratoire de Physique Océanographique (LPO) in Brest (France). Since 2015 he is professor in the Mathematics Department at the Université de Bourgogne in Dijon.

Abstract: In the expanding universe, relativistic scalar fields are thought to be attenuated by “Hubble friction,” which results from the dilation of the underlying spacetime metric. By contrast, in a contracting universe this pseudofriction would lead to amplification. Here, we experimentally measure, with fivefold better accuracy, both Hubble attenuation and amplification in expanding and contracting toroidally shaped Bose-Einstein condensates, in which phonons are analogous to cosmological scalar fields. We find that the observed attenuation or amplification depends on the temporal phase of the phonon field, which is only possible for nonadiabatic dynamics. References: [1] Accurate Determination of Hubble Attenuation and Amplification in Expanding and Contracting Cold-Atom Universes; S. Banik, M. G. Galan, H. Sosa-Martinez, M. Anderson, S. Eckel, I. B. Spielman, and G. K. Campbell; Phys. Rev. Lett. 128 090401 (2022). doi:10.1103/PhysRevLett.128.090401 [2] A Rapidly Expanding Bose-Einstein Condensate: An Expanding Universe in the Lab; S. Eckel, A. Kumar, T. Jacobson, I. B. Spielman, and G. K. Campbell; Phys. Rev. X 8 21021 (2018). doi:10.1103/PhysRevX.8.021021 Ian Spielman is a fellow at the Joint Quantum Institute, National Institute of Standards and Technology and the University of Maryland.

Abstract: Since 2015, the LIGO-Virgo-KAGRA Collaboration has detected 90 signals from merging compact objects such as black holes and neutron stars. Each of these is analyzed using Bayesian inference, employing a stochastic algorithm such as Markov Chain Monte Carlo to compare data against models—thereby characterizing the source. However, this is becoming extremely costly as event rates grow with improved detector sensitivity. In this talk I will describe a powerful alternative using probabilistic deep learning to analyze each event in orders of magnitude less time while maintaining strict accuracy requirements. This uses simulated data to train a normalizing flow to model the posterior distribution over source parameters given the data—amortizing training costs over all future detections. I will also describe the use of importance sampling to establish complete confidence in these deep learning results. Finally I will describe prospects going forward for simulation-based inference to enable improved accuracy in the face of non-stationary or non-Gaussian noise. Bio: I am a Nottingham Research Fellow in gravitational waves at the School of Mathematical Sciences. My current interests are in black hole perturbation theory and machine-learning methods for data analysis. Prior to Nottingham, I spent five years at the Albert Einstein Institute in Potsdam, where I became a member of LIGO. I also did postdocs at the University of Guelph and Perimeter Institute, studying turbulence in gravitational waves and black hole instabilities. I obtained my PhD in physics at the University of Chicago under Robert Wald. My dissertation was on general relativistic backreaction effects in cosmology.

ABSTRACT: Extended atomic superfluids in the presence of a coherent coupling between two internal states represent a flexible platform to address open problems in condensed matter and fundamental physics. I will discuss their application to the experimental observation of a quantum phase transition from a para- to a ferromagnetic state. The nature of the transition is assessed by looking at the phase diagram as a function of the control parameters, at hysteresis phenomena, and at the magnetic susceptibility and the magnetization fluctuations around the critical point. Domain walls separating regions of opposite magnetization in the ferromagnetic state are created deterministically. I will also discuss the local decay of the metastable state into the real ground state leading to the probabilistic nucleation of bubbles. REFERENCE: Revealing the ferromagnetic phase transition in an extended two-component atomic superfluid; Riccardo Cominotti, Anna Berti, Clement Dulin, Chiara Rogora, Giacomo Lamporesi, Iacopo Carusotto, Alessio Recati, Alessandro Zenesini, Gabriele Ferrari; arXiv:2209.13235. SHORT BIO: Gabriele Ferrari is associate professor at the Physics Department of the University of Trento, Italy.

ABSTRACT Analogue physics is an interesting direction in modern Physics, based on the similarities of the mathematical models describing different systems. Such similarities were known for a very long time, the most famous example being the ubiquitous harmonic oscillator. However, the idea to use these similarities to study inaccessible systems and regimes in the lab has appeared relatively recently. The directions of research in analogue physics and associated effects include analogue gravity (Hawking emission1), early Universe (Kibble-Zurek mechanism2), high-energy physics (Klein tunnelling3, Zitterbewegung4), quantum simulations (Heisenberg model5), and others. In this talk, I will discuss a particularly interesting platform: a quantum fluid of strongly-coupled exciton-polaritons, often called a quantum fluid of light. Starting with an overall description of the state of the art on analogue black holes6, I will then turn to recent advances in polariton black hole simulations7. In particular, I will discuss the topological defects called quantum vortices, which can also be considered as charged relativistic particles8 obeying to the equations of analogue electrodynamics and gravity and allowing to simulate a Kerr black hole9 and to reproduce the Penrose effect. 1 W. G. Unruh, Phys. Rev. Lett. 46, 1351 (1981). 2 W. Zurek, Nature 317, 505 (1985). 3 M. I. Katsnelson et al, Nature Physics 2, 620 (2006). 4 J. Schliemann et al, Phys. Rev. Lett. 94, 206801 (2005). 5 C. Gross, I. Bloch, Science 357, 995 (2017). 6 C. Barcelo, Nat. Physics 15, 210 (2019). 7 M. J. Jacquet et al, Ph. Trans. Roy. Soc. A 378, 20190225 (2020). 8 D. Solnyshkov et al, Phys. Rev. B 85, 073105 (2012). 9 D. Solnyshkov et al, Phys. Rev. B 99, 214511 (2019) BIOSKETCH Dmitry Solnyshkov is a Professor of Physics (Solid State Physics) in University Clermont Auvergne (Clermont-Ferrand, France). Honorary member of the Institut Universitaire de France. Master of Physics obtained in St. Petersburg State Polytechnical University (Russia). PhD and second thesis (HDR) in University Blaise Pascal (France).Theoretician, author of more than 160 publications cited more than 6000 times, h=41 (WoS). Contributed to 4 books. Co-supervised 9 PhD students. Research topics in fundamental and applied physics: Bose-Einstein condensation, strong light-matter coupling, quantum fluids, topological physics, lasers and optical devices, 2D materials, analogue physics.

Abstract: "In this seminar I will discuss methods for extracting, testing, and designing effective field theory descriptions for continuous (quantum) field theory simulators. After introducing general concepts for the preparation, design, and detection of effective field theories in cold atom systems, I will present our latest results on the floquet engineered sine-Gordon model, emerging as the effective quantum field theory description of two tunnel-coupled quantum wires, and on parametrically driven classical two-fluid interfaces as analogue simulators for the onset of nonlinearities in preheating dynamics. Special focus will be on factorization properties of higher-order correlations as sensitive probes for nonlinear dynamics in strongly correlated field theories which opens a window in the experimental extraction of emergent field theory descriptions for complex many-body systems." Biosketch: Sebastian Erne is a Senior Research Associate at the Atominstitut of the Vienna Technical University. His primary research is focused on non-equilibrium quantum many-body systems in the interface between experiment and theory. His main research interests are analogue cold-atom simulators for precision experiments of quantum field theory with applications to early Universe cosmology, quantum field theory in curved spacetime, the Unruh effect, equal time formulations of QFT, universal physics close to and far from equilibrium, and high performance computing for the modeling of complex quantum systems.

"In this seminar I will introduce the capabilities of ultracold gases to address fundamental questions in quantum field theory. I will introduce the experimental capabilities in preparation and detection of quantum fields in atomic gases. A special focus will be on our latest result on the implementation of curved spacetime for a scalar massless quantum field. We have shown that positive as well as negative curvature can be experimentally realized and can be dialed in as needed. We also used the experiment/simulator to reveal particle production in an accelerating, decelerating and constantly expanding spacetime. Employing Sakharov oscillations for detecting the production of excitations opens a window to add to the power spectrum also phase information about the excitations." Markus Oberthaler is a professor, chair of experimental physics at Kirchhoff-Institute for Physics,Heidelberg University. His main research fields are Quantum Entanglement in many particle systems and quantum simulation, precision experiment testing quantum field theory, quantum metrology, immersed quantum systems, universal physics far from equilibrium and connection to high energy physics, environmental physics and dating of water and ice with Argon Trap Trace Analysis (ATTA).

ABSTRACT False vacuum decay plays an important role in many cosmological scenarios, while also acting as an important keystone model for nonequilibrium quantum field theory. It was recently realized that dilute gas Bose-Einstein condensates (BECs) can be used to emulate the dynamics of relativistic vacuum decay, providing a unique experimental window into the early Universe. Making optimal use of these experiments requires a detailed understanding of the theoretical predictions for vacuum decay. I will discuss some recent work on the role of short-wavelength fluctuations in real-time simulations of false vacuum decay, focussing on the case of pure scalar field theory. This includes renormalization effects, which capture averaged effects of fluctuations on the long-wavelength dynamics, as well as stochastic contributions where the long-wavelength modes are sensitive to the particular realization of the short-wavelengths. I will comment on the implications of these results for BEC experiments. Finally, time (and audience interest) permitting, I will discuss how the evolution of a dilute gas BEC system can be mapped onto another important nonlinear epoch in the early Universe --- the end-of-inflation. BIO Jonathan Braden is a Senior Research Associate at the Canadian Institute for Theoretical Astrophysics. His primary research interest is early Universe cosmology, with a particular focus on strong nonlinearity in the early Universe. Some specific topics include the dynamics of phase transitions, (p)reheating, and particle production during inflation; and the nonGaussian imprints of these phenomena in observational data. He is also interested in using analog early Universe experiments to build a "Universe on a table-top". He also has extensive experience in high performance computing, specifically the application of spectral and symplectic integration schemes to cosmology. He was previously a postdoctoral fellow at University College London. He received his PhD in Physics from the University of Toronto.

ABSTRACT: Phase transitions and critical phenomena have been at the heart of many-body physics, and quantum simulations with cold atoms from the beginning. While almost all phase transitions in cold atoms systems are continuous, there is a renewed interest also in discontinuous (first-order) phase transitions and the quantum metastability, whose relativistic analogues are believed to play an important role in early-universe cosmology (false vacuum decay). We experimentally demonstrate a novel level of control over a quantum phase transition by combining an optical lattice with an uncommon type of Floquet engineering based on a resonant drive. Contrary to most applications of periodic driving, where the drive frequency is selected to avoid all resonances, we resonantly couple the lowest two bands of a lattice. With this drive, we can not only induce the superfluid to Mott insulator transition but are furthermore able to control its character and turn the Mott transition from a continuous into a discontinuous transition, thereby opening the door to quantum simulations of the early universe and interacting topological transitions in condensed matter systems. BIO: Prof. Ulrich Schneider is a Professor of Many-Body Physics at the University of Cambridge. His work is centred on employing ultracold atoms in optical lattices as a testbed to study Quantum Many-Body Dynamics. His scientific interests range from quantum thermodynamics, low-dimensional systems, and strongly correlated systems to topological effects and many-body localization. Prof. Schneider studied physics in Kaiserslautern and Sheffield, received his PhD from the Johannes-Gutenberg University Mainz, and worked as a senior scientist at the Ludwig-Maximilians-University (LMU) and the Max-Planck-Institute for Quantum Optics (MPQ) in Munich. He is a fellow of Jesus College, received the 2015 Rudolf-Kaiser Prize, and the recipient of ERC Starting (2016, Quasicrystal) and Consolidator (2021, Kagome) grants. In 2020 he also joined the AION collaboration building an Atom Interferometer and Observatory Network. The seminar will last 1 hour including Q&A and be held at 3.00pm UK Time/10.00am Toronto Time. This seminar will be held on Zoom.

Abstract: After some background on first order transitions in the early universe I’ll describe a new physical system that might be used as a laboratory analogue. The system is based on a spin 1 Bose gas with Raman and RF induced interactions. It does not require the Feshbach resonance and modulated interactions of previous proposals. Based on work by Ian Moss, Tom Billam and Kate Brown. Biosketch: Ian Moss is Professor of Theoretical Cosmology at Newcastle University. He has been been researching early universe phase transitions for what seems like forever and he is half of the Hawking-Moss instanton. The seminar will last 1 hour including Q&A and be held at 3.00pm UK Time/10.00am Toronto Time. This seminar will be held on Zoom.

Maxime Jacquet (Laboratoire Kastler Brossel,Quantum Optics Group, Paris, France), on "Quantum vacuum excitation of a quasi-normal mode in an analog model of black hole spacetime" Biosketch: Maxime is currently leading experimental and theoretical research in analogue gravity with quantum fluids of light in the Quantum Optics group at Laboratory Kastler Brossel, Sorbonne University and CNRS, France. Abstract: Analogue gravity enables the laboratory investigation of effects of quantum field theories on curved spacetimes. The archetypal example is the parametric amplification of vacuum quantum fluctuations of the field on the curved spacetime, as in the Hawking effect (the correlated emission of waves) at the event horizon. In this talk, I will review theoretical work on the Hawking effect in transsonic, quantum fluids of microcavity polaritons [1]. Because of the driven-dissipative dynamics of the fluid, the system is out of thermal equilibrium. I will explain how this impacts correlated emission by the Hawking effect [2], and also show that dissipation may be harnessed to observe novel effects like the quantum vacuum excitation of quasi-normal modes of the acoustic field [3]. This, I will argue, opens a range of new questions pertaining to all quantum fields on black hole spacetimes beyond analogue models. Refs: [1] arxiv:2002.00043, [2] arxiv:2201.02038, [3] arxiv:2110.14452. The seminar will last 1 hour including Q&A and be held at 3.00pm UK Time/10.00am Toronto Time. This seminar will be held on Zoom.

Abstract: False vacuum decay in quantum mechanical first order phase transitions is a phenomenon with wide implications in cosmology and presents interesting theoretical challenges. In the standard approach, it is assumed that false vacuum decay proceeds through the formation of bubbles that nucleate at random positions in spacetime and subsequently expand. In our work, we investigated the presence of correlations between bubble nucleation sites using a recently proposed semiclassical stochastic description of vacuum decay. The procedure sampled vacuum fluctuations which were evolved using classical lattice simulations. We computed the two-point function for bubble nucleation sites from an ensemble of simulations, demonstrating that nucleation sites cluster in a way that is qualitatively similar to peaks in random Gaussian fields. I will comment qualitatively on the phenomenological implications of bubble clustering in early Universe phase transitions, which include features in the power spectrum of stochastic gravitational waves and an enhancement or suppression of the probability of observing bubble collisions in the eternal inflation scenario. I finish by explaining briefly how our results can be tested empirically using a table-top analogue of vacuum decay. Biosketch: Dalila Pirvu is a second year PhD student at the Perimeter Institute and University of Waterloo in Canada. She did her undergraduate at Imperial College London. Her work is focused on dynamical lattice simulations of phase transitions in quantum field theories. The seminar will last 1 hour including Q&A and be held at 3.00pm UK Time/10.00am Toronto Time. This seminar will be held on Zoom. Details to follow

Abstract: I will outline the diverse theoretical arguments for why quantum mechanics of merging black holes should lead to the stimulation of Hawking Radiation of gravitational waves, which may manifest as delayed echoes in observations. I will then summarize the status and outlook of the observational program to search for these echoes. Biosketch: Niayesh Afshordi is an Astrophysicist whose research spans from Early Universe Cosmology and Quantum Gravity, to Dark Matter, Dark Energy, Extragalactic Astronomy, Large Scale Structure of the Universe, and High Energy Astrophysics. He received his PhD at Princeton in 2004. He then did postdocs at Harvard College Observatory and Perimeter Institute for Theoretical Physics. He is currently a professor of Physics and Astronomy at the University of Waterloo. He is also an associate faculty at Perimeter Institute, and a founding faculty of the Waterloo Centre for Astrophysics. The seminar will last 1 hour including Q&A and be held at 3.00pm UK Time/10.00am Toronto Time. This seminar will be held on Zoom.

Superradiance is the amplification ofwaves scattered by a rapidly rotating object, first proposed by Roger Penroseas a way to extract energy from rotating black holes. Despite being afundamental process in wave physics, astrophysical superradiance has not beenobserved yet due to the large distances involved. However, proposal based onanalogue gravity studies have demonstrated their versatility providing the firstmeasurement of superradiance in a hydrodynamic experiment. Here we report the first measurementof Penrose superradiance in nonlinear optical systems, especially in a 2Dsuperfluid. A weak signal beam with orbital angular momentum is focused ontothe core of a pump vortex. In the scattering, a negative norm idler wave isgenerated and trapped inside the pump core, while the signal (positive normwave) gets amplified. Our results demonstrate the presence of Penrosesuperradiance in superfluids unveiling the key role of the negative norm modein the amplification process. Maria Chiara Braidotti is a research associateat the School of Physics & Astronomy of the University of Glasgow (UoG),Scotland. She joined works in the ExtremeLight group lead by Prof. Faccio, UoG(http://www.physics.gla.ac.uk/XtremeLight/index.html). Her main expertise is theoretical andexperimental nonlinear optics, especially using it as a tool to testfundamental processes at the interface between gravitation and quantummechanics. In recent years, her research activity has focused on the test ofPenrose process and Zel’dovich effect both involving amplification ofelectromagnetic modes from the scattering with a rotating body. She is author of more than 15 publications ininternational journals (with 2 publications on Physics Review Letters journal)and over 30 invited presentations to national and international conferences.