Format results
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Magnetic Quivers and Phase Diagrams in 6 dimensions
Amihay Hanany Imperial College London
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Open Quantum Dynamics with Nonlinearly Realized Symmetries.
Jury Radkovski Perimeter Institute for Theoretical Physics
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Late-time signals from binary black hole mergers
Marina de Amicis -
The Gaudin model in the Deligne category Rep $GL_t$
Leonid Rybnikov -
Adventures in Flat Holography
Sabrina Pasterski Perimeter Institute for Theoretical Physics
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Looking for Low-Frequency Dark Matter in the Lab
Saarik KaliaDark photons and axions are exciting candidates for dark matter, which may be observable through their couplings to electromagnetism or electrons. While many experimental programs have been developed to explore the wide range of parameter space over which these candidates may exist, the mass range corresponding to frequencies below a kHz has been seldom probed by laboratory experiments. In this talk, I will discuss two ongoing efforts to probe this region of parameter space. Both rely on the ability of dark-photon or axion dark matter to source an oscillating magnetic field signal inside an experimental apparatus. In the first case, this magnetic field signal is detected by observing its effect on magnetically levitated (Maglev) systems. The oscillating magnetic field signal sourced by dark matter can drive translational motion of a levitated superconductor or rotational motion of a levitated ferromagnet. As mechanical resonators, Maglev systems are naturally sensitive to lower frequencies, making them well-suited detectors for sub-kHz dark matter candidates. In the second case, we instead consider Earth as the experimental apparatus. That is, we search directly for the oscillating magnetic field signal using unshielded magnetometers located across the Earth's surface. Not only does the signal strength receive an enhancement from the large size of the Earth, but it is also correlated between independent measurements at different locations. I will discuss the search for this signal in existing publicly available magnetometer data maintained by the SuperMAG collaboration, as well as an independent experimental effort, known as SNIPE Hunt, to measure this signal in the field. I will show that both Maglev systems and unshielded magnetometers have the potential to set the leading laboratory constraints on dark-photon and axion dark matter in the sub-kHz regime.
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Phase Spaces and Operator Algebras for Subregions in Gauge Theory and Quantum Gravity
Marc Klinger University of Illinois
What does it mean to specify a subregion in a diffeomorphism invariant fashion? This subtle question lies at the heart of many deep problems in quantum gravity. In this talk, we will explore a program of research aimed at answering this question. The two principal characters of the presentation are the extended phase space and the crossed product algebra. The former furnishes a symplectic structure which properly accounts for all of the degrees of freedom necessary to invariantly specify a subregion in gauge theory and gravity, while the latter serves as a quantization of this space into an operator algebra which formalizes the observables of the associated quantum theory. The extended phase space and the crossed product were originally motivated by the problems of the non-invariance/non-integrability of symmetry actions in naive subregion phase spaces, and the non-factorizability/divergence of entanglement entropy in naive subregion operator algebras. The introduction of these structures resolves these issues, while the correspondence between them unifies these resolutions. To illustrate the power of our framework, we demonstrate how the modular crossed product of semiclassical quantum gravity can be reproduced via this approach. We then provide some remarks on how this construction may be augmented in the non-perturbative regime, leading to the notion of a `fuzzy subregion'. We conclude with remarks on currently ongoing and future work, which includes applications to asymptotic and corner symmetries, quantum reference frames, generalized entropy, and the definition of quantum diamonds.
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Revealing the information content of galaxy n-point functions with simulation-based inference
Beatriz TucciImproving cosmological constraints from galaxy clustering presents several challenges, particularly in extracting information beyond the power spectrum due to the complexities involved in higher-order n-point function analysis. In this talk, I will introduce novel inference techniques that allow us to go beyond the state-of-the-art, not only by utilizing the galaxy trispectrum, a task that remains computationally infeasible with traditional methods, but also by accessing the full information encoded in the galaxy density field for the first time in cosmological analysis. I will present simulation-based inference (SBI), a powerful deep learning technique that enables cosmological inference directly from summary statistics in simulations, bypassing the need for explicit analytical likelihoods or covariance matrices. This is achieved using LEFTfield, a Lagrangian forward model based on the Effective Field Theory of Large Scale Structure (EFTofLSS) and the bias expansion, ensuring robustness on large scales. Furthermore, LEFTfield enables field-level Bayesian inference (FBI), where a field-level likelihood is used to directly analyze the full galaxy density field rather than relying on compressed statistics. I will conclude by exploring the question of how much cosmological information can be extracted at the field level through a comparison of σ8 constraints obtained from FBI, which directly uses the 3D galaxy density field, and those obtained from n-point functions via SBI.
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Magnetic Quivers and Phase Diagrams in 6 dimensions
Amihay Hanany Imperial College London
Higgs branches in theories with 8 supercharges change as one tunes the gauge coupling to critical values. This talk will focus on six dimensional (0,1) supersymmetric theories in studying the different phenomena associated with such a change. Based on a Type IIA brane system, involving NS5 branes, D6 branes and D8 branes, one can derive a "magnetic quiver” which enables the construction of the Higgs branch using a “magnetic construction” or as a more commonly known object “3d N=4 Coulomb branch”. Interestingly enough, the magnetic construction opens a window to a new set of Higgs branches which were not available using the well studied method of hyperkähler quotient. It turns out that exceptional global symmetries are fairly common in the magnetic construction, and few examples will be shown. In all such cases there are strongly coupled theories where Lagrangian description fails, and the magnetic construction is helpful in finding properties of the theory. Each Higgs branch can be characterized by a phase diagram which describes the different sets of massless fields around vacua. We will use such diagrams to study how Higgs branches change. If time permits we will show an interesting exceptional sequence consisting of SU(3) — G2 — SO(7).
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Pairwise Difference Learning
Karim BelaidPairwise difference learning (PDL) has recently been introduced as a new meta-learning technique for regression by Wetzel et al. Instead of learning a mapping from instances to outcomes in the standard way, the key idea is to learn a function that takes two instances as input and predicts the difference between the respective outcomes. Given a function of this kind, predictions for a query instance are derived from every training example and then averaged. This presentation focus on the classification version of PDL, proposing a meta-learning technique for inducing a classifier by solving a suitably defined (binary) classification problem on a paired version of the original training data. This presentation will also discuss an enhancement to PDL through anchor weighting, which adjusts the influence of anchor points based on the reliability and precision of their predictions, thus improving the robustness and accuracy of the method. We analyze the performance of the PDL classifier in a large-scale empirical study, finding that it outperforms state-of-the-art methods in terms of prediction performance. Finally, we provide an easy-to-use and publicly available implementation of PDL in a Python package.
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Open Quantum Dynamics with Nonlinearly Realized Symmetries.
Jury Radkovski Perimeter Institute for Theoretical Physics
In the framework of Non-Equilibrium Field Theory, I will construct the effective influence functional — generator of non-equilibrium correlation functions — for a mechanical system with degrees of freedom living on a group (e.g. rigid body) interacting with a thermal bath at high temperature. I will derive the constraints on the influence functional following from the group symmetry structure and the DKMS symmetry — generalization of the fluctuation-dissipation theorem. At the linear response level, group symmetry turns out to impose more constraints compared to DKMS. I will illustrate the general formalism with the diffusion in a Fermi gas and exhibit the large-N suppression of the non-linear response. Finally, I will introduce the Universal Bath — the generalization of the Caldeira-Leggett model. It is a dual field theory defined in one extra dimension that reproduces the classical non-equilibrium dynamics of the mechanical system. I will show that in the limit of Ohmic dissipation, when the temperature becomes the only relevant scale at play, the Universal Bath also reproduces the quantum corrections.
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Doob's Lagrangian: A Sample-Efficient Variational Approach to Transition Path Sampling
Kirill NeklyudovThe 3rd talk of a monthly webinar series jointly hosted by Perimeter, IVADO, and Institut Courtois. Rare event sampling in dynamical systems is a fundamental problem arising in the natural sciences, which poses significant computational challenges due to an exponentially large space of trajectories. For settings where the dynamical system of interest follows a Brownian motion with known drift, the question of conditioning the process to reach a given endpoint or desired rare event is definitively answered by Doob's h-transform. However, the naive estimation of this transform is infeasible, as it requires simulating sufficiently many forward trajectories to estimate rare event probabilities. In this talk, I'll present our recent findings on the variational formulation of Doob's h-transform as an optimization problem over trajectories between a given initial point and the desired ending point. To solve this optimization, we propose a simulation-free training objective with a model parameterization that imposes the desired boundary conditions by design. Our approach significantly reduces the search space over trajectories and avoids expensive trajectory simulation and inefficient importance sampling estimators which are required in existing methods. We demonstrate the ability of our method to find feasible transition paths on real-world molecular simulation and protein folding tasks.
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Towards realistic tensor network holography using loop gravity
Simon LangenscheidtPIRSA:24110084In order to understand many Quantum information aspects of the Ads/CFT correspondence, tensor network toy models of holography have been a useful and concrete tool. However, these models traditionally lack many features of their continuum counterparts, limiting their applicability in arguments about gravity. In this talk, I present a natural extension of the tensor network holography paradigm which rectifies some of these issues. Its direct inspiration originates in Loop Quantum Gravity, which allows not only lifting existing limitations of tensor networks, but also firmly grounds the models in the context of nonperturbative canonical quantum gravity.
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Late-time signals from binary black hole mergers
Marina de AmicisLate-time tails emitted by binary black holes mergers contain invaluable information on the spacetime’s asymptotic structure. Perturbative numerical simulations of extreme mass-ratio mergers have revealed that these tails are enhanced by several orders of magnitude with the progenitors’ binary eccentricity. This amplification has the potential to bring tails within the realm of observation and shows that this effect carries significant astrophysical implications, other than fundamental physics content. I will present an analytical perturbative model that accurately predicts the numerically observed tail and explains its enhancement with the progenitors' binary eccentricity. The model is an integral over the system's entire history, showing how the post-ringdown tail is inherited from the non-circular inspiral in a non-local fashion. I will prove the tail to be a superposition of many power-laws, with each term's excitation coefficient depending on the specific inspiral history. A single power law is recovered only in the limit of asymptotically late times, consistent with Price's results and the classical soft-graviton theorem. Finally, I will introduce a robust framework for extracting tails in fully non-linear simulations of equal masses mergers. I will present results for late-time tails emitted by these systems and discuss their phenomenology. -
The Gaudin model in the Deligne category Rep $GL_t$
Leonid RybnikovDeligne's category $D_t$ is a formal way to define the category of finite-dimensional representations of the group $GL_n$ with $n=t$ being a formal parameter (which can be specialized to any complex number). I will show how to interpolate the construction of the higher Hamiltonians of the Gaudin quantum spin chain associated with the Lie algebra $\mathfrak{gl}_n$ to any complex $n$, using $D_t$. Next, according to Feigin and Frenkel, Bethe ansatz equations in the Gaudin model are equivalent to no-monodromy conditions on a certain space of differential operators of order $n$ on the projective line. We also obtain interpolations of these no-monodromy conditions to any complex $n$ and prove that they generate the relations in the algebra of higher Gaudin Hamiltonians for generic complex $n$. I will also explain how it is related to the Bethe ansatz for the Gaudin model associated with the Lie superalgebra $\mathfrak{gl}_{m|n}$. This is joint work with Boris Feigin and Filipp Uvarov, https://arxiv.org/abs/2304.04501. -
Adventures in Flat Holography
Sabrina Pasterski Perimeter Institute for Theoretical Physics
Celestial Holography encompasses a decade-long endeavor to understand a flat space realization of the holographic principle starting from symmetries in the infrared. But where does it fit within other attempts at constructing a flat hologram? This colloquium delves into some fun tensions in the literature and hopes for resolving them.
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Brownian Circuits and Quantum Randomness
Gregory BentsenAbstract: Randomness is a powerful resource for information-processing applications. For example, classical randomness is essential for modern information security and underpins many cryptographic schemes. Similarly, quantum randomness can protect quantum information against noise or eavesdroppers who wish to access or manipulate that information. These observations raise a set of related questions: How quickly and efficiently can we generate quantum randomness? How much quantum randomness is necessary for a given task? What can we use quantum randomness for? In this talk, I address these questions using all-to-all Brownian circuits, a family of random quantum circuits for which exact results can often be obtained via mean-field theory. I will first demonstrate that all-to-all Brownian circuits form k-designs in a time that scales linearly with k. I will then discuss how these circuits can be applied to study Heisenberg-limited metrology and quantum advantage. In particular, I will discuss a time-reversal protocol that can achieve Heisenberg-limited precision in cavity QED and trapped ion setups; I will also discuss the application of these circuits to studying classical spoofing algorithms for the linear cross-entropy benchmark, a popular measure of quantum advantage.