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Social Learning and Sample Herding in Networks with Homophily
Matt Jackson (Stanford)Quantum Impulse Sensing with Mechanical Sensors in the Search for Dark Matter
Sohitri Ghosh University of Maryland, College Park
Holographic measurement and bulk teleportation
Stefano Antonini University of Maryland, College Park
Hidden symmetries in cosmology and black holes
Francesco Sartini Okinawa Institute of Science and Technology Graduate University
Emergent time and reconstruction of the black hole interior
Lampros Lamprou Massachusetts Institute of Technology (MIT) - Department of Physics
Too Much Data: Externalities and Inefficiencies in Data Markets
Azarakhsh Malekian (U. Toronto)Measurement-induced phase transitions on dynamical quantum trees
Xiaozhou Feng Ohio State University
Experimental and Observational Studies in the Presence of Stochastic Networks
Alex Volfovsky (Duke)The back-reaction problem in quantum foundations and gravity
Jonathan Oppenheim University College London
Organizing Modular Production
Bryony Reich (Northwestern)We characterize the optimal communication network in a firm with a modular production function, which we model as a network of decisions with a non-overlapping community structure. Optimal communication is characterized by two hierarchies that determine whom each agent receives information from and sends information to. Receiver rank depends only on module cohesion while sender rank also depends on decision-specific values of adaptation. When the hierarchies are the reverse of each other, optimal communication is bottom up in aggregate, and when they are the same, it has a core-periphery structure, in which the core contains the most cohesive modules.Social Learning and Sample Herding in Networks with Homophily
Matt Jackson (Stanford)Other peoples' experiences serve as primary sources of information about the potential payoffs to various available opportunities. Homophily in social networks affects both the quality and diversity of information to which people have access.On the one hand, homophily provides higher quality information since observing the experiences of another person is more informative as that person is more similar to the decision maker. On the other hand, homophily lowers the variety of actions about which people can learn when a group ends up herding on specific actions about which they have better information. This can lead to inefficiencies and inequalities across groups, as we show. Homophily lowers efficiency and increases inequality in sparse networks, while enhancing efficiency and decreasing inequality in denser networks. We characterize conditions under which groups herd on separate actions, and show how such homophily-induced herding driven by limited scope of information differs from standard forms of herding driven by cascading inferences.Quantum Impulse Sensing with Mechanical Sensors in the Search for Dark Matter
Sohitri Ghosh University of Maryland, College Park
Recent advances in mechanical sensing technologies have led to the suggestion that heavy dark matter candidates around the Planck mass range could be detected through their gravitational interaction alone. The Windchime collaboration is developing the necessary techniques, systems, and experimental apparatus using arrays of optomechanical sensors that operate in the regime of high-bandwidth force detection, i.e., impulse metrology. Today's sensors can be limited by the added noise due to the act of measurement itself. Techniques to go beyond this limit include squeezing of the light used for measurement and backaction evading measurement by estimating quantum non-demolition operators — typically the momentum of a mechanical resonator well above its resonance frequency. In this talk, we will discuss the theoretical limits to noise reduction using such quantum enhanced readout techniques for these optomechanical sensors.
Holographic measurement and bulk teleportation
Stefano Antonini University of Maryland, College Park
In holography, spacetime is emergent and its properties depend on the entanglement structure of the dual theory. An interesting question is how changes in the entanglement structure affect the bulk dual description. In this talk, I will describe how local projective measurements performed on a subregion of the boundary theory modify the bulk dual spacetime. The post-measurement bulk is cut off by end-of-the-world branes and is dual to the complementary unmeasured region . Using a bulk calculation in —which involves a phase transition triggered by the measurement—and tensor network models of holography, I will show that the portion of bulk preserved after the measurement depends on the size of and the state we project on. Interestingly, the post-measurement bulk includes regions that were part of the entanglement wedge of before the measurement. Our results indicate that the effect of a measurement performed on a subregion of the boundary is to teleport part of the bulk information contained in into the complementary region . Finally, I will comment on applications to the eternal black hole in JT gravity (dual to the SYK thermofield double state) and the relationship between measurements and traversable wormholes.
Hidden symmetries in cosmology and black holes
Francesco Sartini Okinawa Institute of Science and Technology Graduate University
Cosmological models and black holes belong to classes of space-time metrics defined in terms of a finite number of degrees of freedom, for which the Einstein–Hilbert action reduces to a one-dimensional mechanical model. We investigate their classical symmetries and the algebra of the corresponding Noether charges. These dynamical symmetries have a geometric interpretation, not in terms of spacetime geometry, but in terms of motion on the field space. Moreover, they interplay with the fiducial scales, introduced to regulate the homogenous model, suggesting a relationship with the boundary symmetries of the full theory.
Finally, the existence of these symmetries unravels new aspects of the physics of black holes and cosmology. It opens the way towards a rigorous group quantization of the reduced model and to the study of their holographic properties. It might have significant consequences on the propagation of test fields and the corresponding perturbation theory.
Zoom link: https://pitp.zoom.us/j/92846533238?pwd=cERGUjd6OXB5S0ZaSzVIdVJyMHZxUT09
Experimentation on Networks
Moritz Meyer-ter-Vehn (UCLA)We introduce a model of strategic experimentation on social networks where forward-looking agents learn from their own and neighbors’ successes. In equilibrium, private discovery is followed by social diffusion. Social learning crowds out own experimentation, so total information decreases with network density; we determine density thresholds below which agents asymptotically learn the state. In contrast, agent welfare is single-peaked in network density, and achieves a second-best benchmark level at intermediate levels that achieve a balance between discovery and diffusion. We also study how learning and welfare differ across directed, undirected and clustered networks.Emergent time and reconstruction of the black hole interior
Lampros Lamprou Massachusetts Institute of Technology (MIT) - Department of Physics
I will present a general bulk reconstruction technique in AdS/CFT suitable for addressing a facet of the black hole information problem: How to unambiguously predict the results of measurements performed by an infalling observer in the black hole interior.
I will explicitly apply the method in the AdS_2/SYK correspondence. My proposal provides an internal notion of time for quantum gravitational systems that may be useful for cosmology.Surrogate model for gravitational wave signals from black hole binaries built on black hole perturbation theory waveforms calibrated to numerical relativity : one model to rule both comparable and extreme mass ratio regime
Tousif Islam University of Massachusetts Dartmouth
We present a reduced-order surrogate model of gravitational waveforms from non-spinning binary black hole systems with comparable to large mass-ratio configurations. This surrogate model, BHPTNRSur1dq1e4, is trained on waveform data generated by point-particle black hole perturbation theory (ppBHPT) with mass ratios varying from 2.5 to 10,000. BHPTNRSur1dq1e4 can generate waveforms up to 30,500 m1(where m1 is the mass of the primary black hole), includes several more spherical harmonic modes up to \ell=10, and calibrates both dominant and subdominant modes to numerical relativity (NR) data. In the comparable mass-ratio regime, including mass ratios as low as 2.5, the gravitational waveforms generated through ppBHPT agree surprisingly well with those from NR after this simple calibration step. We argue that this scaling essentially captures higher order self-force corrections in a much simpler way. We also compare our model to recent SXS and RIT NR simulations at mass ratios ranging from 15 to 32, and find the dominant quadrupolar modes agree to better than≈10−3. We expect our model to be useful to study intermediate-mass-ratio binary systems in current and future gravitational-wave detectors. Finally, we discuss avenues for improving the model by extending its region of validity.
Zoom link: https://pitp.zoom.us/j/99971588372?pwd=ZVUveUlNeTI1SE5iMzNnVDh0L2xkQT09
Too Much Data: Externalities and Inefficiencies in Data Markets
Azarakhsh Malekian (U. Toronto)When a user shares her data with online platforms, she reveals information about others in her social network. In such a setting, network externalities depress the price of data because once a user's information is leaked by others, she has less reason to protect her data and privacy. These depressed prices lead to excessive data sharing. We characterize conditions under which shutting down data markets improves welfare. Platform competition does not redress the problem of excessively low data prices and too much data sharing and may further reduce welfare. We propose a scheme based on mediated data sharing that improves efficiency.Measurement-induced phase transitions on dynamical quantum trees
Xiaozhou Feng Ohio State University
Monitored many-body systems fall broadly into two dynamical phases, ``entangling'' or ``disentangling'', separated by a transition as a function of the rate at which measurements are made on the system. Producing an analytical theory of this measurement-induced transition is an outstanding challenge. Recent work made progress in the context of tree tensor networks, which can be related to all-to-all quantum circuit dynamics with forced (postselected) measurement outcomes. So far, however, there are no exact solutions for dynamics of spin-1/2 degrees of freedom (qubits) with ``real'' measurements, whose outcome probabilities are sampled according to the Born rule. Here we define dynamical processes for qubits, with real measurements, that have a tree-like spacetime interaction graph, either collapsing or expanding the system as a function of time. The former case yields an exactly solvable measurement transition. We explore these processes analytically and numerically, exploiting the recursive structure of the tree. We compare the case of ``real'' measurements with the case of ``forced'' measurements. Both cases show a transition at a nontrivial value of the measurement strength, with the real measurement case exhibiting a smaller entangling phase. Both exhibit exponential scaling of the entanglement near the transition, but they differ in the value of a critical exponent. An intriguing difference between the two cases is that the real measurement case lies at the boundary between two distinct types of critical scaling. On the basis of our results we propose a protocol for realizing a measurement phase transition experimentally via an expansion process.
Experimental and Observational Studies in the Presence of Stochastic Networks
Alex Volfovsky (Duke)Dynamic network data have become ubiquitous in social network analysis, with new information becoming available that captures when friendships form, when corporate transactions happen and when countries interact with each other. Moreover, data are available about individual actors in the network, including information about the spread of viral (disease or otherwise) processes between individuals in the network. We argue that the dynamics of these processes should be coupled with those of the network evolution in order to improve downstream inference and develop experimental and observational studies --- we do so by studying a class of stochastic epidemic models that are represented by a continuous-time Markov chain such that disease transmission is constrained by the contact network structure, and network evolution is in turn influenced by individual disease statuses. When aiming at estimating causal effect we couple this dynamic modeling with a study of the violation of classical no-interference assumptions, meaning that the treatment of one individuals might affect the outcomes of another. To make interference tractable, we consider a known network that describes how interference may travel. We discuss two settings: (1) design of experiments under known network interference and (2) an observational setting where the radius (and intensity) of the interference experienced by a unit is unknown and can depend on different sub-networks of those treated and untreated that are connected to this unit. In the former we propose an efficient design that leads to the naive difference in means estimator being consistent while in the second we show that under mild regularity conditions, an inverse weighted estimator is consistent, asymptotically normal and unbiased for the average treatment effect on the treated.The back-reaction problem in quantum foundations and gravity
Jonathan Oppenheim University College London
We consider two interacting systems when one is treated classically while the other remains quantum. Despite several famous no-go arguments, consistent dynamics of this coupling exist, and its most general form can be derived. We discuss the application of these dynamics to the foundations of quantum theory, and to the problem of understanding gravity when space-time is treated classically while matter has a quantum nature.
The talk will be informal and I'll review and follow on from joint work with Isaac Layton, Andrea Russo, Carlo Sparaciari, Barbara Šoda & Zachary Weller-Davies
https://arxiv.org/abs/2208.11722
https://arxiv.org/abs/2203.01982
https://arxiv.org/abs/1811.03116Zoom link: https://pitp.zoom.us/j/92520708199?pwd=WUowdnd4Z0k3dlU2YjVmVlAva3Q0UT09