# Video Library

Since 2002 Perimeter Institute has been recording seminars, conference talks, public outreach events such as talks from top scientists using video cameras installed in our lecture theatres.  Perimeter now has 7 formal presentation spaces for its many scientific conferences, seminars, workshops and educational outreach activities, all with advanced audio-visual technical capabilities.

Recordings of events in these areas are all available and On-Demand from this Video Library and on Perimeter Institute Recorded Seminar Archive (PIRSA)PIRSA is a permanent, free, searchable, and citable archive of recorded seminars from relevant bodies in physics. This resource has been partially modelled after Cornell University's arXiv.org.

Accessibly by anyone with internet, Perimeter aims to share the power and wonder of science with this free library.

## A voyage through undulating dark matter and the GUTs of u(48)

Tuesday Dec 15, 2020
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This talk will be split into two distinct halves: The first half will be based on the paper arxiv:2007.03662 and suggest that an interplay between microscopic and macroscopic physics can lead to an undulation on time scales not related to celestial dynamics. By searching for such undulations, the discovery potential of light DM search experiments can be enhanced.

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## Cosmological tensions and how to ease them

Tuesday Dec 15, 2020
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Tensions between measurements in the early and the late universe could be the first hint of new physics beyond the cosmological standard model. In particular, the clustering of large scale structure and the current value of the Hubble parameter show intriguing discrepancies between measurements in the early and late universe. In this talk, I review the most common ways of easing these two tensions and focus specifically on parameter extensions and various models of dark matter, such as warm dark matter, cannibalistic dark matter, dark matter interactions, and dark radiation.

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## Generalized entropy in topological string theory

Tuesday Dec 15, 2020
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The Ryu Takayanagi formula identifies the area of  extremal surfaces in AdS with the entanglement entropy of the boundary CFT. However the bulk microstate interpretation of the extremal area remains mysterious. Progress along this direction requires understanding how to define entanglement entropy in the bulk closed string theory. As a toy model for AdS/CFT, we study the entanglement entropy of closed strings in the topological A model in the context of Gopakumar Vafa duality.

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## Decoherence vs space-time diffusion: testing the quantum nature of gravity

Monday Dec 14, 2020

Consistent dynamics which couples classical and quantum systems exists, provided it is stochastic. This provides a way to
study the back-reaction of quantum systems on classical ones and has recently been explored in the context of quantum fields back-reacting

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## Self-testing Bell inequalities from the stabiliser formalism and their applications

Friday Dec 11, 2020
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I will introduce a tool to construct self-testing Bell inequalities from the stabiliser formalism and present two applications in the framework of device-independent certification protocols. Firstly, I will show how the method allows to derive Bell inequalities maximally violated by the family of multi-qubit graph states and suited for their robust self-testing.

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## Dynamics and observational traces of cosmological ultra-supercooled phase transitions

Friday Dec 11, 2020
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In recent years, there has been growing interest in cosmological first-order phase transitions in view of gravitational wave observations with space interferometers such as LISA. However, there is only limited understanding on the bubble dynamics and the gravitational wave signals arising from ultra-supercooled transitions (in which the released energy dominates the plasma energy, i.e., near-vacuum transitions), due to the highly relativistic nature of the transition.

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## Self-torque and frame nutation in binary black hole simulations

Thursday Dec 10, 2020

We investigate the precession of the spin of the smaller black hole in binary black hole simulations. By considering a sequence of binaries at higher mass ratios, we approach the limit of geodetic precession of a test spin. This precession is corrected by the self-torque'' due to the smaller black hole's own spacetime curvature. We find that the spins undergo spin nutations which are not described in conventional descriptions of spin precession, an effect that has been noticed previously in simulations.

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## Can we think time-symmetrically about causation?

Thursday Dec 10, 2020
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We often say that quantum mechanics allows to calculate the probability of future events. In fact, quantum mechanics does not discriminate between predicting the future or postdicting the past. I will present the results of a recent work by Rovelli, Donà and me, where we address the apparent tension between the time symmetry of elementary quantum mechanics and the intrinsic time orientation of the formulations of quantum theory used in the quantum information and foundations communities.

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## Exploring alternatives to quantum nonlocality

Wednesday Dec 09, 2020
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In recent years, it has become increasingly well-known that nearly all the major no-go theorems in quantum foundations can be circumvented by violating a single assumption: the hidden variables (that determine the outcomes) are uncorrelated with the measurement settings. A hidden-variable theory that violates this assumption can be local, separable, non-contextual and have an epistemic quantum state. Such a theory would be particularly well-suited to relativistic contexts. Are such theories actually feasible?

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## Symmetries, graph properties, and quantum speedups

Wednesday Dec 09, 2020
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Aaronson and Ambainis (2009) and Chailloux (2018) showed that fully symmetric (partial) functions do not admit exponential quantum query speedups. This raises a natural question: how symmetric must a function be before it cannot exhibit a large quantum speedup? In this work, we prove that hypergraph symmetries in the adjacency matrix model allow at most a polynomial separation between randomized and quantum query complexities.

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## Lectures On-Demand

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