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In compact astrophysical objects, such as neutron star magnetospheres, black-hole accretion disk coronae and jets, the main energy reservoir is the magnetic field. The plasma processes such as magnetic reconnection and turbulence govern the extraction of that energy, which is then deposited into heat and accelerated particles and, ultimately, the observed emission. To understand what we observe, we first need to describe from first principles how these processes operate in violent regimes applicable to certain classes of compact objects, where radiative drag and pair production/annihilation play a significant role. As a specific example, I will briefly cover our state-of-the-art understanding of one of these processes — magnetic reconnection — and present the first self-consistent simulations of QED-mediated reconnection in application to neutron star magnetospheres and explain how it helps us understand the observed gamma-ray emission from these objects. I will also talk about the future prospects of this area of research; QED-mediated plasma processes also take place in a variety of other astrophysical objects, such as the accretion disk coronae in X-ray binaries, coalescing neutron stars shortly before their merger, and short X-ray bursts in magnetars.

In her December 2 Perimeter Public Lecture webcast, Hallberg will explore examples of emergent phenomena and demonstrate how we can tackle these problems using quantum information to filter the most relevant data. By advancing research in this field, we hope to seed advances with applications from medical equipment and new materials to efficient energy generation, transportation, and storage.

I will discuss challenges of quantum gravity, highlighting conceptual, methodological as well as phenomenological aspects. Focusing on asymptotically safe quantum gravity, I will review recent progress in addressing key theoretical challenges using continuum and lattice methods. Furthermore, I will explain how the high predictive power of the asymptotically safe fixed point for quantum gravity and matter might allow us to explain fundamental properties of our universe, for example its dimensionality. Finally, I will point out possible connections between different approaches to quantum gravity, and how these connections might help us formulating a fundamental description of nature.

In string compactifications the roles of physics and geometry are intrinsically intertwined. While the goals of these 4-dimensional effective theories are physical, the path to those answers frequently leads to cutting-edge challenges in modern mathematics. In this talk, I will describe recent progress in characterizing the geometry of Calabi-Yau manifolds in terms their description as elliptic fibrations. This description has remarkable consequences for the form of the string vacuum space and the properties of string effective theories, including particle masses and couplings.

I will review the numerical approach to testing gauge/gravity duality using matrix models. This will lead to a summary of recent results from the BFSS, BMN and Berkooz-Douglas matrix models and a strong non-perturbative test of gauge/gravity duality.

One of the puzzles that the newly data-rich fields of cosmology and astrophysics are most advantaged to tackle is the nature of the dark sector.  In particular, a dark sector that thermalizes with the SM bath at some epoch has present-day observable properties that are directly tied to early-universe interactions. In this talk I survey some recent work on detecting different types of thermal dark particles by leveraging different cosmological and astrophysical datasets.  I discuss the utility of each of these different probes, the implication for particle theories, and prospects for the future. 

Monitored quantum dynamics has attracted much research attention recently. Environmental monitoring typically leads to the decoherence of a quantum system. We explore the effect of energy-level decoherence in quench dynamics. In particular, we consider the linear quench across quantum critical phase transitions under the influence of decoherence. Due to the critical slowing down, the system will necessarily fall out of equilibrium in the vicinity of the critical point within a time scale known as the freeze-out time. The freeze-out time will scale with the quench rate following the Kibble-Zurek scaling. In the presence of decoherence, we found a new scaling behavior differed from the Kibble-Zurek scaling. We demonstrated our findings in the critical quench between 2D Chern insulator and trivial insulator. We show that the new scaling behavior can be justified from the behavior of Hall conductivity across the quantum quench.

A priori, there exists no preferential temporal direction as microscopic physical laws are time-symmetric. Still, the second law of thermodynamics allows one to associate the 'forward' temporal direction to a positive variation of the total entropy produced in a thermodynamic process, and a negative variation with its 'time-reversal' counterpart.
This definition of a temporal axis is normally considered to apply in both classical and quantum contexts. Yet, quantum physics admits also superpositions between forward and time-reversal processes, thereby seemingly eluding conventional definitions of time's arrow. In this talk, I will demonstrate that a quantum measurement of entropy production can distinguish the two temporal directions, effectively projecting such superpositions of thermodynamic processes onto the forward (time-reversal) time-direction when large positive (negative) values are measured.
Remarkably, for small values (of the order of plus or minus one), the amplitudes of forward and time-reversal processes can interfere, giving rise to entropy-production distributions featuring a more or less reversible process than either of the two components individually, or any classical mixture thereof.
Finally, I will extend these concepts to the case of a thermal machine running in a superposition of the heat engine and the refrigerator mode, illustrating how such interference effects can be employed to reduce undesirable fluctuations.

I will show that quasinormal modes of black holes could be used to investigate quantum gravity or modified gravity in specific situations. Some general comments about isospectrality will also be made. Finally a few other quantum gravity phenomena associated with black holes will be underlined.

Abstract: Gamma-ray bursts (GRBs) associated with gravitational wave events are, and will likely continue to be, viewed at a much larger inclination than GRBs without gravitational wave detections.  Viewing GRBs and their afterglows at large inclination can massively affect the observed electromagnetic emission, as dramatically demonstrated by the binary neutron star merger event GW170817.  Analyzing this event and future ones requires an extension of the common GRB afterglow models which typically assume emission from a structureless (top-hat) jet viewed on-axis. I will review the evidence for inclination effects in GRB afterglows, and present a characterization of afterglows viewed at all angles from jets with and without structure. We find new closure relations for off-axis structured jets: the slope of the light curve is found in many cases to be a simple function of the inclination angle. With our theoretical tools in hand I will discuss new candidate kilonova events found in the GRB archive, showing features very similar to GW170817. Finally I will discuss our numerical model to calculate synthetic light curves and spectra, publicly available as the open source Python package afterglowpy, and the steps needed to improve our capabilities for the next LIGO observing run.