Format results

Talk

Welcome and Opening Remarks
Niayesh Afshordi University of Waterloo

Quantum Gravity and its connection to observations
Astrid Eichhorn University of Southern Denmark


The Spacetime of Acceleration
Ruth Gregory King's College London

What is the simplicity of the early universe trying to tell us?
Latham Boyle Perimeter Institute for Theoretical Physics

Are we considering enough? Inclusivity in Quantum Gravity and Cosmology
Jarita Holbrook University of Edinburgh


Emergent Metric SpaceTime from the BFSS Matrix Model
Robert Brandenberger McGill University  Department of Physics


Quantization of causal diamonds in 2+1 dimensional gravity
Rodrigo Andrade E Silva University of Maryland, College Park

Magnetar Eruptions and Electromagnetic Fireworks
Jens Mahlmann Princeton University

An Asymptotic Framework for Gravitational Scattering
Sam Gralla University of Arizona

On the computation of Poisson brackets in field theories
Fernando Barbero Spanish National Research Council (CSIC)



The spherical ejecta of AT2017gfo
Albert Sneppen Niels Bohr Institute


Mysteries of fast radio bursts
Dongzi Li California Institute of Technology (Caltech)

Quantum BergmannKomar group, U(1)^3 quantum gravity and loop quantum gravity
Thomas Thiemann University of ErlangenNuremberg

Quantum Spacetime in the Cosmos: From Conception to Reality
On Demand Recording: https://pirsa.org/C23035
The nature of space and time is one of the most foundational mysteries in both Physics and Philosophy. At the heart of this mystery are the two most successful theories of nature: Einstein's theory of relativity, an elegant and precise description of the geometry of our universe on large scales, and Quantum Mechanics, outlining accurate laws of interaction in the subatomic world. But these two great triumphs of 20th century physics remain inherently inconsistent, contradictory in their most basic principles, such as locality and causality. Nonetheless, the experimental domains or natural phenomena where these contradictions become manifest have remained elusive, and it is not clear that a century of theoretical investigation into quantum gravity is anywhere close to being verified in nature.
Arguably, this disconnect is our greatest and most foundational challenge in the history of Physics; despite groundbreaking progress in both theory and observations of quantum spacetimes, these two endeavours are moving farther apart. Successfully responding to this centuryold challenge could require rethinking the epistemology of fundamental physics. While physicists are trained to push the frontiers of knowledge, developing a grand vision of the arch of history, and where we are (or should be) heading is a more interdisciplinary endeavor, requiring insights from theory and observations, but also philosophy and history.
We plan a focused, interactive, and highly interdisciplinary workshop, involving the world’s best theorists, observers, experimentalists, and philosophers, within a supportive, inclusive, and diverse environment, in order to kick start a long term initiative that might be our best bet to make significant progress towards uncovering the quantum nature of spacetime.Sponsorship provided by:
Territorial Land AcknowledgemenPerimeter Institute acknowledges that it is situated on the traditional territory of the Anishinaabe, Haudenosaunee, and Neutral peoples.
Perimeter Institute is located on the Haldimand Tract. After the American Revolution, the tract was granted by the British to the Six Nations of the Grand River and the Mississaugas of the Credit First Nation as compensation for their role in the war and for the loss of their traditional lands in upstate New York. Of the 950,000 acres granted to the Haudenosaunee, less than 5 percent remains Six Nations land. Only 6,100 acres remain Mississaugas of the Credit land.
We thank the Anishinaabe, Haudenosaunee, and Neutral peoples for hosting us on their land.

Quantization of causal diamonds in 2+1 dimensional gravity
Rodrigo Andrade E Silva University of Maryland, College Park
We develop the reduced phase space quantization of causal diamonds in $2+1$ dimensional gravity with a nonpositive cosmological constant. The system is defined as the domain of dependence of a spacelike topological disk with fixed (induced) boundary metric. By solving the constraints in a constantmeancurvature time gauge and removing all the spatial gauge redundancy, we find that the phase space is the cotangent bundle of $Diff^+(S^1)/PSL(2, \mathbb{R})$, i.e., the group of orientationpreserving diffeomorphisms of the circle modulo the projective special linear subgroup. Classically, the states correspond to causal diamonds embedded in $AdS_3$ (or $Mink_3$ if $\Lambda = 0$), with a fixed corner length, that have the topological disk as a Cauchy surface. Because this phase space does not admit a global system of coordinates, a generalization of the standard canonical (coordinate) quantization is required  in particular, since the configuration space is a homogeneous space for a Lie group, we apply Isham's grouptheoretic quantization scheme. The Hilbert space of the associated quantum theory carries an irreducible unitary representation of the $BMS_3$ group, and can be realized by wavefunctions on a coadjoint orbit of Virasoro with labels in irreducible unitary representations of the corresponding little group. A surprising result is that the twist of the diamond boundary loop is quantized in terms of the ratio of the Planck length to the corner length.
Zoom link: https://pitp.zoom.us/j/94369372201?pwd=NWNsYno3RmZIWUx0LytWZ09PVDVVQT09

Magnetar Eruptions and Electromagnetic Fireworks
Jens Mahlmann Princeton University
Highly magnetized neutron stars are a source of extreme transients observed in different bands, like the fast radio burst (FRB) and associated hard Xray burst from the Galactic magnetar SGR 1935+2154. The origin of such outbursts, hard Xrays on the one hand and millisecond duration FRBs on the other hand, is still unknown. We present a global model for various kinds of such magnetar outbursting activities. Crustal surface motions are expected to twist the inner magnetar magnetosphere by shifting the frozenin footpoints of magnetic field lines. We discuss criteria for the development of various instabilities of 3D twisted flux bundles in the forcefree dipolar magnetospheres and compare their energetic properties to observations of magnetar Xray flares. We then review a recently developed FRB generation mechanism in the outer magnetosphere of a magnetar. The strong magnetic pulse induced by a magnetar flare collides with the current sheet of the magnetar wind, compresses and fragments it into a selfsimilar chain of magnetic islands. Timedependent plasma currents created during their collisions produce relatively narrowband GHz emission with luminosities sufficient to explain bright extragalactic FRBs.
Zoom ink: https://pitp.zoom.us/j/96469987183?pwd=N1UzVkh6RGZUeWV6TFZJLzk0M3VWZz09

An Asymptotic Framework for Gravitational Scattering
Sam Gralla University of Arizona
Gravitational scattering provides valuable insight into classical dynamics and is likely of fundamental importance in quantum gravity. However, a complete framework for gravitational scattering does not yet exist. The lack of a clear framework hinders progress; for example, different groups have reported different results for the loss of angular momentum in postMinkowskian scattering. In this talk I will report on recent work 2303.17124 with Compere and Wei constructing a general framework for classical gravitational scattering of finitesized massive bodies in four spacetime dimensions. We formulate assumptions and definitions such that the five asymptotic regions (past/future timelike/null infinity and spatial infinity) share a single BondiMetznerSachs (BMS) group of symmetries and associated charges and derive global conservation laws stating that the total change in charge is balanced by the corresponding radiative flux. Our assumptions are compatible with all known properties of scattering spacetimes, including certain logarithmic corrections that invalidate common falloff assumptions. Among the new implications are rigorous definitions for quantities like initial/final spin, scattering angle, and impact parameter in multibody spacetimes, without the use of any preferred background structure. We show that spin is supertranslationinvariant, while impact parameter is not. To complement these derivations I will emphasize a helpful "puzzle piece" diagram that faithfully represents all five asymptotic regions, illustrating their roles in the scattering problem.
Zoom link: https://pitp.zoom.us/j/94358515412?pwd=cUFocVNjQ1pqUmp4MDN0RmRLbjE0QT09

On the computation of Poisson brackets in field theories
Fernando Barbero Spanish National Research Council (CSIC)
I will discuss several issues related to the computation of Poisson brackets in field theories. I will show that by choosing appropriate functional spaces as configuration manifolds, it is possible to avoid the use of distributions. This is relevant, for instance, in the context of Loop Quantum Gravity, where the basic holonomy/flux variables play a central role. I will illustrate the main ideas by using simple examples based on Sobolev spaces.
Zoom link: https://pitp.zoom.us/j/92794475242?pwd=T2Fjbk1lTXRCNnBxVDZabnJqWlAzUT09

Monarch Migration of Carrollian Particles on the Black Hole Horizon
David Kubiznak Charles University
After discussing the basics of Carrollian physics, we shall revisit the motion of massless particles with anyonic spin in the black hole horizons. As recently shown, such particles can move within the horizon of the black hole due to the coupling of charges associated with a 2parametric central extension of the 2dimensional Carroll group to the magnetic field around the black hole  the so called "anyonic spinHall effect". We shall study several examples of such motions. Of these, the most interesting is the motion in misaligned (asymptotically uniform) magnetic field around Kerr, which results in a time dependent motion of Carrollian particles that is reminiscent of "monarch migration".
Zoom link: https://pitp.zoom.us/j/97094479078?pwd=SHN6NEU5aE93OXVQYk9aWTVOdzRRUT09

Puzzles in the Quantum Gravity Landscape: viewpoints from different approaches
Unraveling the quantum nature of gravity is one of the most pressing problems of theoretical physics. Several ideas have been put forward and resulted in a number of theories of quantum gravity. While these theories have explored different facets of the “quantum gravity landscape”, all viable approaches should ultimately make contact with observations, and answer exciting questions in cosmology and blackhole physics.
Sharing knowledge, exchanging ideas, and building a dictionary between different theories are crucial steps toward answering these questions, efficiently contrasting different theories, and ultimately reaching a deeper understanding of our Universe.
This conference will contribute to these goals by bringing together leading experts in different approaches to quantum gravity, gravitational effective field theory, blackhole physics, and cosmology. We will focus on specific puzzles in quantum gravity and their resolutions within different approaches. The conference will be highly interactive, with plenty of time to discuss common problems, understand the big picture, and develop novel connections between fields.Confirmed Speakers and Panelists:
 Abhay Ashtekar, Penn State University
 Robert Brandenberger, McGill University
 Luca Buoninfante, Nordita
 Xavier Calmet, University of Sussex
 Francesco di Filippo, Kyoto University
 Bianca Dittrich, Perimeter Institute
 John Donoghue, University of Massachusetts
 Astrid Eichhorn, CP3origins
 Ruth Gregory, King's College
 Lavinia Heisenberg, Heidelberg University
 Bob Holdom, University of Toronto
 Benjamin Knorr, Nordita
 Renate Loll, Radboud University Nijmegen
 Rob Myers, Perimeter Institute
 Miguel Montero, Harvard
 Sabrina Pasterski, Perimeter Institute
 Fernando Quevedo (tbc), Cambridge
 Mairi Sakellariadou, King's College
 Lee Smolin, Perimeter Institute
 Sumati Surya, Raman Research Institute
 Pedro Vieira, Perimeter Institute
Registration will open soon.
Territorial Land Acknowledgement
Perimeter Institute acknowledges that it is situated on the traditional territory of the Anishinaabe, Haudenosaunee, and Neutral peoples.
Perimeter Institute is located on the Haldimand Tract. After the American Revolution, the tract was granted by the British to the Six Nations of the Grand River and the Mississaugas of the Credit First Nation as compensation for their role in the war and for the loss of their traditional lands in upstate New York. Of the 950,000 acres granted to the Haudenosaunee, less than 5 percent remains Six Nations land. Only 6,100 acres remain Mississaugas of the Credit land.
We thank the Anishinaabe, Haudenosaunee, and Neutral peoples for hosting us on their land.

ParityViolation in Gravity: New Constructions and Inflationary Signals
Cyril CrequeSarbinowski Flatiron Institute
I will talk about new constructions to the parityviolating sector of gravity that can yield large observables, in particular those from inflation. Within this framework, I will demonstrate the potential for seeking gravitational parityviolation in uncharted regions of parameter space and give hints to novel methods of probing baryogenesis. I will also comment on a few interesting theoretical aspects regarding inflationary correlators.
Zoom link: https://pitp.zoom.us/j/95924890817?pwd=MkRyWmV2a3g1dndPNFhoVlQvb3Ixdz09

The spherical ejecta of AT2017gfo
Albert Sneppen Niels Bohr Institute
The geometry of kilonovae is a key diagnostic of the physics of merging neutron stars with current hydrodynamical merger models typically showing aspherical ejecta. Previously, Sr II was identified in the spectrum of the only wellstudied kilonova AT2017gfo, associated with the gravitational wave event GW170817. In this talk, we show that combining the strong Sr II P Cygni absorptionemission spectral feature and the blackbody nature of the kilonova spectrum, to determine that the kilonova is highly spherical at early epochs. Line shape analysis combined with the known inclination angle of the source also shows the same sphericity independently. The nearspherical geometry suggests early spectra of kilonovae may provide excellent precision cosmic distance measurements using the Expanding Photosphere Method.
Zoom link: https://pitp.zoom.us/j/97287055430?pwd=bFVyeTRuZHVLcGlDdnhlK1d0OWE1Zz09

From Gaussian thermal partition functions to multi loop conformal graphs
I will discuss a recently observed connection between Gaussian thermal partition functions in d=2L+1 dimensions and Lloop conformal graphs in D=4. While the origin of such a connection is still unclear, I will argue that it offers some interesting perspectives in quantum field theory and in mathematics.
Zoom link: https://pitp.zoom.us/j/98795029694?pwd=aGdSdWtDQ1VqbzFvSWE4SkM5c3lJUT09

Mysteries of fast radio bursts
Dongzi Li California Institute of Technology (Caltech)
Fast Radio Bursts (FRBs) are extremely energetic, millisecondduration radio bursts coming outside our galaxy. The burst arrival time at different frequencies implies the number of electrons it has encountered in the foreground. Therefore, FRB is considered a promising new cosmology probe. The uncertainty of the circumburst environment is one of the biggest concerns regarding its potential as a probe. In this talk, I will review the current understanding of the FRB progenitor and the recent study of the circumburst environment. I will also discuss the many remaining mysteries, including the seemingly diverse nature of the sources, the magnetoenvironment, and the 16day periodicity I found with one source. With the current and upcoming instruments, there will be more FRBs with orders of magnitude better spatial resolution detected in the next few years. The result will be an explosion of opportunity for understanding the burst origin and probing cosmic matter distribution at various spatial scales.
Zoom link: https://pitp.zoom.us/j/92030175800?pwd=dWlGVjV0Qnh5bGhLMk1pd01yRmNKQT09

Quantum BergmannKomar group, U(1)^3 quantum gravity and loop quantum gravity
Thomas Thiemann University of ErlangenNuremberg
In any approach to quantum gravity, the quantum representation theory of the "algebra" of Cauchy hypersurface deformations plays a crucial role. Its faithful implementation is a key step towards constructing a valid theory of quantum gravity as it ensures quantum spacetime diffeomorphism covariance. Bergmann and Komar were the first to consider the possibilty of a corresponding quantum "group". Its construction is mathematically challenging in more than 1+1 spacetime dimensions because one leaves the realm of Lie algebras and Lie groups. After an introduction to these concepts, we show that the Bergmann Komar "group" can indeed be faithfully implemented in a weakly selfinteracting truncation of 3+1 quantum gravity with two propagating polarisations. We then discuss possible implications for the actual, untruncated theory.
Zoom link: https://pitp.zoom.us/j/91488383205?pwd=bkxGS0huMGNEYXc3Y2FJSGZHQ0pqQT09