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Quantum field theory intertwines continuous and discrete structures. On the discrete side, combinatorics plays a central role in describing and understanding its expansions and models. This lecture series focuses on the combinatorial aspects of quantum field theory. In the first part, we explore analytic combinatorics techniques, inspired by QFT, for the enumeration of graphs. These methods turn out to be surprisingly powerful in addressing deep questions in algebraic geometry, topology, and statistical models on graphs. In the second part, we turn to discrete structures arising in perturbative expansions of QFT. We study these from a modern combinatorics viewpoint, using tools such as Lorentzian polynomials and generalized permutahedra to better understand the mathematical objects at the heart of quantum field theory. For updates visit: https://michaelborinsky.com/combqft.html This course is offered by the University of Waterloo's Department of Combinatorics & Optimization; UW students can enroll through Quest. Lectures will be held at Perimeter Institute, 31 Caroline St N, Waterloo. Students will need to sign in and out of Perimeter each day. Note room change on Sept 25 and Oct 2, and no classes week of October 13.

*Scroll down to Registration and Enrollment to participate.* **Structure:** We will discuss 8 papers which had huge impact in physics. One week Instructor Pedro Vieira will discuss a paper; students should read it beforehand. One week later students discuss recent papers referring to that paper (20 min each student, ~ 3 presentations; at the end of the class Pedro will grade the presentations based on “Physics”, “Presentation”, “Question handling”; and give comments). By the end of the course, students will have explored a vast set of topics in theoretical physics — spotting potential gaps to be fixed — sharpened their presentation skills through steady practice, and sparked cross-disciplinary conversations through our shared physics language. *Familiarity with Quantum Field Theory and General Relativity is assumed.* **The papers:** Sept 12 & 19: On the Quantum Correction for Thermodynamic Equilibrium, Wigner, 1932 Topic: Quantum Mechanics Sept 22 & 29: Existence theorem for certain systems of nonlinear PDEs, Foures-Bruhat, 1952 Topic: General relativity Oct 3 & 10: The Renormalization Group and the Epsilon Expansion, Wilson and Kogut, 1973 Topic: Quantum Field Theory **Oct 10 (EXTRA)** & 17: More about the Massive Schwinger Model, Coleman, 1976 Topic: 2D Quantum Field Theory Oct 20 & 27: A sequence of approximated solutions to the S-K model for spin glasses, Parisi, 1980 Topic: Statistical Mechanics Oct 31 & Nov 7: Quantum Field Theory and the Jones Polynomial, Witten, 1988 Topic: Topological Quantum Field Theory Nov 10 & 17: Exactly Solvable Field Theories of Closed Strings, Brezin, Kazakov, 1989 Topic: 2D Quantum Gravity Nov 21 & Nov 28: Unpaired Majorana fermions in quantum wires, Kitaev, 2000 Topic: Quantum Matter/Quantum Information **Schedule:** This is a Friday / Monday alternating week schedule from 915am-1045am. **Exceptions:** There will be an afternoon session at 130pm on Friday October 10 to avoid the Thanksgiving holiday. **Location & Building Access:** Alice Room, 3rd Floor, Perimeter Institute, 31 Caroline St N, Waterloo Participants who do not have an access card for Perimeter Institute must sign in at the security desk before each session. For information on parking or accessibility please contact academic@perimeterinstitute.ca. **Registration and Enrollment:** Please sign-up here: https://forms.office.com/r/nDQ6SDxSR4 **Zoom Link** https://pitp.zoom.us/j/95238695187?pwd=G6EjbywTpOagSxpbMZtgznxmuwFFBp.1

This is a theoretical physics course that aims to review the basics of theoretical mechanics, special relativity, and classical field theory, with the emphasis on geometrical notions and relativistic formalism, thus setting the stage for the forthcoming courses in Quantum Mechanics, and Quantum Field Theory in particular, as well as in General Relativity and Quantum Gravity. Instructor: Aldo Riello Students who are not part of the PSI MSc program should review enrollment and course format information here: https://perimeterinstitute.ca/graduate-courses

Charting the Future Symposium: Big questions in particle physics, strong gravity, and cosmology over the next 25 years

Join us for a special symposium celebrating Perimeter’s 25th anniversary. This event offers a unique opportunity to unite Perimeter alumni and friends in the fields of cosmology, particle physics, and strong gravity with our extended community, reflect on a quarter-century of discovery, and look ahead to the challenges and opportunities that will shape the next 25 years of fundamental physics.

Over the past quarter-century, we have witnessed transformative advances across our fields. In particle physics, the discovery of the Higgs boson crowned decades of effort, while precision experiments continue to probe the Standard Model and search for new physics. In strong gravity, the direct detection of gravitational waves has opened a new observational window onto black holes, neutron stars, and the very fabric of spacetime. In cosmology, precision measurements of the cosmic microwave background and large-scale structure have revolutionized our understanding of the universe’s origins and evolution, even as dark matter and dark energy remain profound mysteries.

As we look to the future, a new generation of experiments, observations, and theoretical ideas promises to drive further revolutions. From uncovering physics beyond the Standard Model to probing the nature of spacetime and the earliest moments of the cosmos, the next 25 years are poised to be as transformative as the last.

This symposium will bring together leading researchers, young scientists, alumni, and friends to celebrate past achievements, and imagine the discoveries yet to come. We invite you to be part of this landmark event at Perimeter Institute, as we honor the spirit of curiosity, ambition, and collaboration that has defined our journey so far — and will carry us forward.

 

Invited Speakers

• Haipeng An (Tsinghua University)
• Masha Baryakhtar (University of Washington)
• Brian Batell (University of Pittsburgh)
• Laura Bernard (Observatoire de Paris)
• Richard Bond (CITA)
• Pablo Bosch Gomez (Utrecht University)
• Latham Boyle (University of Edinburgh)
• Patrick Brady (University of Wisconsin-Milwaukee)
• Joe Bramante (Queen's University)
• Savas Dimopoulos (Perimeter Institute)
• Adrienne Erickcek (University of North Carolina at Chapel Hill)
• Stefania Gori (UC Santa Cruz)
• Chad Hanna (Pennsylvania State)
• Renée Hložek (University of Toronto)
• Yoni Kahn (University of Toronto)
• Vicky Kaspi (McGill University)
• Gordan Krnjaic (Fermilab)
• Ian Low (Northwestern University)
• Mathew Madhavacheril (University of Pennsylvania)
• David Morissey (TRIUMF)
• Moritz Münchmeyer (University of Wisconsin-Madison)
• Ue-Li Pen (CITA, Perimeter Institute)
• Will Percival (Perimeter Institute)
• Maxim Pospelov (University of Minnesota)
• Josef Pradler (Austrian Academy of Sciences)
• Daniel Siegel (University of Greifswald)
• Nils Siemonsen (Princeton University)
• Carlos Wagner (University of Chicago)
• Huan Yang (Tsinghua University)
• Matias Zaldarriaga (IAS)

 

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Organizing Committee
Asimina Arvanitaki
Luis Lehner
Sergey Sibiryakov
Kendrick Smith

 

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QIQG 2025: Quantum Information in Quantum Gravity

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Scientific Organizers

Luca Ciambelli (Perimeter Institute)
Rob Myers (Perimeter Institute)
Chris Waddell (Perimeter Institute)
Beni Yoshida (Perimeter Institute)

Detector operators, of which the average null energy operator provides the most famous example, arise as direct theoretical models of asymptotic measurements in collider experiments. In QFT, detector operators are expressed in terms of "light-ray operators", whose correlation functions provide an interesting class of non-perturbatively well-defined observables. There has recently been renewed interest in detector operators coming from three distinct directions: In CFTs, there has been progress understanding the space of light-ray operators, their organization into Regge trajectories, and their appearance in Lorentzian operator product expansions. In perturbative QFT and gravity, borrowing techniques from the study of scattering amplitudes, there has been progress understanding multi-point correlation functions of detector operators, in particular, their function space and singularities. Finally, in particle physics, there have recently been direct measurements of correlation functions of detector operators in collider experiments, enabling measurements of their scaling behavior and the structure of multi-point correlators of light-ray operators in QCD. In this mini-course I will give an introduction to the theory of light-ray/ detector operators, their correlators, and their applications in particle phenomenology, and provide an overview of the recent progress in the directions mentioned above. Throughout, I will attempt to highlight the different perspectives and motivations for studying these operators, coming from the CFT, amplitudes and phenomenological communities. I will conclude with a discussion of open problems in both theory and phenomenological applications, as well as highlighting areas where theoretical developments could have an impact on real world applications at colliders. Join live sessions via Zoom link: https://pitp.zoom.us/j/96935592330?pwd=NNtf7839TThLFEWIzdH7fYxNYksyYr.1 View all past talks on PIRSA: https://pirsa.org/c25035

What is time? Is it fundamental or emergent? This question lies at the foundation of contemporary physics and provides a key to unlocking some of its most challenging open problems, from quantum gravity to cosmology. The quest to understand time extends beyond the realm of physics, providing a privileged standpoint to address questions in diverse fields such as philosophy, mathematics, and computer science.

In this conference, we explore the nature of time from many different perspectives. This is the occasion to honor Perimeter’s “Master of Time,” Lee Smolin, and to celebrate his seminal scientific contributions. Lee Smolin is a founding faculty member of Perimeter Institute and a primary inspiration behind its spirit and design. This is an opportunity to journey back in time to the origins of some of the groundbreaking initiatives that Lee helped develop, and to look forward to future developments inspired by his achievements. The conference focuses on time but also on the foundations of quantum mechanics and the quest for quantum gravity, particularly Loop Quantum Gravity, of which Lee Smolin is a co-creator. In the spirit of Lee Smolin, the conference celebrates the interdisciplinary nature of the journey toward quantum gravity, with contributions from physics, mathematics, computer science, and philosophy.

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Scientific Organizers
Laurent Freidel (Perimeter Institute)
Maïté Dupuis (Perimeter Institute)
Dongxue Qu (Perimeter Institute)
Francesca Vidotto (Western University)

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Speakers

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Credit: Artwork by Kaća Bradonjić

 

This course in Cosmology provides a theoretical overview of the standard cosmological model. Key topics include the FRW metric and the homogeneous universe, the thermal history of the universe (with an emphasis on the hot Big Bang and equilibrium thermodynamics), inflation and scalar field dynamics, along with selected aspects of cosmological perturbation theory (time permitting). Instructor: Neal Dalal/Ghazal Geshnizjani Students who are not part of the PSI MSc program should review enrollment and course format information here: https://perimeterinstitute.ca/graduate-courses

Can the effectiveness of a medical treatment be determined without the expense of a randomized controlled trial? Can the impact of a new policy be disentangled from other factors that happen to vary at the same time? Questions such as these are the purview of the field of causal inference, a general-purpose science of cause and effect, applicable in domains ranging from epidemiology to economics. Researchers in this field seek in particular to find techniques for extracting causal conclusions from statistical data. Meanwhile, one of the most significant results in the foundations of quantum theory—Bell’s theorem—can also be understood as an attempt to disentangle correlation and causation. Recently, it has been recognized that Bell’s result is an early foray into the field of causal inference and that the insights derived from almost 60 years of research on his theorem can supplement and improve upon state-of-the-art causal inference techniques. In the other direction, the conceptual framework developed by causal inference researchers provides a fruitful new perspective on what could possibly count as a satisfactory causal explanation of the quantum correlations observed in Bell experiments. Efforts to elaborate upon these connections have led to an exciting flow of techniques and insights across the disciplinary divide. This course will explore what is happening at the intersection of these two fields. Instructor: Robert Spekkens/Bindiya Arora Students who are not part of the PSI MSc program should review enrollment and course format information here: https://perimeterinstitute.ca/graduate-courses

We will cover the basics of the gauge/gravity duality, including some of the following aspects: holographic fluids, applications to condensed matter systems, entanglement entropy, and recent advances in understanding the black hole information paradox. Instructor: David Kubiznak/Gang Xu Students who are not part of the PSI MSc program should review enrollment and course format information here: https://perimeterinstitute.ca/graduate-courses