Seminar
- !! New time and format !!
- Thursday 12:40-14:00
- Room L1-047
- Talk starts at 12:50, pizza will be served at 12:40.
Schedule Winter 2024
- April 11, 2024
- April 4, 2024
- March 28, 2024
- March 21, 2024
- March 14, 2024
- March 7, 2024
- February 29, 2024
- February 22, 2024
- February 15, 2024
- February 8, 2024
- February 1, 2024
- January 25, 2024
- January 18, 2024: Duncan O'Dell (McMaster University)
- January 11, 2024
Schedule Fall 2023
- December 18, 2023: Joel Hutchinson (University of Basel)
Note special date (Monday)
- December 7, 2023: Javier Reynoso Cordova (University of Alberta)
- November 30, 2023: Alexander Penin (University of Alberta)
- November 23, 2023: Steven Rayan (University of Saskatchewan)
Joint TPI/Math colloquium. Room CAB 239, 4-5 pm
- November 9, 2023: Shinji Mukohyama (Yukawa Institute, Kyoto)
Effective field theory of black hole perturbations with timelike scalar profile
Many dark energy (DE) models are based on a scalar field with timelike gradient. In this talk we begin with a review of the systematic construction of the effective field theory (EFT) describing perturbations around the Minkowski background with a timelike scalar profile and its extension to cosmological backgrounds, i.e. the ghost condensation and the EFT of inflation/DE. If one hopes to learn something about the EFT of DE from black holes (BHs) then one needs to consider BH solutions with timelike scalar profiles. We thus extend the EFT to arbitrary backgrounds. Finally, as an application of the general EFT, we study odd-parity perturbations around a spherically symmetric, static black hole background with a timelike scalar field responsible for DE and compute quasi-normal mode frequencies.
- October 19, 2023: Shiwei Zhang (Flatiron Institute)
Magnetism and superconductivity - insights from computations on the Hubbard model
The Hubbard model is fundamental to quantum many-body physics. Since the discovery of high-temperature superconductivity, it has been a focal point in condensed matter and more recently also in the field of ultracold atoms. The properties of the two-dimensional Hubbard model are often the outcome of a delicate balancing act between multiple competing or co-existing tendencies. This makes accurate computations essential, but also extremely challenging. Through advances in methodologies and the combined use of complementary methods, we are seeing a new era of rapid progress. I will discuss some of these developments, and what they have revealed about the physics of the Hubbard model.
- October 5, 2023: Nikolay Prokof'ev (University of Massachusetts, Amherst)
Bi-polaron superconductivity in the low density limit
It has been assumed for decades that high values of Tc from the electron-phonon coupling are impossible. At weak-to-intermediate coupling strength this result follows from the Migdal-Eliashberg theory, while at strong coupling, when bipolarons form, the transition temperatures are low because of the large effective mass enhancement. However, the latter conclusion was based on numerical solutions of the Holstein model. I will discuss a different model with electron-coupling based on the displacement modulated hopping of electrons and argue that much larger values of the bipolaron Tc can be achieved in this setup. Non-locality of the problem gives rise to small-size, yet relatively light bipolarons, which can be studied by an exact sign-problem-free quantum Monte Carlo approach even in the presence of strong Hubbard and Coulomb potentials. We find that Tc in this model generically and significantly exceeds typical upper bounds based on Migdal-Eliashberg theory or superfluidity of Holstein bipolarons, and, thus, offers a route towards the design of high-Tc superconductors via functional material engineering. Finally, there are indications for even better prospects in systems with non-linear electron-phonon coupling.
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