Physics

During the last 20 years, we have seen a tremendous development in the computational power of our devices. We have by now laptops and phones that are more powerful than the high-profile workstations of a few generations ago. This computational power has already severely impacted our lives and many scientific fields as well, with examples ranging from AI to biophysics. On the other hand, a large class of problems in the study of quantum many-body systems has benefited only marginally from these developments.In the talk, I will review this class of problems, emphasizing the conceptual reason behind the limited impact that traditional computational methods have brought. I will then move on to describe the most promising candidates (in my opinion) to overcome the current situation.

Predicting the outcome of scattering processes of elementary particles in colliders is the central achievement of relativistic quantum field theory applied to the fundamental (non-gravitational) interactions of nature. While the gravitational interactions are too minuscule to be observed in the microcosm, they dominate the interactions at large scales. As such the inspiral and merger of black holes and neutron stars in our universe are now routinely observed by gravitational wave detectors. The need for high precision theory predictions of the emitted gravitational waveforms has opened a new window for the application of perturbative quantum field theory techniques to the domain of gravity. In this talk I will show how observables in the classical scattering of black holes and neutron stars can be efficiently computed in a perturbative expansion using a world-line quantum field theory; thereby combining state-of-the-art Feynman integration technology with perturbative quantum gravity. Here, the black holes or neutron stars are modelled as point particles in an effective field theory sense. Fascinatingly, the intrinsic spin of the black holes may be captured by a supersymmetric extension of the world-line theory, enabling the computation of the far field wave-form including  spin and tidal effects to highest precision. I will review our most recent results at the fifth order in the post-Minkowskian expansion amounting to the computations of hundreds of thousands of four loop Feynman integrals.

---

Zoom link 

We develop a Machine-Learning Renormalization Group (MLRG) algorithm to explore and analyze many-body lattice models in statistical physics. Using the representation learning capability of generative modeling, MLRG automatically learns the optimal renormalization group (RG) transformations from self-generated spin configurations and formulates RG equations without human supervision. The algorithm does not focus on simulating any particular lattice model but broadly explores all possible models compatible with the internal and lattice symmetries given the on-site symmetry representation. It can uncover the RG monotone that governs the RG flow, assuming a strong form of the $c$-theorem. This enables several downstream tasks, including unsupervised classification of phases, automatic location of phase transitions or critical points, controlled estimation of critical exponents, and operator scaling dimensions. We demonstrate the MLRG method in two-dimensional lattice models with Ising symmetry and show that the algorithm correctly identifies and characterizes the Ising criticality.

---

Zoom link

Advanced subjects and complicated applications. Applications to the interacting theories. Appelquist and Carazzone theorem in QED. Decupling of massive degrees of freedom in polynomial higher derivative quantum gravity: mixed diagrams. Non-local theories of quantum gravity. On the possibility of the universal IR limit in quantum gravity

In this talk I will describe recent proposed experimental setups developed to test the quantum nature of gravity and how they can be used to test different quantum theories. After a brief overview of the motivations behind those setups, I will show how, in the context of canonical quantum gravity, one can derive quantum gravitational corrections for an approximate Schrödinger equation for matter fields in a fixed background. The corrections can be non-linear and non-Hermitian, which poses a series of problems. I will focus on the non-Hermitian terms, their interpretation and their possible observational consequences in different scenarios. I will then describe the differences in the pilot-wave approach to quantum gravity, how it offers a natural interpretation for the corrections in terms of the Quantum Equilibrium Hypothesis and a path for deriving the effects of such corrections in tabletop experiments. If there is time, I will comment on the nonlinear modifications of the Schrödinger equations, on a recent attempt to introduce them in the path integral formalism of EFT quantum gravity in a consistent manner (Correlated Worldline Theory) and on their phenomenological consequences.

Basic calculations and basic results. One-loop Feynman diagrams and derivation of the nonlocal form factors for the two-point function. High-energy and low-energy limits. Quadratic decoupling in the IR. Curved-space calculation using the heat-kernel solution. Applications to the fourth-derivative terms in the one-loop effective action of gravity