Physics seminars

Matthias Vigl examines whether the computational scaling strategies behind modern machine learning can benefit particle physics. Empirical scaling laws relate model performance to computing resources and help balance model size against training-data volume. For a fixed dataset, increasing model capacity beyond the interpolation threshold can improve generalization through double descent, but gains eventually encounter limits imposed by the data. The talk then considers scaling data and model size together, deriving compute-optimal relations for transformer-based jet taggers trained on as many as billions of simulated jets. It studies how training hyperparameters and input representations change these relations. The observed behaviour suggests that larger computing budgets could yield useful gains in particle physics, especially with a move toward more general-purpose foundation models.

Clarice D. Aiello examines evidence that quantum effects influence biological function, including magnetic sensing used in animal navigation, cellular metabolism and enzyme activity, and the capture of light energy in photosynthesis. The talk reviews proposed biophysical mechanisms and their implications for human, plant and environmental biology, while considering the difficulty of connecting observations from nanometre scales to whole organisms. A central question is whether quantum mechanics can be established or ruled out as the explanation for physiologically relevant effects, and whether those effects can be controlled for useful applications. Potential directions include biomimetic electromagnetic probes, quantum-computing architectures that operate at room temperature, improved solar-energy devices and new therapies. Progress will require work across disciplines and scales, with theory and experiment developed together.

This seminar investigates Anderson localization in subwavelength elastic periodic systems with random perturbations. For the unperturbed structure, layer-potential methods recast the eigenvalue problem as boundary integral equations, yielding asymptotic expressions for subwavelength eigenvalues and establishing a band gap above the subwavelength band. A Floquet transform then brings the perturbed problem into a periodic formulation and produces equations for resonant frequencies under general perturbations. Numerical experiments on monomer and dimer structures test agreement with the analysis. Increasing the strength and number of random perturbations demonstrates localization, providing a mathematical basis for elastic metamaterial design.

Ultrasound can levitate particles and create tunable interactions through sound scattered by nearby objects. In air, low viscosity permits underdamped collective dynamics far from equilibrium. Heinrich Jaeger discusses experiments that assemble small particles into freely suspended clusters and monolayer rafts while tracking their motion with high-speed video. Changing particle separation and acoustic energy transforms close-packed solids into soft lattices and unusual two-dimensional liquids. These experiments provide a platform for investigating non-reciprocal many-body forces and the collective behaviour they produce.

Tomas Sykora examines topological physics that perturbation theory cannot capture. Complex field configurations in path integrals include solitons, monopoles, domain walls, cosmic strings, sphalerons, baryon junctions and instantons; non-perturbative effects are central to confinement and hadron masses and spins. Starting with tunnelling in a double-well potential and imaginary time, the talk follows instantons into QCD, covering the theta vacuum, strong CP and axions, chiral symmetry breaking, topology and resurgence. It also considers whether a gluonic Y-shaped baryon junction carries baryon number instead of the valence quarks. The experimental discussion reviews instanton searches at HERA and the LHC, junction searches at RHIC, and prospective Electron-Ion Collider tests. No confirmed signal is claimed. Speaker: Tomas Sykora, Faculty of Mathematics and Physics, Charles University. Organized by Jiří Hejbal and Roman Lysák at FZU. Thursday 15 October 2026, 10:00–11:00 Europe/Prague (CEST). Attend at Dvořák Hall, FZU, Pod Vodárenskou věží 1, Prague, Czechia, or use the public Zoom link on the organizer’s event page.

Vladimir Zakharov presents the tangent-fermion approach to simulating a single chiral fermion on a lattice. Conventional local discretizations that preserve chirality generate unwanted copies of the Dirac cone. Tangent fermions retain one cone and ordinary on-site chiral symmetry by allowing nonlocal hopping. Other elements remain local: the generalized eigenvalue problem, a Euclidean action suitable for quantum Monte Carlo without a sign problem, and an exact matrix-product operator with fixed bond dimension for tensor-network calculations. Applications illustrate Luttinger-liquid behaviour, spontaneous symmetry breaking at a quantum spin Hall insulator’s edge, and symmetric mass generation in the 3-4-5-0 model.

This talk develops a first-principles description of interacting electrons, nuclei and electromagnetic fields by extending density-functional theory to quantum electrodynamics. It introduces electron–photon exchange-correlation functionals and photon many-body dispersion, a generalization of molecular dispersion methods that treats electronic and photonic degrees of freedom together. Applications examine anisotropic coupling, effects beyond single photons and cavity-modified van der Waals forces. The approach aims to retain these strong-coupling effects while remaining efficient enough to simulate large, complex systems inside optical cavities.

Petar Suman explores how higher-order statistics of the cosmic microwave background connect inflationary theory to observations. Although single-field inflation explains the origin of primordial fluctuations, its particle-physics mechanism remains uncertain. The first part examines the cosmological-collider programme: massive fields during inflation can leave oscillatory signatures in primordial non-Gaussianity, allowing measurements to constrain the masses and spins of early-universe particles. The second treats inflation as an open quantum system. An open effective field theory describes dissipation produced when the inflaton interacts with an environmental bath; joint analysis of the CMB power spectrum and bispectrum can then constrain those dynamics. Together, these approaches use precise cosmological data to test complex inflationary models at energies inaccessible to terrestrial accelerators.

Intermediate-band solar cells seek to absorb photons below the host band gap and increase current without sacrificing voltage. This talk examines submonolayer CdTe quantum dots embedded in ZnCdSe matched to InP, avoiding a harmful wetting layer and permitting hundreds of absorbing layers. Recent growth results show deeper photoluminescence associated with larger dots and improved intermediate-band placement. A complementary inverse-design study optimizes ZnCdSe/ZnCdMgSe distributed Bragg reflectors to recycle photons over 1–1.8 micrometres and incidence angles of 0–70 degrees. Total absorption guides optimization, with designs showing broad reflectivity and tolerance to fabrication errors.

The talk explores a quantitative connection between Huygens’s legacies in wave optics and classical mechanics. Optical polarization, coherence and entanglement are related to mechanical quantities including centre of mass and moment of inertia. Distributions of classical point masses provide a representation of nonseparability in optical fields, and the correspondence extends to quantum states of two qubits. These mappings offer an intuitive way to examine entanglement and the shared mathematical structure of mechanics, classical optics and quantum physics.

Gang Chen delivers MIT.nano's annual Dresselhaus Lecture, drawing on research that spans electron and phonon transport, thermoelectric energy conversion, microelectronic thermal management, desalination and data-center cooling.