Physics seminars

Explaining the cosmic matter–antimatter asymmetry requires baryogenesis before Big Bang nucleosynthesis. A precise treatment must evolve baryon and lepton flavour charges while including the relevant Standard Model Yukawa interactions and electroweak and QCD sphaleron processes. This talk introduces a full-flavour-covariant formalism and a new formalism covariant under quark flavour transformations. Applications include SO(10) leptogenesis and cloistered baryogenesis. The work also produces BOLEH, a public general-purpose code for BaryOn and Lepton charge Evolution in the Hot big bang.

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.

Scattering amplitudes constrain effective field theories from the bottom up through general consistency requirements, including unitarity and causality. Existing bounds mainly use four-point amplitudes. This talk explains how amplitudes with more external points supply additional constraints beyond the four-point analysis, and demonstrates the method through an application to Large-Nc quantum chromodynamics.

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.

Organic semiconductor molecules underpin the light-emitting diodes used in high-performance smartphone and television displays. Richard Friend traces the path from early discoveries to practical OLED technology and examines a wider range of applications, including solar cells, printable electronics and biological interfaces. He then discusses emerging phenomena in these materials and current work on their use as quantum sensors that can be accessed optically.

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.