|
Calendar of Physics Talks Vienna
| Surface observables in 4D BF and Yang Mills theories |
| Speaker: | Alberto Cattaneo (University of Zurich) |
| Abstract: | Abelian YangâMills theory possesses an interesting gauge-invariant observable defined as (the exponential of) the Hodge dual of the curvature integrated on a surface Sigma (this can be interpreted as the magnetic flux through Sigma). As emphasized by ât Hooft, a nonabelian version would be of significant interest. In this talk, I will first show how to obtain a surface observable for BF theory with cosmological constant. This is a topological field theory, and an AKSZ model, whose fields are a connection and a 2-form B, with equations of motions simply stating that B is proportional, by the âcosmological constant,âto the curvature. This is a nontrivial task which can be achieved through the BV formalism defining a second field theory on Sigma coupled to the ambient fields of BF theory. (As the previously known version for zero cosmological constant, the expectation value of this observab |
| Date: | Tue, 28.04.2026 |
| Time: | 14:00 |
| Duration: | 60 min |
| Location: | Erwin-Schroedinger-HS, Boltzmanngasse 5, 1090 Wien, 5.Stock |
| Contact: | S. Fredenhagen, M. Sperling |
| Exploring nanomagnetism within the transmission electron microscope |
| Speaker: | Daniel Wolf (Institute for Solid State Research, Leibniz Institute for Solid State and Materials Research Dresden, Dresden, Germany) |
| Abstract: | We use transmission electron microscopy (TEM)–based magnetic imaging to investigate magnetic nanostructures in two and three dimensions. [1] The method exploits the fundamental Aharonov–Bohm phase shift that arises when the transmitting electron wave interacts with both the specimen’s electrostatic potential and its magnetic vector potential. This magnetic phase shift can be employed in Lorentz TEM and off‑axis electron holography to map domain configurations (e.g., versus applied field), magnetic textures such as skyrmion lattices, and exotic domain walls like Bloch‑point walls in nanowires. In my talk, I will introduce the fundamentals of magnetic imaging, review the available methods, and address the challenges of acquiring and reconstructing three‑dimensional datasets with nanometer resolution. [2] Finally, I will showcase examples that illustrate how magnetic imaging can visualize S |
| Date: | Tue, 28.04.2026 |
| Time: | 16:00 |
| Location: | TU Wien, Institut für Angewandte Physik, E134 1040 Wien, Wiedner Hauptstraße 8-10 Yellow Tower „B“, 5th floor, SEM.R. DB gelb 05 B |
| Contact: | Prof. Dr.Amalio Fernandez-Pacheco |
| Coherence violation in jet observables |
| Speaker: | Andrea BANFI (University of Sussex) |
| Abstract: | In high-energy hadronic collisions, such as those occurring at the Large Hadron Collider, it is widely believed that radiation collinear to the two incoming protons can be absorbed into universal parton distribution functions, encoding the probability to extract a parton (quark or gluon) from a given hadron. This picture is based on a property of soft radiation known as coherence. However, Coulomb gluon exchanges between the incoming partons challenge coherence, and give rise to large logarithmic contributions to jet observables, whose general structure is elusive. These coherence violating effects were found for the first time in non-global observables such as the interjet energy flow.
In this talk, based on 2511.11799, I will show that they are also present in global observables, such as one-jettiness, giving rise to super-super-leading logarithms. |
| Date: | Tue, 28.04.2026 |
| Time: | 16:15 |
| Duration: | 60 min |
| Location: | Erwin-Schroedinger Lecture Hall, 1090 Vienna, Boltzmanngasse 5, 5th floor |
| Contact: | A. Hoang, J. Pradler, M. Procura |
| Self-induced Superradiant Masing |
| Speaker: | Oliver Diekmann (Institute for Theoretical Physics, TU Wien) |
| Abstract: | Dipole-dipole interactions between adjacent nitrogen vacancy centers in a diamond crystal are generally viewed as a source of decoherence. In our recent study [Kersten et al, Nat. Phys. 22, 158â163] we could draw a different picture for an ensemble of such emitters in a single mode cavity. Subsequently to well-understood spin-cavity dynamics, we find that the spin-spin interactions may reshuffle the energy within the inhomogeneously broadened ensemble. The redistribution of energy leads to the emission of an unexpected pulse train followed by a regime of superradiant masing only driven by energy transport within the ensemble. I will put a particular emphasis on discussing the theoretical models to reveal the nature of this energy transport and link it directly to magnetic dipole-dipole interactions. |
| Date: | Wed, 29.04.2026 |
| Time: | 16:15 |
| Duration: | 45 min |
| Location: | Atominstitut, Helmut Rauch Hörsaal, |
| Contact: | Elena Redchenko |
|