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Time: 26. April 2024, 11:00h
Place: Institute of Physics, room 360
Speaker: Benedek Bukor
Title: What about quarkonia in the (non)commutative space?
Abstract:
Quarkonium bound states are especially promising candidates to test the probable quantum structure of space-time since they represent a system with a reasonably small characteristic distance. Although the theory of quarkonia is quantum chromodynamics, the interaction between the quarks can be heuristically described by the quantum mechanical Cornell potential as well. Firstly, we investigate the quarkonium system in the 3-dimensional smooth configuration space. Thereafter, we insert it into a non-commutative 3-dimensional configuration space, which is composed of concentric fuzzy spheres of increasing radius, called the fuzzy onion, in order to extract some consequences of the non-trivial structure of the space by means of the quarks' properties.
Time: 12. April 2024, 11:00h
Place: Institute of Physics, room 360
Speaker: Guillaume Trojani
Title: Perturbiner expansion: old and new
Abstract:
In their seminal, Berends and Giele identified an efficient algorithm for computing n-point tree level scattering amplitudes in gauge theory. Later, the pertubiner expansion was developed to generate the Berends-Giele recursion relation to study any quantum field theory at tree level. This talk aims to reintroduce these techniques in the light of the modern language of homotopy algebras, with an eye towards the recent development of loop level techniques. Indeed, the recursion relations are natural consequences of the Homotopy perturbation lemma relating an interacting field theory and its underlying free theory. Time permitting, I will comment on current work where we apply this algebraic machinery to braided field theories, which are noncommutative field theories deformed in a controlled manner.
Time: 29. March 2024, 11:00h
Place: Institute of Physics, room 360
Speaker: Petar Petrasinovic
Title: 2-groups and crossed modules: Classification and algorithm for constructing non-trivial ones
Abstract:
The 2-groups are category theory generalisations of the usual groups. They are equivalent to crossed modules, consisting of two groups, G and H, the homomorphism ∂ from H to G and the action ▷ from G to H. One can construct a gauge theory of gravity on a 4-manifold based on crossed modules (like the BFCG theory for the Poincaré 2-group). Besides the usual group axioms, crossed modules must satisfy additional axioms. For this reason, they are much more rigid structures and more difficult to construct. There are some typical examples, but they are very rare and in which either ∂ or ▷ is trivial. In this seminar, I will discuss the properties of their linear structure-differential crossed modules. A possible way to classify these modules will be shown. Together with the classification, a corresponding algorithm for constructing differential cross modules with non-trivial ∂ and ▷ will be presented, which constructs them either for given groups G and H or for given ∂ and ▷.
Time: 15. March 2024, 11:00h
Place: Institute of Physics, room 360
Speaker: Petar Petrasinovic
Title: Moore-Penrose inverse of matrix and its application to solving general linear systems
Abstract:
In linear algebra, the Moore-Penrose inverse stands as a generalization of the conventional matrix inverse, having been independently introduced by E.H. Moore in 1920 and later by Roger Penrose in 1955. The Moore-Penrose inverse is uniquely defined for all matrices whose entries are either real or complex numbers and extends its applicability to rectangular and even singular matrices. The versatility and uniqueness of the Moore-Penrose inverse are the major reasons for its significance (and discovery), which is reflected in solving general linear systems of equations, or tensor systems which can be reshaped into matrix form. In this seminar, I will discuss the properties of the Moore-Penrose inverse, display some of the calculation methods, and demonstrate its practical applications.
Time: 23. February 2024, 11:00h
Place: Institute of Physics, room 360
Speaker: Mihailo Cubrovic
Title: Chaos and factorization beyond classical horizons
Abstract:
Chaotic dynamics of black holes has proven to be of vital importance for the understanding of the black hole information problem. Within the replica formalism, a related issue is that of nonfactorization of partition functions of wormhole geometries. We consider these questions deep in the stringy regime, described by the BFSS and IKKT matrix models, where the notions of geometry and horizon do not apply anymore. Generic solutions factorize when averaged over the quantum fluctuations, whereas the chaotic properties are non-universal. We argue that the correct notion that characterizes the black hole scrambling is instead that of quantum magic (stabilizer Renyi entropy), which guarantees that the dynamics is complex enough to accommodate the total information on infalling matter.
Time: 2. February 2024, 11:00h
Place: Institute of Physics, room 360
Speaker: Dusan Djordjevic
Title: Massless minimally coupled scalar field in dS spacetime
Abstract:
In this talk, we will review the quantisation of scalar fields in de-Sitter spacetime. We will discuss the differences between the case of minimally coupled massive and minimally coupled massless scalar fields, as well as the possibility of obtaining, in the massless case, a vacuum state that is invariant under the full SO(4,1) group. The talk will be based on the following papers:
Klaus Kirsten, Jaume Garriga, arXiv:gr-qc/9305013
Andrew Tolley, Neil Turok, arXiv:hep-th/0108119
Seminars for the year:
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