Date | Title | Speaker | Abstract |
---|---|---|---|

02.03.2021 | Machine learning and SU(3) structures on six manifolds | James Gray | In this talk we will discuss the application of Machine Learning techniques to obtain numerical approximations to various metrics of SU(3) structure on Calabi-Yau manifolds. More precisely, we will be interested in SU(3) structures whose torsion classes make them suitable backgrounds for various string compactifications. A variety of aspects of this topic will be covered. These will include learning moduli dependent Ricci-Flat metrics on Calabi-Yau threefolds and obtaining numerical approximations to torsional SU(3) structures. |

09.03.2021 | Anomalous field theories as boundaries | Lukas Müller | This talk will be about the description of anomalies in quantum field theory through boundary states of certain field theories in one dimensions higher. I will give a gentle introduction to the mathematical formulation of this approach developed by Freed and Monnier and explain its relation to more classical approaches. I will discuss two concrete examples in detail, namely the parity anomaly of fermionic gauge theories in odd spacetime dimensions and 't Hooft anomalies of discrete gauge theories. Time permitting I will mention some open questions related to smooth families of field theories. The talk is based on joint work with R. J. Szabo. |

16.03.2021 | Asymptotic charges in gravity | Mahdi Godazgar | I will discuss the Hamiltonian derivation of dual BMS charges at null infinity using the first order formalism. More generally, I will discuss how this idea can be used to classify asymptotic charges in gravity. |

23.03.2021 | Perturbative Quantization of Einstein-Hilbert Gravity | Klaus Sibold | In a perturbative approach Einstein-Hilbert gravity is quantized about a flat background. In order to render the model power counting renormalizable, higher order curvature terms are added to the action. They serve as Pauli-Villars type regulators and require an expansion in the number of fields in addition to the standard expansion in the number of loops. Renormalization is then performed within the BPHZL scheme, which provides the action principle to construct the Slavnov-Taylor identity and invariant differential operators. After removal of the regulators, the final physical state space of the Einstein-Hilbert theory is realized via the quartet mechanism of Kugo and Ojima. Renormalization group and Callan-Symanzik equation are derived for the Green functions and, formally, also for the S-matrix. |

30.03.2021 | Easter break | - | |

06.04.2021 | Easter break | - | |

13.04.2021 | O(D,D) and string alpha'-corrections | Linus Wulff | String theory on a d-dimensional torus features an O(d,d) duality symmetry. It has been suggested that the low-energy effective action can be formulated with a larger O(D,D) symmetry (D=10 or 26), even before putting the theory on a torus. This approach, which goes by the name of Double Field Theory (DFT), has proven very useful. I will address the problem of constructing higher derivative invariants in this formalism. In agreement with the literature we find that a quadratic Riemann invariant can be constructed, which can account for the first alpha'-correction to the bosonic and heterotic string. However, we find that no cubic or quartic Riemann invariants can be constructed. This suggests that the quartic Riemann terms arising at order alpha'^3 in string theory do not have a DFT embedding. |

20.04.2021 | Resurgence and BPS invariants | Jie Gu | Asymptotic series abound in physics. Borel resummation and resurgence theory are among the powerful tools to deal with them. The former provides a way to convert asymptotic series to numbers, the latter reveals that different asymptotic series at different saddle points are related to each other by Stokes automorphism characterised by Stokes constants. We argue that the Stokes constants can be treated as new invariants of the system, and in many cases can be interpreted as counting BPS states. We support this statement with examples in Seiberg-Witten theory, complex Chern-Simons theory, and topological string theory. |

27.04.2021 | Digging traversable wormholes | Roberto Emparan | In recent years there have appeared several constructions of traversable wormholes, in four and other dimensions, which only involve physically acceptable, controllable ingredients. They connect in deep ways many aspects of gravity, quantum field theory, and quantum information. I will discuss several features of these constructions, with a focus on traversability, connectivity between multiple mouths, and the (im)possibility of time travel. |

04.05.2021 | CFTs and Wightman axioms in general dimensions | Petr Kravchuk | In Conformal Field Theory, one is often concerned with computing local correlation functions from the spectrum of local operators and their OPE coefficients. In general quantum field theories, we expect these correlation functions to satisfy Wightman and Osterwalder-Schrader axioms. In this talk, I will explain that Wightman axioms are not obvious for CFT correlation functions and then present a proof for correlators up to four points. In the process I will also briefly review the classic results relating Wightman and O-S axioms, which have caveats that are important in the CFT setup. |

11.05.2021 | t.b.a. | t.b.a. | t.b.a. |

18.05.2021 | t.b.a. | Johannes Thürigen | t.b.a. |

25.05.2021 | t.b.a. | Claudia de Rham | t.b.a. |

01.06.2021 | t.b.a. | t.b.a. | t.b.a. |

08.06.2021 | t.b.a. | t.b.a. | t.b.a. |

15.06.2021 | t.b.a. | Jun Nishimura | t.b.a. |

22.06.2021 | No talk due to Strings 2021 | t.b.a. | t.b.a. |

29.06.2021 | t.b.a. | t.b.a. | t.b.a. |

The Joint Theory Seminar is currently held online via BigBlueButton.

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Black holes and holography

Technische Universität Wien

Mathematical physics

University of Vienna

Black holes and holography

Technische Universität Wien

Mathematical physics

University of Vienna