# RTG Seminar Winter 2024/25

## RTG Seminar Winter term 2024

The Thursday morning seminar (10:15-11:45 in **WSC-N-U-3.05**) will be the “Research Training Group Seminar” where members of the RTG (PhD students, post-docs,…) present their results. Sometimes, we also have speakers from other places. Depending on the number of speakers and on the proposed topic, a speaker could use one or two sessions.

31.10.2024 | Carolina Tamborini | Non-tautological double cover cycles |

7.11.2024 | Andreas Pieper | Newton meets Torelli |

14.11.2024 | Sebastian Bartling | Some remarks on Brauer groups of proper and smooth Deligne-Mumford stacks over the integers. |

21.11.2024 | Pietro Gigli | tba |

28.11.2024 | reserved | general assembly |

5.12.2024 | Robert Franz | tba |

12.12.2024 | N. N. | tba |

19.12.2024 | N. N. | tba |

9.1.2025 | Thiago Solovera y Nery | tba |

16.1.2025 | Maximilian Hauck | Syntomic cohomology and stacks in p-adic geometry |

23.1.2025 | Lukas Bröring | tba |

30.1.2025 | N. N. | tba |

## Abstracts

### Carolina Tamborini: Non-tautological double cover cycles.

After an introduction on moduli spaces of curves and their tautological rings, I will discuss joint works together with V. Arena, S. Canning, E. Clader, R. Haburcak, A.Q. Li, and S.C. Mok and with D. Faro on the construction of many new non-tautological algebraic cohomology classes arising from double cover cycles, generalising previous work by Graber-Pandharipande and van Zelm.

### Andreas Pieper: Newton meets Torelli.

The Newton stratification is a natural refinement of the $f$-number stratification of the moduli space $\mathcal{A}_g$ in characteristic $p>0$. In the beginning of the talk I will define the stratification and discuss its properties. The main part will be about the restriction of the Newton-stratification to the Torelli locus. Here much less is known; despite numerous contributions there is no complete (even conjectural) picture of questions regarding non-emptiness, dimensions, or the closure relation.

I will report on work in progress that shows that all the Newton strata on $\mathcal{M}_4$ are not empty and have the expected dimension.