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Dear all,</div>
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Please see below for details on this Friday's Topology Intercity Seminar. Regrettably, this clashes with DDT&G this time.</div>
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<b>From:</b> TopICS-l <topics-l-bounces@lists.science.uu.nl> on behalf of Subramanian, V. (Vignesh) via TopICS-l <topics-l@lists.science.uu.nl><br>
<b>Sent:</b> Friday, October 17, 2025 4:06 PM<br>
<b>To:</b> topics-l@lists.science.uu.nl <topics-l@lists.science.uu.nl><br>
<b>Subject:</b> [TopICS-l] TopICS on October 31, Nijmegen</div>
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<p style="margin: 0cm; font-family: Calibri, sans-serif; font-size: 11pt;"><span style="font-family: Aptos, sans-serif; font-size: 12pt;">Dear all,</span></p>
<p style="margin: 0cm; font-family: Calibri, sans-serif; font-size: 11pt;"><span style="font-family: Aptos, sans-serif; font-size: 12pt;">Hope you are doing well. Here are the details of the first TopICS meeting this semester in
<b>Nijmegen</b>.</span></p>
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<ul style="margin-bottom: 0cm;">
<li style="font-family: Calibri, sans-serif; font-size: 11pt; margin: 0cm;"><span role="presentation" style="font-family: Aptos, sans-serif; font-size: 12pt;"><b>Date</b>: Friday, October 31</span></li><li style="font-family: Calibri, sans-serif; font-size: 11pt; margin: 0cm;"><span role="presentation" style="font-family: Aptos, sans-serif; font-size: 12pt;"><b>Time</b>:
</span><span role="presentation" style="font-family: Aptos, sans-serif; font-size: 12pt; color: black;">13:30 to 17:30 </span></li><li style="font-family: Calibri, sans-serif; font-size: 11pt; margin: 0cm;"><span role="presentation" style="font-family: Aptos, sans-serif; font-size: 12pt;"><b>Place</b>:
</span><span role="presentation" style="font-family: Aptos, sans-serif; font-size: 12pt; color: black;">Nijmegen Huygensgebouw, Room: HG00.303</span></li></ul>
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<span role="presentation" style="font-family: Aptos, sans-serif; font-size: 12pt;"><b>Speakers and abstracts</b></span></li></ul>
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<span role="presentation" style="font-family: Aptos, sans-serif; font-size: 12pt;"><b>Steffen Sagave</b> (13:30 - 14:30)</span></li></ol>
<p style="margin: 0cm; font-family: Calibri, sans-serif; font-size: 11pt;"><span style="font-family: Aptos, sans-serif; font-size: 12pt; color: black;"><i><u>Title</u></i>: Logarithmic Topological Cyclic Homology</span></p>
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<p style="margin: 0cm; font-family: Calibri, sans-serif; font-size: 11pt;"><span style="font-family: Aptos, sans-serif; font-size: 12pt; color: black;"><i><u>Abstract</u></i>: Forming the fraction field of an integral domain is a classical construction in algebra.
The generalization of this notion to structured ring spectra is less obvious because inverting all non-zero homotopy classes often leads to a too drastic localization. For the connective complex topological K-theory spectrum and the connective Adams summand,
computations by Ausoni and Rognes suggest that a fraction field may be realized as a logarithmic ring spectrum with logarithmic structure generated by a given prime and the Bott element. In this talk, I will introduce logarithmic ring spectra, their topological
Hochschild homology, and their topological cyclic homology, and I will show how localization sequences for these theories help to identify a good candidate for a fraction field of topological K-theory spectra. </span></p>
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<p style="margin: 0cm; font-family: Calibri, sans-serif; font-size: 11pt;"><span style="font-family: Aptos, sans-serif; font-size: 12pt; color: black;">This is report on joint work in progress with John Rognes and Christian Schlichtkrull. </span></p>
<p style="margin: 0cm; font-family: Calibri, sans-serif; font-size: 11pt;"><span style="font-family: Aptos, sans-serif; font-size: 12pt;"> </span></p>
<p style="margin: 0cm; font-family: Calibri, sans-serif; font-size: 11pt;"><span style="font-family: Aptos, sans-serif; font-size: 12pt;"> 2.
<b>Luca Pol </b>(15:00-16:00)</span></p>
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<p style="margin: 0cm; font-family: Calibri, sans-serif; font-size: 11pt;"><span style="font-family: Aptos, sans-serif; font-size: 12pt; color: black;"><i><u>Title</u></i>: New Phenomena in the tt-geometry of global representations</span></p>
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<p style="margin: 0cm; font-family: Calibri, sans-serif; font-size: 11pt;"><span style="font-family: Aptos, sans-serif; font-size: 12pt; color: black;"><i><u>Abstract</u></i>: A global representation over a field is a compatible collection of representations
of the outer automorphism groups of the groups belonging to some collection of finite groups U. Global representations assemble into an abelian category AU which simultaneously generalizes classical representation theory and the category of VI-modules appearing
in the representation theory of the general linear groups. The derived category of global representations D(U) is an example of a non-rigid compactly generated tensor-triangulated category, which is known to be equivalent to the category of rational global
spectra for the family U. In this talk I would like to present some new phenomena that we encounter and explain some calculations of the Balmer spectrum in this setting. This is based on joint work with Miguel Barrero, Tobias Barthel, Neil Strickland and Jordan
Williamson.</span></p>
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<p style="margin: 0cm; font-family: Calibri, sans-serif; font-size: 11pt;"><span style="font-family: Aptos, sans-serif; font-size: 12pt; color: black;"> 3.
<b>Kathryn Hess</b> ( 16:30-17:30)</span></p>
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<p style="margin: 0cm; font-family: Calibri, sans-serif; font-size: 11pt;"><span style="font-family: Aptos, sans-serif; font-size: 12pt; color: black;"><i><u>Title</u></i>: From group actions to actegories.</span></p>
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<p style="margin: 0cm; font-family: Calibri, sans-serif; font-size: 11pt;"><span style="font-family: Aptos, sans-serif; font-size: 12pt; color: black;"><i><u>Abstract</u></i>: The notions of group action and of module over a ring can be categorified to that
of an actegory, consisting essentially of a functorial action of a monoidal category on a (2-)category. I will describe several interesting examples of actegories and of morphisms between them, in particular arising from group actions, and also explain how
to see (homotopy) colimits and limits as morphisms between two different actegory structures on the 2-category of categories. I’ll conclude by explaining how this type of actegory morphism can be used to build a machine that produces monads or comonads, like
those that are central to the construction of the discrete calculus of Bauer-Johnson-McCarthy.</span></p>
<p style="margin: 0cm; font-family: Calibri, sans-serif; font-size: 11pt;"><span style="font-family: Aptos, sans-serif; font-size: 12pt; color: black;"> </span></p>
<p style="margin: 0cm; font-family: Calibri, sans-serif; font-size: 11pt;"><span style="font-family: Aptos, sans-serif; font-size: 12pt; color: black;">Joint work with Kristine Bauer, Brenda Johnson, and Julie Rasmussen </span></p>
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<p style="margin: 0cm; font-family: Calibri, sans-serif; font-size: 11pt;"><span style="font-family: Aptos, sans-serif; font-size: 12pt; color: black;">Looking forward to meeting you in Nijmegen.</span></p>
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<p style="margin: 0cm; font-family: Calibri, sans-serif; font-size: 11pt;"><span style="font-family: Aptos, sans-serif; font-size: 12pt; color: black;">Best regards,</span></p>
<p style="margin: 0cm; font-family: Calibri, sans-serif; font-size: 11pt;"><span style="font-family: Aptos, sans-serif; font-size: 12pt; color: black;">Ahina and Vignesh </span></p>
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