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Shauly Ragimov (U Chicago): Universality of character theory

Event Type
Seminar/Symposium
Sponsor
UIUC Math Department
Location
Altgeld 243
Date
Oct 28, 2025   11:00 am  
Views
60
Originating Calendar
Topology Seminar
A key tool in the computation of En-cohomology of π-finite spaces is the transchromatic character, constructed by Hopkins-Kuhn-Ravenel and extended by Stapleton and Lurie. For each 0 ≤ (n − t) ≤ n, the height (n − t)-transchromatic character relates the En-cohomology of a π-finite space to that of its (n − t)-fold p-typical loop space, evaluated with respect to a height t-cohomology theory.
                   

We place this construction into a unified framework of (n − t)-fold character theories ap- plicable to any ∞-commutative monoid. Concretely, for an ∞-commutative monoid R there is a universal (n − t)-fold character map that respects the natural induction and restriction structures of R. In particular, it yields a character theory for every T(n)-local algebra. This universal character enjoys strong structural properties: it exhibits a blue-shift phenomenon by sending T(n)-local algebras to T(t)-local algebras, and it carries primitive height-n roots of unity to primitive height-t roots of unity. In the case of En, it recovers the classical transchro- matic character.

                
            
        

   

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