##### Department of Mathematics,

University of California San Diego

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### Group Actions Seminar

## Felix Weilacher - Graduate student

#### Carnegie Mellon University

## Marked groups with isomorphic Cayley graphs but different Descriptive combinatorics

##### Abstract:

We discuss the relationship between the Borel measurable / Baire measurable combinatorics of the action of a finitely generated group on its Bernoulli shift and the discrete combinatorics of the multiplication action of that group on itself. Our focus is on various chromatic numbers of graphs generated by these actions. We show that marked groups with isomorphic Cayley graphs can have Borel measurable / Baire measurable chromatic numbers which differ by arbitrarily much. In the Borel two-ended, Baire measurable, and measurable hyperfinite settings, we show our constructions are nearly best possible (up to only a single additional color), and we discuss prospects for improving our constructions in the general Borel setting. Along the way, we will get tightness of some bounds of Conley and Miller on Baire measurable and measurable chromatic numbers of locally finite Borel graphs.

Host: Brandon Seward

### January 19, 2021

### 9:00 AM

### Zoom ID 967 4109 3409 (email Nattalie Tamam or Brandon Seward for the password)

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