# Degree 3 unramified cohomology of classifying spaces for exceptional groups

## TL;DR

This paper proves that the degree 3 unramified cohomology of classifying spaces for certain exceptional groups is trivial, completing the classification for all split semisimple groups of these types.

## Contribution

It establishes the triviality of degree 3 unramified cohomology for classifying spaces of exceptional groups, filling a gap in the classification of reductive invariants.

## Key findings

- Degree 3 unramified cohomology is trivial for these groups.
- Completes the classification for all split semisimple groups of these types.
- Supports previous results by Merkurjev and the author.

## Abstract

Let $G$ be a reductive group defined over an algebraically closed field of characteristic $0$ such that the Dynkin diagram of $G$ is the disjoint union of diagrams of types $G_{2}, F_{4}, E_{6}, E_{7}, E_{8}$. We show that the degree $3$ unramified cohomology of the classifying space of $G$ is trivial. In particular, combined with articles by Merkurjev \cite{Mer17} and the author \cite{Baek}, this completes the computations of degree $3$ unramified cohomology and reductive invariants for all split semisimple groups of a homogeneous Dynkin type.