# Arithmetic Chern-Simons theory with real places

## TL;DR

This paper extends arithmetic Chern-Simons theory to include number fields with real places and constructs new non-trivial invariants with non-abelian gauge groups, broadening the scope of previous models.

## Contribution

It generalizes arithmetic Chern-Simons theory to arbitrary number fields with real places and provides new non-trivial examples with non-abelian gauge groups and general coefficients.

## Key findings

- Extended theory to include real places using cohomology with compact support.
- Constructed new non-trivial invariants with non-abelian gauge groups.
- Provided explicit examples via a twisting argument.

## Abstract

The goal of this paper is two-fold: we generalize the arithmetic Chern-Simons theory over totally imaginary number fields studied in [Kim15, CKK+16] to arbitrary number fields (with real places) and provide new examples of non-trivial arithmetic Chern-Simons invariant with coefficient $\mathbb{Z}/n\mathbb{Z}$ $(n \geq 2)$ associated to a non-abelian gauge group. The main idea for the generalization is to use cohomology with compact support (see [Mil06]) to deal with real places. Before the results of this paper, non-trivial examples were limited to some non-abelian gauge group with coefficient $\mathbb{Z}/2\mathbb{Z}$ in [CKK+16] and the abelian cyclic gauge group with coefficient $\mathbb{Z}/n\mathbb{Z}$ in [BCG+18]. Our non-trivial examples (with non-abelian gauge group and general coefficient $\mathbb{Z}/n\mathbb{Z}$) will be given by a simple twisting argument based on examples of [BCG+18].