# From 4d Yang-Mills to 2d $\mathbb{CP}^{N-1}$ model: IR problem and confinement at weak coupling

## TL;DR

This paper connects 4D SU(N) Yang-Mills theory to the 2D CP^{N-1} model via compactification, demonstrating preserved center symmetry at weak coupling and analyzing non-perturbative effects like fractional instantons and Borel plane singularities.

## Contribution

It establishes a detailed link between 4D Yang-Mills and 2D CP^{N-1} models, showing how twisted boundary conditions and fractional instantons restore center symmetry.

## Key findings

- Center symmetry remains unbroken at weak coupling.
- Fractional instantons connect multiple vacua.
- Borel plane singularities depend on compactification shape.

## Abstract

We study four-dimensional $\mathrm{SU}(N)$ Yang-Mills theory on $\mathbb{R} \times \mathbb{T}^3=\mathbb{R} \times S^1_A \times S^1_B \times S^1_C$, with a twisted boundary condition by a $\mathbb{Z}_N$ center symmetry imposed on $S^1_B \times S^1_C$. This setup has no IR zero modes and hence is free from IR divergences which could spoil trans-series expansion for physical observables. Moreover, we show that the center symmetry is preserved at weak coupling regime. This is shown by first reducing the theory on $\mathbb{T}^2=S_A \times S_B$, to connect the model to the two-dimensional $\mathbb{CP}^{N-1}$-model. Then, we prove that the twisted boundary condition by the center symmetry for the Yang-Mills is reduced to the twisted boundary condition by the $\mathbb{Z}_N$ global symmetry of $\mathbb{CP}^{N-1}$. There are $N$ classical vacua, and fractional instantons connecting those $N$ vacua dynamically restore the center symmetry. We also point out the presence of singularities on the Borel plane which depend on the shape of the compactification manifold, and comment on its implications.