# Hybrid Monte Carlo and topological modes of full QCD

## TL;DR

This paper examines the limitations of the hybrid Monte Carlo algorithm in updating topological structures in lattice QCD, revealing significant issues with decorrelating topological charge at current simulation parameters.

## Contribution

It highlights the challenges of using hybrid Monte Carlo for full QCD simulations, especially in handling topological modes, and warns of potential inaccuracies.

## Key findings

- Hybrid Monte Carlo struggles to decorrelate topological charge.
- Problems are significant at current simulation parameters.
- Results impact the reliability of full QCD simulations.

## Abstract

We investigate the performance of the hybrid Monte Carlo algorithm, the standard algorithm used for lattice QCD simulations involving fermions, in updating non-trivial global topological structures. We find that the hybrid Monte Carlo algorithm has serious problems decorrelating the global topological charge at the values of $\beta$ and $m$ currently simulated, where continuum physics should be approximately realized. This represents a warning which must be seriously considered when simulating full QCD by hybrid Monte Carlo.