An update on QCD+QED simulations with C* boundary conditions

TL;DR

This paper introduces new computational techniques for simulating dynamical QCD+QED with C* boundary conditions, including a faster algorithm for Pfaffian sign computation and a mass reweighting method, tested on ensembles with physical parameters.

Contribution

It presents a novel algorithm for Pfaffian sign determination and a reweighting approach for mass tuning in QCD+QED simulations with C* boundary conditions.

Findings

Significant speedup in Pfaffian sign computation.

Successful testing of techniques on ensembles with physical pion masses.

Validation of methods at different fine-structure constants.

Abstract

We present two novelties in our analysis of fully dynamical QCD+QED ensembles with C* boundary conditions. The first one is the explicit computation of the sign of the Pfaffian. We present an algorithm that provides a significant speedup compared to traditional methods. The second one is a reweighting of the mass in the context of the RHMC. We have tested the techniques on both pure QCD and QCD+QED ensembles with pions at $m_{\pi^\pm}\approx400$ MeV, a lattice spacing of $a\approx0.05$ fm, a fine-structure constant of $\alpha_{\mathrm{R}}=0$ and $0.04$.