Unquenched QCD with Light Quarks

TL;DR

This paper introduces a novel lattice QCD simulation method using the truncated determinant approximation, enabling calculations at lighter quark masses and providing new insights into static energy, topological charge, and meson spectra.

Contribution

The paper presents the truncated determinant approximation (TDA) for unquenched lattice QCD, allowing simulations at lighter quark masses with improved efficiency and accuracy.

Findings

Successful simulation of static energy and topological charge distributions.

Preliminary results for meson spectrum at quark masses with pions ≤ 200 MeV.

Implementation of multiboson techniques to make TDA exact with minimal computational cost.

Abstract

We present recent results in unquenched lattice QCD with two degenerate light sea quarks using the truncated determinant approximation (TDA). In the TDA the infrared modes contributing to the quark determinant are computed exactly up to some cutoff in quark off-shellness (typically 2$\Lambda_{QCD}$). This approach allows simulations to be performed at much lighter quark masses than possible with conventional hybrid MonteCarlo techniques. Results for the static energy and topological charge distributions are presented using a large ensemble generated on very coarse (6$^4$) but physically large lattices. Preliminary results are also reported for the static energy and meson spectrum on 10$^3$x20 lattices (lattice scale $a^{-1}$=1.15 GeV) at quark masses corresponding to pions of mass $\leq$ 200 MeV. Using multiboson simulation to compute the ultraviolet part of the quark determinant the TDA approach becomes an exact with essentially no increase in computational effort. Some preliminary results using this fully unquenched algorithm are presented.