Impact of Dynamical Fermions on QCD Vacuum Structure

Abstract

We examine how dynamical fermions affect both the UV and infrared structure of the QCD vacuum. We consider large $28^3\times 96$ lattices from the MILC collaboration, using a gluonic definition of the topological charge density, founded on a new over-improved stout-link smearing algorithm. The algorithm reproduces established results from the overlap formalism and is designed to preserve nontrivial topological objects including instantons. At short distances we focus on the topological charge correlator, $<q(x)q(0)>$, where negative values at small $x$ reveal a sign-alternating layered structure to the topological-charge density of the QCD vacuum. We find that the magnitudes of the negative dip in the $<q(x)q(0)>$ correlator and the positive $<q(0{)}^2>$ contact term are both increased with the introduction of dynamical fermion degrees of freedom. This is in accord with expectations based on charge renormalization and the vanishing of the topological susceptibility in the chiral limit. At large distances we examine the extent to which instanton-like objects are found on the lattice, and how their distributions vary between quenched and dynamical gauge fields. We show that dynamical gauge fields contain more instanton-like objects with an average size greater than in the quenched vacuum. Finally, we directly visualize the topological charge density in order to investigate the effects of dynamical sea-quark degrees of freedom on topology.

9 pages, 8 figures

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Cited by in corpus (14)

• 50 Years of Quantum Chromodynamics
• Glueball spectrum from $N_f=2$ lattice QCD study on anisotropic lattices
• Connection between centre vortices and instantons through gauge-field smoothing
• Topology of dynamical lattice configurations including results from dynamical overlap fermions
• Correlation and localization properties of topological charge density and the pseudoscalar glueball mass in SU(3) lattice Yang-Mills theory
• Wilson mass dependence of the overlap topological charge density
• Quark Propagation in the Instantons of Lattice QCD
• Instanton contributions to the low-lying hadron mass spectrum
• Smoothing algorithms for projected center-vortex gauge fields
• Filtered topological structure of the QCD vacuum: Effects of dynamical quarks
• Instanton dominance over ${\alpha }_s$ at low momenta from lattice QCD simulations at $N_f=0$, $N_f=2+1$ and $N_f=2+1+1$
• Comparison of filtering methods in SU(3) lattice gauge theory
• Comparing the vacuum structure of quenched and dynamical configurations
• Role of the Wilson mass parameter in the overlap Dirac topological charge density