New lessons from the nucleon mass, lattice QCD and heavy baryon chiral perturbation theory

TL;DR

This paper reviews heavy baryon chiral perturbation theory and analyzes recent lattice QCD calculations of the nucleon mass, revealing both promising agreement and significant challenges in chiral extrapolations of baryon properties.

Contribution

It introduces a comprehensive analysis of lattice QCD results for the nucleon mass using chiral extrapolation methods, highlighting unexpected findings and the need for precise data.

Findings

Lattice results agree with the physical nucleon mass after extrapolation.

Linear fit functions in pion mass effectively describe lattice data.

High-precision data (1-2%) are necessary to resolve systematic uncertainties.

Abstract

I will review heavy baryon chiral perturbation theory for the nucleon delta degrees of freedom and then examine the recent dynamical lattice calculations of the nucleon mass from the BMW, ETM, JLQCD, LHP, MILC, NPLQCD, PACS-CS, QCDSF/UKQCD and RBC/UKQCD Collaborations. Performing the chiral extrapolations of these results, one finds remarkable agreement with the physical nucleon mass, from each lattice data set. However, a careful examination of the lattice data and the resulting extrapolation functions reveals some unexpected results, serving to highlight the significant challenges in performing chiral extrapolations of baryon quantities. All the N_f=2+1 dynamical results can be quantitatively described by theoretically unmotivated fit function linear in the pion mass with m_pi ~ 750 -190 MeV. When extrapolated to the physical point, the results are in striking agreement with the physical nucleon mass. I will argue that knowledge of each lattice datum of the nucleon mass is required at the 1-2% level, including all systematics, in order to conclusively determine if this is a bizarre conspiracy of lattice artifacts or rather a mysterious phenomenon of QCD.