Nucleon-pion state contamination in lattice calculations of nucleon observables

April 6, 2017
3:00pm to 4:30pm

IFT Seminar Room/Red Room

Specialist level
Speaker: 
Oliver Bär
Institution: 
Humboldt University Berlin
Location&Place: 

IFT Seminar Room/Red Room

Abstract: 
Excited-state contaminations in Lattice QCD calculations are expected to become rapidly severe for small quark masses. The calculation of nucleon observables is a familiar example where multi-particle states with additional pions are expected to become a significant excited-state contamination. The multi-particle states expected to be most relevant in this case are two-particle nucleon-pion states. We show how ChPT can be employed to calculate these nucleon-pion-state contaminations and present leading order results for the axial, tensor and scalar charge of the nucleon and various moments of parton distribution functions. Estimates are given for lattice simulations with a physical pion mass. In this case the nucleon-pion contribution is found to be at the 5-20% level, and rather large source-sink separations are required to reduce them significantly.