Neutron electric polarizability

TL;DR

This study uses lattice QCD simulations with background fields to measure neutron and pion electric polarizabilities, observing their dependence on pion mass and comparing with theoretical predictions.

Contribution

It provides new lattice QCD results for neutron and pion electric polarizabilities at various pion masses, highlighting challenges and behaviors as quark mass decreases.

Findings

Neutron polarizability increases as pion mass drops below 500 MeV.

At the lowest pion mass, neutron polarizability is about one third of experimental value.

Pion polarizability becomes negative below 500 MeV, which is unexpected.

Abstract

We use the background field method to extract the "connected" piece of the neutron electric polarizability. We present results for quenched simulations using both clover and Wilson fermions and discuss our experience in extracting the mass shifts and the challenges we encountered when we lowered the quark mass. For the neutron we find that as the pion mass is lowered below $500\MeV$, the polarizability starts rising in agreement with predictions from chiral perturbation theory. For our lowest pion mass, $m_\pi=320\MeV$, we find that $\alpha_n = 3.8(1.3)\times 10^{-4}\fm^3$, which is still only one third of the experimental value. We also present results for the neutral pion; we find that its polarizability turns negative for pion masses smaller than $500\MeV$ which is puzzling.