Last updated: December 24, 2008

## Electromagnetic properties of hadrons

The goal of our project is compute hadron mass splittings due to the electromagnetic interaction using the first principles framework of lattice gauge theory. Thus the photons are treated in a similar fashion as the gluons in our combined simulation of QCD+QED. It is then straightforward to extract hadron masses, including effects of QED, from the exponential decay of two-point hadron correlation functions.

The goal for this year is to complete an initial study, using 2+1 flavor QCD lattices generated by the RBC and UKQCD collaborations, of the pseudoscalar mesons and the proton and neutron. These will allow explicit finite volume estimates of the QED effects (important for the nucleons) as well as determination of low energy constants to next-to-leading order in chiral perturbation theory for the mesons. In turn, one can determine the QED effects on the fundamental quark masses and separate the QED effects from those arising from unequal up and down quark masses on the mass splitting of the proton and neutron. The latter is expected to have the opposite sign to the QED effect, making the neutron heavier in Nature, a condition crucial to our very existence!

As of December 24, 2008, we have used 0% of our USQCD allocation on the QCDOC supercomputer at Brookhaven National Lab. We are ready to run, and will need 6 weeks on the 2K partion when it becomes available.

An earlier paper describing our method but using two flavor QCD can be found here.

Our recent results for 2+1 flavor QCD can be found here.

Our recent results for the proton-neutron mass splitting can be found here.