Vladimir Pascalutsa

Chiral perturbation theory of muonic hydrogen Lamb shift: polarizability contribution

The proton polarizability effect in the muonic-hydrogen Lamb shift comes out as a prediction of baryon chiral perturbation theory at leading order and our calculation yields

Quark transverse charge densities in the Delta(1232) from lattice QCD

\Delta E^{(\mathrm{pol})} (2P-2S) = 8^{+3}_{-1}\, \upmu

Sum rules for light-by-light scattering.

ΔE(pol)(2P-2S)=8-1+3μeV. This result is consistent with most of evaluations based on dispersive sum rules, but it is about a factor of 2 smaller than the recent result obtained in heavy-baryon chiral perturbation theory. We also find that the effect of

\Delta

\Delta (1232)

Magnetic Moments of Delta and Omega- baryons with dynamical clover fermions

Δ(1232)-resonance excitation on the Lamb shift is suppressed, as is the entire contribution of the magnetic polarizability; the electric polarizability dominates. Our results reaffirm the point of view that the proton structure effects, beyond the charge radius, are too small to resolve the ‘proton radius puzzle’.

Large-N(c) relations for the electromagnetic N to Delta(1232) transition

We develop techniques to calculate the four