Richard N. Fell

Order alpha(2) corrections to the decay rate of orthopositronium

Order alpha(2) corrections to the decay rate of orthopositronium are calculated in the framework of nonrelativistic QED. The resulting contribution is found to be in significant disagreement with one set of experimental measurements, though another experiment is in agreement with theory.

Positronium hyperfine splitting at order

We have calculated the contribution to the positronium hyperfine splitting at order

m \alpha^7

m \alpha^7

: light-by-light scattering in the two-photon-exchange channel

of the light-by-light scattering process in the exchange of two photons between the electron and positron. Our result is

Positronium energy levels at ordermα7: Light-by-light scattering in the two-photon-annihilation channel

\Delta E = -0.235355(8) m \alpha^4 \left ( \frac{\alpha}{\pi} \right )^3 = -1.034 kHz

Two-loop corrections to the decay rate of parapositronium

. As a check of our approach we confirm earlier evaluations of the analogous correction for a bound system (such as muonium) with unequal masses.

Two-Loop Corrections to the Decay Rate of Orthopositronium

Recent and ongoing experimental work on the positronium spectrum motivates new efforts to calculate positronium energy levels at the level of three loop corrections. We have obtained results for one set of such corrections involving light-by-light scattering of the photons produced in a two-photon virtual annihilation process. Our result is an energy shift

Cosmological perturbations on local systems

1.58377(8) m \alpha^7/\pi^3

Order alpha 4 ln alpha -1 fRYD corrections to the n=1 and n=2 energy levels of positronium.

for the n=1 singlet state, correcting the ground state hyperfine splitting by -6.95 kHz. We also obtained a new and more precise result for the light-by-light scattering correction to the real decay of parapositronium into two photons.

Two-Loop Correction to the Orthopositronium Decay Rate

Order-{alpha}{sup 2} corrections to the decay rate of parapositronium are calculated. A QED scattering calculation of the amplitude for electron-positron annihilation into two photons at threshold is combined with the technique of effective field theory to determine a nonrelativistic QED Hamiltonian, which is then used in a bound-state calculation to determine the decay rate. Our result for the two-loop correction is 5.124 3(33) in units of ({alpha}/{pi}){sup 2} times the lowest-order rate. This is consistent with but more precise than the result 5.1(3) of a previous calculation.