With the use of pionless effective field theory including dibaryon fields, we study the $gamma d to vec{n} p$ reaction for the laboratory photon energy $E_gamma^{lab}$ ranging from threshold to 30 MeV. Our main goal is to calculate the neutron polari
zation $P_{y}$ defined as $P_{y} = (sigma_+ - sigma_-)/(sigma_+ + sigma_-)$, where $sigma_+$ and $sigma_-$ are the differential cross sections for the spin-up and spin-down neutrons, respectively, along the axis perpendicular to the reaction plane. We also calculate the total cross section as well as the differential cross section $sigma(theta)$, where $theta$ is the colatitude angle. Although the results for the total and differential cross sections are found to agree reasonably well with the data, the results for $P_{y}$ show significant discrepancy with the experiment. We comment on this discrepancy.
The proton-proton fusion reaction, $ppto de^+ u$, is studied in pionless effective field theory (EFT) with di-baryon fields up to next-to leading order. With the aid of the di-baryon fields, the effective range corrections are naturally resummed up t
o the infinite order and thus the calculation is greatly simplified. Furthermore, the low-energy constant which appears in the axial-current-di-baryon-di-baryon contact vertex is fixed through the ratio of two- and one-body matrix elements which reproduces the tritium lifetime very precisely. As a result we can perform a parameter free calculation for the process. We compare our numerical result with those from the accurate potential model and previous pionless EFT calculations, and find a good agreement within the accuracy better than 1%.
