The present work reports results for (i) $\mathrm{pd}$ radiative capture observables at center-of-mass (c.m.) energies $<~2$ MeV; (ii) contributions to the Gerasimov-Drell-Hearn (GDH) integral of ${}^3\mathrm{He}$ in the threshold region; and (iii) longitudinal, transverse, and interference response functions, at excitation energies below the threshold for breakup into $ppn,$ of interest in ${}^3\mathrm{He}\to \left(\overrightarrow{e}{,e}^{\prime }\right)$ experiments. An exhaustive comparison of these results with available data from the TUNL and Wisconsin groups for $\mathrm{pd}$ capture, and from the Saskatoon group for threshold electrodisintegration of ${}^3\mathrm{He},$ is carried out. The calculations are based on pair-correlated-hyperspherical-harmonics bound and continuum wave functions obtained from a realistic Hamiltonian consisting of the Argonne $v_{18}$ two-nucleon and Urbana IX three-nucleon interactions. The electromagnetic current operator includes one- and two-body components, leading terms of which are constructed from the Argonne $v_{18}$ interaction. The theoretical predictions obtained by including only one-body currents are in violent disagreement with data. These differences between theory and experiment are, to a large extent, removed when two-body currents are taken into account, although some rather large discrepancies remain in the c.m. energy range 0–100 keV, particularly for the $\mathrm{pd}$ differential cross section $\sigma \left(\theta \right)$ and tensor analyzing power $T_{20}\left(\theta \right)$ at small angles, and contributions to the GDH integral. A rather detailed analysis indicates that these discrepancies have, in large part, a common origin, and can be traced back to an excess of $E_1$ strength obtained in the theoretical calculation as compared to that observed experimentally. It is suggested that this fact might have implications for the nuclear interaction at very low energies. Finally, the validity of the long-wavelength approximation for electric dipole transitions is discussed.

• Received 15 November 1999

DOI:https://doi.org/10.1103/PhysRevC.61.064001