Kang, Ho-Shik | Engineering Papers

NASA NTRS1991

Primordial nucleosynthesis redux

The abundances of D, He-3, He-4, and Li-7, are presently recalculated within the framework of primordial nucleosynthesis in the standard hot big band model, in order to estimate the primordial abundances of the light elements. A comparison between theory and experiment demonstrates the consistency of standard model predictions; the baryon density parameter is constrained on the basis of a nucleon-to-photon ratio of 2.8-4.0. These bounds imply that the bulk of the baryons in the universe are dark, requiring that the universe be dominated by nonbaryonic matter.

Walker, Terry P.↗

NASA NTRS1988

Axions, SN 1987A, and one pion exchange

Nucleon-nucleon, axion bremsstrahlung is the primary mechanism for axion emission from the nascent neutron star associated with SN 1987A, and the rate for this process has been calculated in the one pion exchange approximation (OPE). The axion mass limit which follows from SN 1987A, m sub a less than or approx equal to 10 to the -3 eV, is the most stringent astrophysical bound, and has received much scrutiny. It has been suggested that by using OPE to calculate the cross section for the analog process, pp yields pp + pi sup o, and comparing the result of the experimental data one can test the validity of this approximation, and further, that such a comparison indicates that OPE leads to a value for this cross section which is a factor of 30 to 40 too large. If true, this would suggest that the axion mass limit should be revised upward by a factor of approximately 6. The cross section for pp yields pp + pi sup o using OPE is carefully evaluated, and excellent agreement found (to better than a factor of 2) with the experimental data.

Turner, Michael S.↗