Radiative capture on neutron rich nuclei

The $({\rm n},\gamma)$--cross sections for neutron--rich oxygen isotopes have been calculated in the direct capture model. The experimental data for ${^{18}{\rm O}}({\rm n},\gamma){^{19}{\rm O}}$ can be reproduced using this model. Compared to previous work the cross section for ${^{19-21}{\rm O}}({\rm n},\gamma){^{20-22}{\rm O}}$ are enhanced considerably by factors between four and 300.Comment: 5 pages + 1 figure (availbale on request), LaTex, IK-TUW-Preprint 940640

Fine-tuning the basic forces of nature through the triple-alpha process in red giant stars

We show that the synthesis of carbon and oxygen through the triple-alpha process in red giant stars is extremely sensitive to the fine details of the nucleon-nucleon (N-N) interaction. A +/-0.5% change in the strength of the N-N force would reduce either the carbon or oxygen abundance by as much as a factor of 30-1000. This result may be used to constrain some fundamental parameters of the Standard Model.Comment: 3 pages with 2 figures. Proceedings of the Nuclei in the Cosmos Conference, Aarhus, Denmark, June 27-July 1, 2000. To be published in Nuclear Physics A. The postscript file and more information are available at http://matrix.elte.hu/~csoto http://info.tuwien.ac.at/e142/ and http://www.MPA-Garching.MPG.DE/~schlattl

Stellar production rates of carbon and its abundance in the universe

The bulk of the carbon in our universe is produced in the triple-alpha process in helium-burning red giant stars. We calculated the change of the triple-alpha reaction rate in a microscopic 12-nucleon model of the C-12 nucleus and looked for the effects of minimal variations of the strengths of the underlying interactions. Stellar model calculations were performed with the alternative reaction rates. Here, we show that outside a narrow window of 0.5 and 4% of the values of the strong and Coulomb forces, respectively, the stellar production of carbon or oxygen is reduced by factors of 30 to 1000.Comment: 6 pages with 1 figure. Science, 2000 July 7 issue. The postscript file and more information are available at http://info.tuwien.ac.at/e142/, http://nova.elte.hu/~csoto and http://www.MPA-Garching.MPG.DE/~schlattl

Bridging the mass gaps at A=5 and A=8 in nucleosynthesis

In nucleosynthesis three possible paths are known to bridge the mass gaps at A=5 and A=8. The primary path producing the bulk of the carbon in our Universe proceeds via the triple-alpha process He4(2alpha,gamma)C12. This process takes place in helium-burning of red giant stars. We show that outside a narrow window of about 0.5% of the strength or range of the strong force, the stellar production of carbon or oxygen through the triple-alpha process is reduced by factors of 30 to 1000. Outside this small window the creation of carbon or oxygen and therefore also carbon-based life in the universe is strongly disfavored. The anthropically allowed strengths of the strong force also give severe constraints for the sum of the light quark masses as well as the Higgs vacuum expectation value and mass parameter at the 1% level