62 research outputs found
Nuclear physics input for solar models
We discuss microscopic cluster model descriptions of two solar nuclear
reactions, Be7(p,gamma)B8 and He3(He3,2p)He4. The low-energy reaction cross
section of Be7(p,gamma)B8, which determines the high-energy solar neutrino
flux, is constrained by Be7 and B8 observables. Our results show that a small
value of the zero-energy cross section is rather unlikely. In He3(He3,2p)He4 we
study the effects of a possible virtual state on the cross section. Although,
we have found no indication for such a state so far, its existence cannot be
ruled out yet. We calculate the He3(He3,2p)He4 and H3(H3,2n)He4 cross sections
in a continuum-discretized coupled channel approximation, and find a good
general agreement with the data.Comment: 9 pages with 4 figures. Invited talk given at the "XVII RCNP
International Symposium on Innovative Computational Methods in Nuclear
Many-Body Problems" (November 10-15, 1997, Osaka, Japan). To appear in the
conference proceedings. The postscript file with color figures and more
information are available at http://qmc.lanl.gov/~csot
Microscopic calculations for solar nuclear reactions
We have studied the 4He(3He,gamma)7Be, 3He(3He,2p)4He, and 7Be(p,gamma)8B
reactions of the solar p-p chain, using microscopic cluster models. Among other
results, we showed that the 6Li+p channel has a nontrivial effect on the
7Be-producing reaction, that the existence of a resonance in 6Be close to the
3He+3He threshold is rather unlikely, and that the correlations between some
properties of 7Be/8B and the low-energy cross section of 7Be(p,gamma)8B might
help one to constrain the value of the S_17(0) astrophysical S-factor.Comment: 3 pages with 1 figure. 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 and http://www.dfi.aau.dk/~langanke
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
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