The 12 C+ 12 C fusion cross sections show resonant behavior down to the lowest energies accessible so far in the laboratory. If this tendency continues into the astrophysical energy range, the stellar 12 C+ 12 C reaction rates have to be corrected for resonant screening effects, in addition to the conventional screening corrections. We estimate the resonant screening effects in the weak electron screening limit for hydrostatic burning and white dwarf environments.

The electron-screening acceleration of laboratory fusion reactions at astrophysical energies is an unsolved problem of great importance to astrophysics. That effect is modeled here by considering the fusion of hydrogen-like atoms whose electron probability density is used in Poisson's equation in order to derive the corresponding screened Coulomb potential energy. That way atomic excitations and deformations of the fusing atoms can be taken into account. Those potentials are then treated semiclassically in order to obtain the screening (accelerating) factor of the reaction. By means of the proposed model the effect of a superstrong magnetic field on laboratory Hydrogen fusion reactions is investigated here for the first time showing that, despite the considerable increase in the cross section of the dd reaction, the pp reaction is still too slow to justify experimentation. The proposed model is finally applied on the H 2 (d, p) H 3 fusion reaction describing satisfactorily the experimental data although some ambiguity remains regarding the molecular nature of the deuteron target. Notably, the present method gives a sufficiently high screening energy for Hydrogen fusion reactions so that the take-away energy of the spectator nucleus can also be taken into account. PACS number(s): 25.10.+s, 25.45.-z

Multi-electron screening effects encountered in laboratory astrophysical reactions are investigated by considering the reactants Thomas-Fermi atoms. By means of that model , previous studies are extended to derive the corresponding screening enhancement factor (SEF), so that it takes into account ionization, thermal, exchange and relativistic effects. The present study, by imposing a very satisfactory constraint on the possible values of the screening energies and the respective SEFs, corrects the current (and the future) experimental values of the astrophysical factors associated with nuclear reactions involved in advanced stages of stellar evolution.

Effective astrophysical factors for non-resonant astrophysical nuclear reaction are usually calculated with respect to a zero energy limit. In the present work that limit is shown to be very disadvantageous compared to the more natural effective energy limit. The latter is used in order to modify the thermonuclear reaction rate formula in stellar evolution codes so that it takes into account both plasma and laboratory screening effects.PACS number(s): 25.60. Pj, 25.40.Lw,24.50.+g, 26.65.+t