Nuclear astrophysical plasmas: ion distribution functions and fusion rates

This article illustrates how very small deviations from the Maxwellian exponential tail, while leaving unchanged bulk quantities, can yield dramatic effects on fusion reaction rates and discuss several mechanisms that can cause such deviations.Comment: 9 ReVTex pages including 2 color figure

Nonextensive statistical effects on nuclear astrophysics and many-body problems

Density and temperature conditions in many stellar core (like the solar core) imply the presence of nonideal plasma effects with memory and long-range interactions between particles. This aspect suggests the possibility that the stellar core could not be in a global thermodynamical equilibrium but satisfies the conditions of a metastable state with a stationary (nonextensive) power law distribution function among ions. The order of magnitude of the deviation from the standard Maxwell-Boltzmann distribution can be derived microscopically by considering the presence of random electrical microfields in the stellar plasma. We show that such a nonextensive statistical effect can be very relevant in many nuclear astrophysical problems.Comment: 8 pages, Proceedings of the X Convegno su Problemi di Fisica Nucleare Teoric

Nonextensive Interpretation Of Radiative Recombination In Electron Cooling

An interest for the low-energy range of the nonextensive distribution function arises from the study of radiative recombination in electron cooling devices in particle accelerators, whose experimentally measured reaction rates are much above the theoretical prediction. The use of generalized distributions, that differ from the Maxwellian in the low energy part (due to subdiffusion between electron and ion bunches), may account for the observed rate enhancement. In this work, we consider the isotropic distribution function and we propose a possible experiment for verifying the existence of a cut-off in the generalized momentum distribution, by measuring the spectrum of the X-rays emitted from radiative recombination reactions.Comment: 8 pages, 2 figures, Submitted for publication in the Proceedings of the 3rd International Conference NEXT-SigmaPhi, 2005, Cret

Fusion reactions in plasmas as probe of the high-momentum tail of particle distributions

In fusion reactions, the Coulomb barrier selects particles from the high-momentum part of the distribution. Therefore, small variations of the high-momentum tail of the velocity distribution can produce strong effects on fusion rates. In plasmas several potential mechanisms exist that can produce deviations from the standard Maxwell-Boltzmann distribution. Quantum broadening of the energy-momentum dispersion relation of the plasma quasi-particles modifies the high-momentum tail and could explain the fusion-rate enhancement observed in low-energy nuclear reaction experiments.Comment: 9 pages in ReVTeX preprint format, 3 figures, to appear in EPJ

Non-Markovian effects in the solar neutrino problem

The solar core, because of its density and temperature, is not a weakly-interacting or a high-temperature plasma. Collective effects have time scales comparable to the average time between collisions, and the microfield distribution influences the particle dynamics. In this conditions ion and electron diffusion is a non-Markovian process, memory effects are present and the equilibrium statistical distribution function differs from the Maxwellian one. We show that, even if the deviations from the standard velocity distribution that are compatible with our present knowledge of the solar interior are small, they are sufficient to sensibly modify the sub-barrier nuclear reaction rates. The consequent changes of the neutrino fluxes are comparable to the flux deficits that constitute the solar neutrino problem.Comment: 4 pages, to appear in the Proceedings of Nuclei in the Cosmos