arXiv subjects

Massimo Coraddu

Publications and source records attributed to Massimo Coraddu.

6 recordsLinked to original sources

arXiv2005

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.

nucl-th↗

arXiv2005

Entropy production and Pesin-like identity at the onset of chaos

Asymptotically entropy of chaotic systems increases linearly and the sensitivity to initial conditions is exponential with time: these two behaviors are related. Such relationship is the analogous of and under specific conditions has been shown to coincide with the Pesin identity. Numerical evidences support the proposal that the statistical formalism can be extended to the edge of chaos by using a specific generalization of the exponential and of the Boltzmann-Gibbs entropy. We extend this picture and a Pesin-like identity to a wide class of deformed entropies and exponentials using the logistic map as a test case. The physical criterion of finite-entropy growth strongly restricts the suitable entropies. The nature and characteristics of this generalization are clarified.

cond-mat.stat-mech↗

arXiv2005

What entropy at the edge of chaos?

Numerical experiments support the interesting conjecture that statistical methods be applicable not only to fully-chaotic systems, but also at the edge of chaos by using Tsallis' generalizations of the standard exponential and entropy. In particular, the entropy increases linearly and the sensitivity to initial conditions grows as a generalized exponential. We show that this conjecture has actually a broader validity by using a large class of deformed entropies and exponentials and the logistic map as test cases.

cond-mat.stat-mech↗

arXiv2002

Super-Kamiokande hep neutrino best fit: a possible signal of nonmaxwellian solar plasma

The Super-Kamiokande best global fit, which includes data from SNO, Gallium and Chlorine experiments, results in a hep neutrino contribution to the signals that, even after oscillation, is greater than the SSM prediction. The solar hep neutrino flux that would yield this contribution is four times larger than the one predicted by the SSM. Recent detailed calculations exclude that the astrophysical factor S_{hep}(0) could be wrong by such a large factor. Given the reliability of the temperature and densities profiles inside the Sun, this experimental result indicates that plasma effects are important for this reaction. We show that a slight enhancement of the high-energy tail, enhancement that is of the order of the deviations from the Maxwell-Boltzmann distribution expected in the solar core plasma, produces an increment of the hep rate of the magnitude required. We verified that the other neutrino fluxes remain compatible with experimental signals and SSM predictions. Better measurements of the high-energy tail of the neutrino spectrum would improve our understanding of reaction rates in the solar plasma.

hep-ph↗

arXiv2002

Ultra high energy photon showers in magnetic field:angular distribution of produced particles

Ultra high energy (UHE) photons can initiate electromagnetic showers in magnetic field. We analyze the two processes that determine the development of the shower, $e^+ e^-$ pair creation and synchrotron radiation, and derive formulae for the angular distribution of the produced particles. These formulae are necessary to study the three-dimensional development of the shower.

hep-ph↗

arXiv2001

Deuterium burning in Jupiter interior

We show that moderate deviations from the Maxwell-Boltzmann energy distribution can increase deuterium reaction rates enough to contribute to the heating of Jupiter. These deviations are compatible with the violation of extensivity expected from temperature and density conditions inside Jupiter.

physics.plasm-ph↗