280 research outputs found
Deformed logarithms and entropies
By solving a differential-functional equation inposed by the MaxEnt principle
we obtain a class of two-parameter deformed logarithms and construct the
corresponding two-parameter generalized trace-form entropies. Generalized
distributions follow from these generalized entropies in the same fashion as
the Gaussian distribution follows from the Shannon entropy, which is a special
limiting case of the family. We determine the region of parameters where the
deformed logarithm conserves the most important properties of the logarithm,
and show that important existing generalizations of the entropy are included as
special cases in this two-parameter class.Comment: Presented at next2003, Second Sardinian International Conference on
News and Expectations in Thermostatistics, Villasimius (Cagliari) Italy,
21st-28th September 2003. In press Physica A (2004). Elsevier LaTeX macros,
11 pages, 1 figur
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
Thermal distributions in stellar plasmas, nuclear reactions and solar neutrinos
The physics of nuclear reactions in stellar plasma is reviewed with special
emphasis on the importance of the velocity distribution of ions. Then the
properties (density and temperature) of the weak-coupled solar plasma are
analysed, showing that the ion velocities should deviate from the Maxwellian
distribution and could be better described by a weakly-nonexstensive
(|q-1|<0.02) Tsallis' distribution. We discuss concrete physical frameworks for
calculating this deviation: the introduction of higher-order corrections to the
diffusion and friction coefficients in the Fokker-Plank equation, the influence
of the electric-microfield stochastic distribution on the particle dynamics, a
velocity correlation function with long-time memory arising from the coupling
of the collective and individual degrees of freedom. Finally, we study the
effects of such deviations on stellar nuclear rates, on the solar neutrino
fluxes, and on the pp neutrino energy spectrum, and analyse the consequences
for the solar neutrino problem.Comment: ReVTeX, 23 pages, 3 figures, to appear in the special issue
(Nonextensive statistical mechanics and thermodynamics) of the Brazilian
Journal of Physic
Hadron wave functions and the issue of nucleon deformation
Using gauge invariant hadronic two- and three- density correlators we extract
information on the spatial distributions of quarks in hadrons, and on hadron
shape and multipole moments within quenched lattice QCD. Combined with the
calculation of N to Delta transition amplitudes the issue of nucleon
deformation can be addressed.Comment: 4 pages, 7 figures. Talk presented at the PANIC02 conference, Sept.
30 - Oct. 4, 2002, Osaka, Japan. Discussion of the N to Delta results
modifie
Modified Debye-Huckel Electron Shielding and Penetration Factor
Screened potential, modified by non standard electron cloud distributions
responsible for the shielding effect on fusion of reacting nuclei in
astrophysical plasmas, is derived. The case of clouds with depleted tails in
space coordinates is discussed. The modified screened potential is obtained
both from statistical mechanics arguments based on fluctuations of the inverse
of the Debye-Huckel radius and from the solution of a Bernoulli equation used
in generalized statistical mechanics. Plots and tables useful in evaluating
penetration probability at any energy are provided.Comment: 9 pages, 3 figures, 3 table
Two-parameter deformations of logarithm, exponential, and entropy: A consistent framework for generalized statistical mechanics
A consistent generalization of statistical mechanics is obtained by applying
the maximum entropy principle to a trace-form entropy and by requiring that
physically motivated mathematical properties are preserved. The emerging
differential-functional equation yields a two-parameter class of generalized
logarithms, from which entropies and power-law distributions follow: these
distributions could be relevant in many anomalous systems. Within the specified
range of parameters, these entropies possess positivity, continuity, symmetry,
expansibility, decisivity, maximality, concavity, and are Lesche stable. The
Boltzmann-Shannon entropy and some one parameter generalized entropies already
known belong to this class. These entropies and their distribution functions
are compared, and the corresponding deformed algebras are discussed.Comment: Version to appear in PRE: about 20% shorter, references updated, 13
PRE pages, 3 figure
High-energy neutrino conversion into electron-W pair in magnetic field and its contribution to neutrino absorption
We calculate the conversion rate of high-energy neutrinos propagating in
constant magnetic field into an electron-W pair (nu -> W + e) from the
imaginary part of the neutrino self-energy. Using the exact propagators in
constant magnetic field, the neutrino self-energy has been calculated to all
order in the field within the Weinberg-Salam model. We obtain a compact formula
in the limit of B << Bcr = m^2/e. We find that above the process threshold Eth
\~ 2.2 10^16 (Bcr / B) eV this contribution to the absorption of neutrinos
yields an asymptotic absorption length ~ 1.1 (Bcr / B)^2 (10^{16} eV / E)
meters.Comment: 10 pages in RevTeX, 2 figures; published version: two typos
corrected, one reference adde
Nuclear physics inputs needed for geo-neutrino studies
Geo-neutrino studies are based on theoretical estimates of geo-neutrino
spectra. We propose a method for a direct measurement of the energy
distribution of antineutrinos from decays of long-lived radioactive isotopes.Comment: 6 pages, 3 figures. Proceedings of the International Conference on
Topics in Astroparticle and Underground Physics (TAUP) 2007, Sendai, Japan,
September 11-15, 2007. To appear in Journal of Physics: Conference Serie
- …