3,250 research outputs found
Quantum uncertainty in weakly non-ideal astrophysical plasma
Galitskii and Yakimets showed that in dense or low temperature plasma, due to quantum uncertainty effect, the particle distribution function over momenta acquires a power-like tail even under conditions of thermodynamic equilibrium. We show that in weakly non-ideal plasmas, like the solar interior, both non-extensivity and quantum uncertainty should be taken into account to derive equilibrium ion distribution functions and to estimate nuclear reaction rates and solar neutrino fluxes. The order of magnitude of the deviation from the standard Maxwell-Boltzmann distribution can be derived microscopically by considering the presence of random electrical microfield in the stellar plasma. We show that such a nonextensive statistical effect can be very relevant in many nuclear astrophysical problems
Collisional cross sections and momentum distributions in astrophysical plasmas: dynamics and statistical mechanics link
We show that, in stellar core plasmas, the one-body momentum distribution
function is strongly dependent, at least in the high velocity regime, on the
microscopic dynamics of ion elastic collisions and therefore on the effective
collisional cross sections, if a random force field is present. We take into
account two cross sections describing ion-dipole and ion-ion screened
interactions. Furthermore we introduce a third unusual cross section, to link
statistical distributions and a quantum effect originated by the
energy-momentum uncertainty owing to many-body collisions, and propose a
possible physical interpretation in terms of a tidal-like force. We show that
each collisional cross section gives rise to a slight peculiar correction on
the Maxwellian momentum distribution function in a well defined velocity
interval. We also find a possible link between microscopical dynamics of ions
and statistical mechanics interpreting our results in the framework of
non-extensive statistical mechanics.Comment: 8 page
Solar reaction rates, non-extensivity and quantum uncertainty
We show that in weakly non-ideal plasmas, like the solar interior, both
non-extensivity and quantum uncertainty (a' la Galitskii and Yakimets) should
be taken into account to derive equilibrium ion distribution functions and to
estimate nuclear reaction rates and solar neutrino fluxes.Comment: 8 pages, revte
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
Enhancement of fusion rates due to quantum effects in the particles momentum distribution in nonideal media
This study concerns a situation when measurements of the nonresonant
cross-section of nuclear reactions appear highly dependent on the environment
in which the particles interact. An appealing example discussed in the paper is
the interaction of a deuteron beam with a target of deuterated metal Ta. In
these experiments, the reaction cross section for d(d,p)t was shown to be
orders of magnitude greater than what the conventional model predicts for the
low-energy particles. In this paper we take into account the influence of
quantum effects due to the Heisenberg uncertainty principle for particles in a
non-ideal medium elastically interacting with the medium particles. In order to
calculate the nuclear reaction rate in the non-ideal environment we apply both
the Monte Carlo technique and approximate analytical calculation of the Feynman
diagram using nonrelativistic kinetic Green's functions in the medium which
correspond to the generalized energy and momentum distribution functions of
interacting particles. We show a possibility to reduce the 12-fold integral
corresponding to this diagram to a fivefold integral. This can significantly
speed up the computation and control accuracy. Our calculations show that
quantum effects significantly influence reaction rates such as p +7Be, 3He
+4He, p +7Li, and 12C +12C. The new reaction rates may be much higher than the
classical ones for the interior of the Sun and supernova stars. The possibility
to observe the theoretical predictions under laboratory conditions is
discussed
On quantum plasma: a plea for a common sense
The quantum plasma theory has flourished in the past few years without much
regard to the physical validity of the formulation or its connection to any
real physical system. It is argued here that there is a very limited physical
ground for the application of such a theory.Comment: EPL, to be published 201
Dispersion properties of electrostatic oscillations in quantum plasmas
We present a derivation of the dispersion relation for electrostatic
oscillations (ESOs) in a zero temperature quantum plasma. In the latter,
degenerate electrons are governed by the Wigner equation, while non-degenerate
ions follow the classical fluid equations. The Poisson equation determines the
electrostatic wave potential. We consider parameters ranging from semiconductor
plasmas to metallic plasmas and electron densities of compressed matter such as
in laser-compression schemes and dense astrophysical objects. Due to the wave
diffraction caused by overlapping electron wave function due to the Heisenberg
uncertainty principle in dense plasmas, we have possibility of Landau damping
of the high-frequency electron plasma oscillations (EPOs) at large enough
wavenumbers. The exact dispersion relations for the EPOs are solved numerically
and compared to the ones obtained by using approximate formulas for the
electron susceptibility in the high- and low-frequency cases.Comment: 9 pages, 3 figures. Accepted for publication in Journal of Plasma
Physic
External Fields as a Probe for Fundamental Physics
Quantum vacuum experiments are becoming a flexible tool for investigating
fundamental physics. They are particularly powerful for searching for new light
but weakly interacting degrees of freedom and are thus complementary to
accelerator-driven experiments. I review recent developments in this field,
focusing on optical experiments in strong electromagnetic fields. In order to
characterize potential optical signatures, I discuss various low-energy
effective actions which parameterize the interaction of particle-physics
candidates with optical photons and external electromagnetic fields.
Experiments with an electromagnetized quantum vacuum and optical probes do not
only have the potential to collect evidence for new physics, but
special-purpose setups can also distinguish between different particle-physics
scenarios and extract information about underlying microscopic properties.Comment: 12 pages, plenary talk at QFEXT07, Leipzig, September 200
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