241 research outputs found
Physical origin of "chaoticity" of neutrino asymmetry
We consider the indeterminacy in the sign of the neutrino asymmetry generated
by active-sterile neutrino oscillations in the early universe. The dynamics of
asymmetry growth is discussed in detail and the indeterminacy in the final sign
of the asymmetry is shown to be a real physical phenomenon. Recently published
contradicting results are carefully considered and the underlying assumptions
leading to the disagreement are resolved.Comment: 12 pages, Latex, 4 eps figures, uses cite.st
The Effective Matter Potential for Highly Relativistic Neutrinos
We investigate matter effects on highly relativistic neutrinos. The
self-energy of neutrinos is determined in an electron or neutrino background
taking into account resonance and finite width effects of the gauge bosons. We
find minor changes compared to the formerly used formula for the propagator
function and large deviations of the effective width from the decay width of
the gauge bosons considering higher moments of the electron or neutrino
distribution function.Comment: 10 pages, 4 figures, latex. Final version published in Phys. Lett.
Lepton asymmetry creation in the Early Universe
Oscillations of active to sterile neutrinos with a small mixing angle sin 2
\theta < 10^{-2} could generate a large lepton asymmetry in the Early Universe.
The final order of magnitude of the lepton asymmetry \eta is mainly determined
by its growth in the last stage of evolution, the so called power-law regime.
There exist two contradictory results in the literature, \eta \propto T^{-1}
and \eta \propto T^{-4}, where T is the background medium temperature. In the
first case, the lepton asymmetry does not exceed values of 10^{-4} for |\delta
m^2| < 1 eV^2, while in the second case it can become larger than 10^{-1}. In
this work we analytically investigate the case \eta \propto T^{-1}, using a new
approach to solve the kinetic equations. We find that the power-law solution
\eta \propto T^{-1} is not self-consistent. Instead, we find the power law \eta
\propto T^{-11/3} to be a good approximation, which leads to a large final
asymmetry.Comment: 33 pp, 7 figure
Tunneling in a very slow ion-molecule reaction
Quantum tunneling reactions play a significant role in chemistry when
classical pathways are energetically forbidden, be it in gas phase reactions,
surface diffusion, or liquid phase chemistry. In general, such tunneling
reactions are challenging to calculate theoretically, given the high
dimensionality of the quantum dynamics, and also very difficult to identify
experimentally. Hydrogenic systems, however, allow for accurate
first-principles calculations. In this way the rate of the gas phase proton
transfer tunneling reaction of hydrogen molecules with deuterium anions, H_2 +
D^- --> H^- + HD, has been calculated, but has so far lacked experimental
verification. Here we present high-sensitivity measurements of the reaction
rate carried out in a cryogenic 22-pole ion trap. We observe an extremely low
rate constant of (5.2 +- 1.6) x 10^(-20) cm^3/s. This measured value agrees
with quantum tunneling calculations, serving as a benchmark for molecular
theory and advancing the understanding of fundamental collision processes. A
deviation of the reaction rate from linear scaling, which is observed at high
H_2 densities, can be traced back to previously unobserved heating dynamics in
radiofrequency ion traps
High energy neutrino spin light
The quantum theory of spin light (electromagnetic radiation emitted by a
Dirac massive neutrino propagating in dense matter due to the weak interaction
of a neutrino with background fermions) is developed. In contrast to the
Cherenkov radiation, this effect does not disappear even if the medium
refractive index is assumed to be equal to unity. The formulas for the
transition rate and the total radiation power are obtained. It is found out
that radiation of photons is possible only when the sign of the particle
helicity is opposite to that of the effective potential describing the
interaction of a neutrino (antineutrino) with the background medium. Due to the
radiative self-polarization the radiating particle can change its helicity. As
a result, the active left-handed polarized neutrino (right-handed polarized
antineutrino) converting to the state with inverse helicity can become
practically ``sterile''. Since the sign of the effective potential depends on
the neutrino flavor and the matter structure, the spin light can change a ratio
of active neutrinos of different flavors. In the ultra relativistic approach,
the radiated photons averaged energy is equal to one third of the initial
neutrino energy, and two thirds of the energy are carried out by the final
``sterile'' neutrinos.Comment: 12 pages, Latex. To appear in Phys. Lett.
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