650 research outputs found
Charged Current Neutrino Cross Section and Tau Energy Loss at Ultra-High Energies
We evaluate both the tau lepton energy loss produced by photonuclear
interactions and the neutrino charged current cross section at ultra-high
energies, relevant to neutrino bounds with Earth-skimming tau neutrinos, using
different theoretical and phenomenological models for nucleon and nucleus
structure functions. The theoretical uncertainty is estimated by taking
different extrapolations of the structure function F2 to very low values of x,
in the low and moderate Q2 range for the tau lepton interaction and at high Q2
for the neutrino-nucleus inelastic cross section. It is at these extremely low
values of x where nuclear shadowing and parton saturation effects are unknown
and could be stronger than usually considered. For tau and neutrino energies
E=10^9 GeV we find uncertainties of a factor 4 for the tau energy loss and of a
factor 2 for the charged current neutrino-nucleus cross section.Comment: 20 pages and 11 figure
Signatures of unstable semiclassical trajectories in tunneling
It was found recently that processes of multidimensional tunneling are
generally described at high energies by unstable semiclassical trajectories. We
study two observational signatures related to the instability of trajectories.
First, we find an additional power-law dependence of the tunneling probability
on the semiclassical parameter as compared to the standard case of potential
tunneling. The second signature is substantial widening of the probability
distribution over final-state quantum numbers. These effects are studied using
modified semiclassical technique which incorporates stabilization of the
tunneling trajectories. The technique is derived from first principles. We
obtain expressions for the inclusive and exclusive tunneling probabilities in
the case of unstable semiclassical trajectories. We also investigate the "phase
transition" between the cases of stable and unstable trajectories across
certain "critical" value of energy. Finally, we derive the relation between the
semiclassical probabilities of tunneling from the low-lying and highly excited
initial states. This puts on firm ground a conjecture made previously in the
semiclassical description of collision-induced tunneling in field theory.Comment: Journal version; 48 pages, 16 figure
Measurements of the Casimir-Lifshitz force in fluids: the effect of electrostatic forces and Debye screening
In this work, we present detailed measurements of the Casimir-Lifshitz force
between two gold surfaces (a sphere and a plate) immersed in ethanol and study
the effect of residual electrostatic forces, which are dominated by static
fields within the apparatus and can be reduced with proper shielding.
Electrostatic forces are further reduced by Debye screening through the
addition of salt ions to the liquid. Additionally, the salt leads to a
reduction of the Casimir-Lifshitz force by screening the zero-frequency
contribution to the force; however, the effect is small between gold surfaces
at the measured separations and within experimental error. An improved
calibration procedure is described and compared to previous methods. Finally,
the experimental results are compared to Lifshitz's theory and found to be
consistent for the materials used in the experiment.Comment: 11 figures. PRA in pres
Real-Time Instantons and Suppression of Collision-Induced Tunneling
We consider tunneling processes in QFT induced by collisions of elementary
particles. We propose a semiclassical method for estimating the probability of
these processes in the limit of very high collision energy. As an illustration,
we evaluate the maximum probability of induced tunneling between different
vacua in a (1+1)-dimensional scalar model with boundary interaction.Comment: 5 pages, 1 figure, JETP Letters styl
Use of singular classical solutions for calculation of multiparticle cross sections in field theory
A method of reducing the problem of the calculation of tree multiparticle
cross sections in theory to the solution of a singular classical
Euclidean boundary value problem is introduced. The solutions are obtained
numerically in terms of the decomposition in spherical harmonics, and the
corresponding estimates of the tree cross sections at arbitrary energies are
found. Numerical analysis agrees with analytical results obtained earlier in
the limiting cases of large and small energies.Comment: LaTeX, 18 pages, 3 postscript figure
Air ions induced aerosol sensing by eye-safe LIDAR
Low concentrations aerosols quantification is rather challenging for LIDAR
instruments due to eye-safety restrictions so high energy pulses cannot be
utilized to improve the sensitivity. Highly sensitive but eye-save LIDAR has
been developed for the quantification of the water droplet aerosol which was
induced by air ions. Few days sensing of aerosols in closed tunnel revealed a
strong correlation between air optical transparency (LIDAR measurements) and
concentrations of positive/negative ions (ion counter Sapphir 3-M). The
correlation coefficient was observed to be almost unity for the air
transparency signal and air ions unipolarity coefficient. High sensitivity of
the water droplet aerosol quantification makes the developed eye-safe LIDAR a
perspective instrument for space resolved measurements of the air ions
distribution. Space and time resolved measurements of air ions exhalation can
be a new instrument for tectonic activity study including new earthquake
forecasting indicators search
Predicting Neutron Production from Cosmic-ray Muons
Fast neutrons from cosmic-ray muons are an important background to
underground low energy experiments. The estimate of such background is often
hampered by the difficulty of measuring and calculating neutron production with
sufficient accuracy. Indeed substantial disagreement exists between the
different analytical calculations performed so far, while data reported by
different experiments is not always consistent. We discuss a new unified
approach to estimate the neutron yield, the energy spectrum, the multiplicity
and the angular distribution from cosmic muons using the Monte Carlo simulation
package FLUKA and show that it gives a good description of most of the existing
measurements once the appropriate corrections have been applied.Comment: 8 pages, 7 figure
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