7,526 research outputs found
Electronic and atomic kinetics in solids irradiated with free-electron lasers or swift-heavy ions
In this brief review we discuss the transient processes in solids under
irradiation with femtosecond X-ray free-electron-laser (FEL) pulses and
swift-heavy ions (SHI). Both kinds of irradiation produce highly excited
electrons in a target on extremely short timescales. Transfer of the excess
electronic energy into the lattice may lead to observable target modifications
such as phase transitions and damage formation. Transient kinetics of material
excitation and relaxation under FEL or SHI irradiation are comparatively
discussed. The same origin for the electronic and atomic relaxation in both
cases is demonstrated. Differences in these kinetics introduced by the
geometrical effects ({\mu}m-size of a laser spot vs nm-size of an ion track)
and initial irradiation (photoabsorption vs an ion impact) are analyzed. The
basic mechanisms of electron transport and electron-lattice coupling are
addressed. Appropriate models and their limitations are presented.
Possibilities of thermal and nonthermal melting of materials under FEL and SHI
irradiation are discussed
Strong decays of radially excited mesons in a chiral approach
We study radial excitations of pseudoscalar and vector (q bar q) mesons
within a chiral approach. We derive a general form for a chiral Lagrangian
describing processes involving excited pseudoscalar and vector mesons. The
parameters of the chiral Lagrangian are fitted using data and previous
calculations in the framework of the 3P0 model. Finite-width effects are
examined and predictions for mesons previously not discussed are given.
Available experimental data is analyzed whenever possible. Possible hints for
exotic mesons and open interpretation-issues are discussed.Comment: 16 page
Comment on "Exact results for survival probability in the multistate Landau-Zener model"
We correct the proof of Brundobler-Elser formula (BEF) provided in [2004
\textit{J. Phys. B: At. Mol. Opt. Phys.} \textbf{37} 4069] and continued in
Appendix of [2005 \textit{J. Phys. B: At. Mol. Opt. Phys.} \textbf{38} 907].
After showing that some changes of variables employed in these articles are
used erroneously, we propose an alternative change of variables which solves
the problem. In our proof, we reveal the connection between the BEF for a
general -level Landau-Zener system and the exactly solvable bow-tie model.
The special importance of the diabatic levels with maximum/minimum slope is
emphasized throughout.Comment: 10 page
Molecular-Kinetic Simulations of Escape from the Ex-planet and Exoplanets: Criterion for Transonic Flow
The equations of gas dynamics are extensively used to describe atmospheric
loss from solar system bodies and exoplanets even though the boundary
conditions at infinity are not uniquely defined. Using molecular-kinetic
simulations that correctly treat the transition from the continuum to the
rarefied region, we confirm that the energy-limited escape approximation is
valid when adiabatic expansion is the dominant cooling process. However, this
does not imply that the outflow goes sonic. In fact in the sonic regime, the
energy limited approximation can significantly under estimate the escape rate.
Rather large escape rates and concomitant adiabatic cooling can produce
atmospheres with subsonic flow that are highly extended. Since this affects the
heating rate of the upper atmosphere and the interaction with external fields
and plasmas, we give a criterion for estimating when the outflow goes transonic
in the continuum region. This is applied to early terrestrial atmospheres,
exoplanet atmospheres, and the atmosphere of the ex-planet, Pluto, all of which
have large escape rates. The paper and its erratum, combined here, are
published: ApJL 768, L4 (2013); ApJ, 779, L30 (2013).Comment: 11 pages, 3 figure
Gravitational-Recoil Effects on Fermion Propagation in Space-Time Foam
Motivated by the possible experimental opportunities to test quantum gravity
via its effects on high-energy neutrinos propagating through space-time foam,
we discuss how to incorporate spin structures in our D-brane description of
gravitational recoil effects in vacuo. We also point to an interesting
analogous condensed-matter system. We use a suitable supersymmetrization of the
Born-Infeld action for excited D-brane gravitational backgrounds to argue that
energetic fermions may travel slower than the low-energy velocity of light:
\delta c / c \sim -E/M. It has been suggested that Gamma-Ray Bursters may emit
pulses of neutrinos at energies approaching 10^{19} eV: these would be
observable only if M \gsim 10^{27} GeV.Comment: 18 pages LaTe
Production of pair in electron-positron annihilation in the Nambu-Jona-Lasinio model
The process is described in the framework of the
expanded NJL model in the energy region from 0.9 GeV to 1.5 GeV. The
contribution of intermediate state with vector mesons , and , where is the first radial
excitation of - meson was taken into account. Results obtained are in
satisfactory agreement with experimental data.Comment: 5 pages, 1 figure, 1 tabl
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