977 research outputs found
Tandem-pumped ytterbium-doped aluminosilicate fiber amplifier with low quantum defect
We show theoretically that a quantum-defect below 1% is possible in tandem-pumped Yb-doped aluminosilicate fibers operating off the gain peak. Experimentally, we reach a quantum defect of 2% and a slope efficiency of 90% or more
Cross sections for Coulomb and nuclear breakup of three-body halo nuclei
All possible dissociation cross sections for the loosely bound three-body
halo nuclei He (n+n+) and Li (n+n+Li) are computed as
functions of target and beam energy. Both Coulomb and nuclear interactions are
included in the same theoretical framework. The measurements agree with the
calculations for energies above 100 Mev/nucleon. The largest cross sections
correspond to final states with zero or three particles for heavy and with two
neutrons for light targets.Comment: 5 pages, 3 figures, revte
The Pauli principle in a three-body cluster model and the momentum distributions after fragmentation of 6He and 11Li
We investigate two simple prescriptions to account for the Pauli principle in
a three-body cluster model employing a new method based on an adiabatic
hyperspherical expansion to solve the Faddeev equations in coordinate space.
The resulting wave functions are computed and compared. They are furthermore
tested on halo nuclei by calculations of momentum distributions and invariant
mass spectra arising after fragmentation of fast He and Li in
collisions with light targets. The prescriptions are very accurate and the
available measured quantities are remarkably well reproduced when final state
interactions are included.Comment: 18 pages, LaTex file, 15 postscript figures included using epsf.st
A twistor-like D=10 superparticle action with manifest N=8 world-line supersymmetry
We propose a new formulation of the Brink-Schwarz superparticle which
is manifestly invariant under both the target-space super-Poincar\'e group and
the world-line local superconformal group. This twistor-like construction
naturally involves the sphere as a coset space of the Lorentz
group. The action contains only a finite set of auxiliary fields, but they
appear in unusual trilinear combinations. The origin of the on-shell
fermionic symmetry of the standard Brink-Schwarz formulation is
explained. The coupling to a super-Maxwell background requires a new
mechanism, in which the electric charge appears only on shell as an integration
constant.Comment: 22pages, standard LATEX fil
Multi-Phonon -Vibrational Bands and the Triaxial Projected Shell Model
We present a fully quantum-mechanical, microscopic, unified treatment of
ground-state band and multi-phonon -vibrational bands using shell model
diagonalization with the triaxial projected shell model. The results agree very
well with data on the g- and -band spectra in Er, as well
as with recently measured 2-phonon -bandhead energies in
Er and Er. Multi-phonon -excitation energies are
predicted.Comment: 4 pages, 4 figures, submitted to Phys. Lett.
Comprehensive calculations of three--body breakup cross sections
We present in detail a theoretical model for fragmentation reactions of
three--body halo nuclei. The different reaction mechanisms corresponding to the
different processes are described and discussed. Coulomb and nuclear
interactions are simultaneously included and the method is therefore applicable
for any target, light, intermediate and heavy. Absolute values of many
differential cross sections are then available as function of beam energy and
target. We apply the method to fragmentation of He and Li on C, Cu
and Pb. A large variety of observables, cross sections and momentum
distributions, are computed. In almost all cases we obtain good agreement with
the available experimental data.Comment: 41 pages, 10 figures, to be published in Nucl. Phys.
Probing quantum gravity using photons from a flare of the active galactic nucleus Markarian 501 observed by the MAGIC telescope
We analyze the timing of photons observed by the MAGIC telescope during a
flare of the active galactic nucleus Mkn 501 for a possible correlation with
energy, as suggested by some models of quantum gravity (QG), which predict a
vacuum refractive index \simeq 1 + (E/M_{QGn})^n, n = 1,2. Parametrizing the
delay between gamma-rays of different energies as \Delta t =\pm\tau_l E or
\Delta t =\pm\tau_q E^2, we find \tau_l=(0.030\pm0.012) s/GeV at the 2.5-sigma
level, and \tau_q=(3.71\pm2.57)x10^{-6} s/GeV^2, respectively. We use these
results to establish lower limits M_{QG1} > 0.21x10^{18} GeV and M_{QG2} >
0.26x10^{11} GeV at the 95% C.L. Monte Carlo studies confirm the MAGIC
sensitivity to propagation effects at these levels. Thermal plasma effects in
the source are negligible, but we cannot exclude the importance of some other
source effect.Comment: 12 pages, 3 figures, Phys. Lett. B, reflects published versio
Search for the glueball candidates f0(1500) and fJ(1710) in gamma gamma collisions
Data taken with the ALEPH detector at LEP1 have been used to search for gamma
gamma production of the glueball candidates f0(1500) and fJ(1710) via their
decay to pi+pi-. No signal is observed and upper limits to the product of gamma
gamma width and pi+pi- branching ratio of the f0(1500) and the fJ(1710) have
been measured to be Gamma_(gamma gamma -> f0(1500)). BR(f0(1500)->pi+pi-) <
0.31 keV and Gamma_(gamma gamma -> fJ(1710)). BR(fJ(1710)->pi+pi-) < 0.55 keV
at 95% confidence level.Comment: 10 pages, 3 figure
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