23,940 research outputs found
On the Application of Gluon to Heavy Quarkonium Fragmentation Functions
We analyze the uncertainties induced by different definitions of the momentum
fraction in the application of gluon to heavy quarkonium fragmentation
function. We numerically calculate the initial fragmentation
functions by using the non-covariant definitions of with finite gluon
momentum and find that these fragmentation functions have strong dependence on
the gluon momentum . As , these fragmentation
functions approach to the fragmentation function in the light-cone definition.
Our numerical results show that large uncertainties remains while the
non-covariant definitions of are employed in the application of the
fragmentation functions. We present for the first time the polarized gluon to
fragmentation functions, which are fitted by the scheme exploited in
this work.Comment: 11 pages, 7 figures;added reference for sec.
Universal decay law in charged-particle emission and exotic cluster radioactivity
A linear universal decay formula is presented starting from the microscopic
mechanism of the charged-particle emission. It relates the half-lives of
monopole radioactive decays with the -values of the outgoing particles as
well as the masses and charges of the nuclei involved in the decay. This
relation is found to be a generalization of the Geiger-Nuttall law in
radioactivity and explains well all known cluster decays. Predictions on the
most likely emissions of various clusters are presented.Comment: 2 figure
Black hole production at lepton colliders
Production of black holes has been discussed in a variety of extensions of
the Standard Model, and related bounds have been established from data taken at
the Large Hadron Collider. We show that, if the Higgs particle has a fully
gravitational content via the equivalence principle, enhanced cross-sections of
black holes at colliders should be expected within the Standard Model itself.
The case of black hole production by precision measurements at electron
colliders is discussed. The Coulomb repulsion strongly suppresses the related
cross-section with respect to the one based on the hoop conjecture, making the
possible production of black holes still unfeasible with current beam
technology. At the same time, this suggests the reanalysis of the bounds, based
on the hoop conjecture, already determined in hadronic collisions for
extra-dimensional models.Comment: 10 pages, 6 figure
Local Dielectric Measurements of BaTiO3-CoFe2O4 Nano-composites Through Microwave Microscopy
We report on linear and non-linear dielectric property measurements of BaTiO3
- CoFe2O4 (BTO-CFO) ferroelectro-magnetic nano-composites and pure BaTiO3 and
CoFe2O4 samples with Scanning Near Field Microwave Microscopy. The permittivity
scanning image with spatial resolution on the micro-meter scale shows that the
nano-composites have very uniform quality with an effective dielectric constant
\epsilon_r = 140 +/- 6.4 at 3.8 GHz and room temperature. The temperature
dependence of dielectric permittivity shows that the Curie temperature of pure
BTO was shifted by the clamping effect of the MgO substrate, whereas the Curie
temperature shift of the BTO ferroelectric phase in BTO-CFO composites is less
pronounced, and if it exists at all, would be mainly caused by the CFO.
Non-linear dielectric measurements of BTO-CFO show good ferroelectric
properties from BTO.Comment: 6 pages, 6 figures, to be published in the Journal of Materials
Researc
Calculation of the spectrum of 12Li by using the multistep shell model method in the complex energy plane
The unbound nucleus Li is evaluated by using the multistep shell model
in the complex energy plane assuming that the spectrum is determined by the
motion of three neutrons outside the Li core. It is found that the ground
state of this system consists of an antibound state and that only this
and a and a excited states are physically meaningful
resonances.Comment: 9 pages, 5 tables, 7 figures, printer-friendly versio
Dynamical Axion Field in Topological Magnetic Insulators
Axions are very light, very weakly interacting particles postulated more than
30 years ago in the context of the Standard Model of particle physics. Their
existence could explain the missing dark matter of the universe. However,
despite intensive searches, they have yet to be detected. In this work, we show
that magnetic fluctuations of topological insulators couple to the
electromagnetic fields exactly like the axions, and propose several experiments
to detect this dynamical axion field. In particular, we show that the axion
coupling enables a nonlinear modulation of the electromagnetic field, leading
to attenuated total reflection. We propose a novel optical modulators device
based on this principle.Comment: 5 pages, 3 figure
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