91,071 research outputs found
Quantum Decoherence of Photons in the Presence of Hidden U(1)s
Many extensions of the standard model predict the existence of hidden sectors
that may contain unbroken abelian gauge groups. We argue that in the presence
of quantum decoherence photons may convert into hidden photons on sufficiently
long time scales and show that this effect is strongly constrained by CMB and
supernova data. In particular, Planck-scale suppressed decoherence scales D ~
E^2/M_Pl (characteristic for non-critical string theories) are incompatible
with the presence of even a single hidden U(1). The corresponding bounds on the
decoherence scale are four orders of magnitude stronger than analogous bounds
derived from solar and reactor neutrino data and complement other bounds
derived from atmospheric neutrino data.Comment: 8 pages, 9 figure
Geometric Phase for Fermionic Quasiparticles Scattering by Disgyration in Superfluids
We consider a Volovik's analog model for description of a topological defects
in a superfluid and we investigate the scattering of quasiparticles in this
background. The analog of the gravitational Aharonov-Bohm in this system is
found. An analysis of this problem employing loop variables is considered and
corroborates for the existence of the Aharonov-Bohm effect in this system. The
results presented here may be used to study the Aharonov-Bohm effect in
superconductors.Comment: 7 pages, to appear in Europhys. Let
The role of heavy quarks in light hadron fragmentation
We investigate the role of heavy quarks in the production of light flavored
hadrons and in the determination of the corresponding non perturbative
hadronization probabilities. We define a general mass variable flavor number
scheme for fragmentation functions that accounts for heavy quark mass effects,
and perform a global QCD analysis to an up-to-date data set including very
precise Belle and BaBar results. We show that the mass dependent picture
provides a much more accurate and consistent description of data.Comment: 5 pages, 3 eps figure
Gravitational Binding, Virialization and the Peculiar Velocity Distribution of the Galaxies
We examine the peculiar velocity distribution function of galaxies in
cosmological many-body gravitational clustering. Our statistical mechanical
approach derives a previous basic assumption and generalizes earlier results to
galaxies with haloes. Comparison with the observed peculiar velocity
distributions indicates that individual massive galaxies are usually surrounded
by their own haloes, rather than being embedded in common haloes. We then
derive the density of energy states, giving the probability that a randomly
chosen configuration of N galaxies in space is bound and virialized.
Gravitational clustering is very efficient. The results agree well with the
observed probabilities for finding nearby groups containing N galaxies. A
consequence is that our local relatively low mass group is quite typical, and
the observed small departures from the local Hubble flow beyond our group are
highly probable.Comment: Paper in aastex 5.0 format and 9 figures. Replace a new version with
figures and typos correcte
Collapse of the ESR fine structure throughout the coherent temperature of the Gd-doped Kondo Semiconductor
Experiments on the Electron Spin Resonance (ESR) in the filled
skutterudite (), at temperatures
where the host resistivity manifests a smooth insulator-metal crossover,
provides evidence of the underlying Kondo physics associated with this system.
At low temperatures (below ), behaves
as a Kondo-insulator with a relatively large hybridization gap, and the
ESR spectra displays a fine structure with lorentzian line shape,
typical of insulating media. The electronic gap is attributed to the large
hybridization present in the coherent regime of a Kondo lattice, when Ce
4f-electrons cooperate with band properties at half-filling. Mean-field
calculations suggest that the electron-phonon interaction is fundamental at
explaining the strong 4f-electron hybridization in this filled skutterudite.
The resulting electronic structure is strongly temperature dependent, and at
about the system undergoes an insulator-to-metal
transition induced by the withdrawal of 4f-electrons from the Fermi volume, the
system becoming metallic and non-magnetic. The ESR fine structure
coalesces into a single dysonian resonance, as in metals. Still, our
simulations suggest that exchange-narrowing via the usual Korringa mechanism,
alone, is not capable of describing the thermal behavior of the ESR spectra in
the entire temperature region ( - K). We propose that temperature
activated fluctuating-valence of the Ce ions is the missing ingredient that,
added to the usual exchange-narrowing mechanism, fully describes this unique
temperature dependence of the ESR fine structure observed in
.Comment: 19 pages, 6 figure
Preface "Nonlinear processes in oceanic and atmospheric flows"
Nonlinear phenomena are essential ingredients in many oceanic and atmospheric
processes, and successful understanding of them benefits from multidisciplinary
collaboration between oceanographers, meteorologists, physicists and
mathematicians. The present Special Issue on ``Nonlinear Processes in Oceanic
and Atmospheric Flows'' contains selected contributions from attendants to the
workshop which, in the above spirit, was held in Castro Urdiales, Spain, in
July 2008. Here we summarize the Special Issue contributions, which include
papers on the characterization of ocean transport in the Lagrangian and in the
Eulerian frameworks, generation and variability of jets and waves, interactions
of fluid flow with plankton dynamics or heavy drops, scaling in meteorological
fields, and statistical properties of El Ni\~no Southern Oscillation.Comment: This is the introductory article to a Special Issue on "Nonlinear
Processes in Oceanic and Atmospheric Flows'', published in the journal
Nonlinear Processes in Geophysics, where the different contributions are
summarized. The Special Issue itself is freely available from
http://www.nonlin-processes-geophys.net/special_issue103.htm
- …