11,204 research outputs found
Symmetric coupling of angular momenta, quadratic algebras and discrete polynomials
Eigenvalues and eigenfunctions of the volume operator, associated with the
symmetric coupling of three SU(2) angular momentum operators, can be analyzed
on the basis of a discrete Schroedinger-like equation which provides a
semiclassical Hamiltonian picture of the evolution of a `quantum of space', as
shown by the authors in a recent paper. Emphasis is given here to the
formalization in terms of a quadratic symmetry algebra and its automorphism
group. This view is related to the Askey scheme, the hierarchical structure
which includes all hypergeometric polynomials of one (discrete or continuous)
variable. Key tool for this comparative analysis is the duality operation
defined on the generators of the quadratic algebra and suitably extended to the
various families of overlap functions (generalized recoupling coefficients).
These families, recognized as lying at the top level of the Askey scheme, are
classified and a few limiting cases are addressed.Comment: 10 pages, talk given at "Physics and Mathematics of Nonlinear
Phenomena" (PMNP2013), to appear in J. Phys. Conf. Serie
Diffuse cosmic rays shining in the Galactic center: A novel interpretation of H.E.S.S. and Fermi-LAT gamma-ray data
We present a novel interpretation of the -ray diffuse emission
measured by Fermi-LAT and H.E.S.S. in the Galactic center (GC) region and the
Galactic ridge (GR). In the first part we perform a data-driven analysis based
on PASS8 Fermi-LAT data: we extend down to few GeV the spectra measured by
H.E.S.S. and infer the primary cosmic-ray (CR) radial distribution between 0.1
and 3 TeV. In the second part we adopt a CR transport model based on a
position-dependent diffusion coefficient. Such behavior reproduces the radial
dependence of the CR spectral index recently inferred from the Fermi-LAT
observations. We find that the bulk of the GR emission can be naturally
explained by the interaction of the diffuse steady-state Galactic CR sea with
the gas present in the Central Molecular Zone. Although our results leave room
for a residual radial-dependent emission associated with a central source, the
relevance of the large-scale background prevents from a solid evidence of a GC
Pevatron.Comment: 5 pages, 3 figures, accepted for publication in Physical Review
Letter
How many Ultra High Energy Cosmic Rays could we expect from Centaurus A?
The Pierre Auger Observatory has associated a few ultra high energy cosmic
rays with the direction of Centaurus A. This source has been deeply studied in
radio, infrared, X-ray and -rays (MeV-TeV) because it is the nearest
radio-loud active galactic nuclei.
Its spectral energy distribution or spectrum shows two main peaks, the low
energy peak, at an energy of eV, and the high energy peak, at about
150 keV.
There is also a faint very high energy (E 100 GeV) -ray
emission fully detected by the High Energy Stereoscopic System experiment. In
this work we describe the entire spectrum, the two main peaks with a
Synchrotron/Self-Synchrotron Compton model and, the Very High Energy emission
with a hadronic model. We consider p and interactions. For the
p interaction, we assume that the target photons are those produced at
150 keV in the leptonic processes. On the other hand, for the pp interaction we
consider as targets the thermal particle densities in the lobes. Requiring a
satisfactory description of the spectra at very high energies with p
interaction we obtain an excessive luminosity in ultra high energy cosmic rays
(even exceeding the Eddington luminosity). However, when considering pp
interaction to describe the -spectrum, the obtained number of ultra
high energy cosmic rays are in agreement with Pierre Auger observations.
Moreover, we calculate the possible neutrino signal from pp interactions on a
Km neutrino telescope using Monte Carlo simulations.Comment: Accepted in Ap
Study of TeV variability of Mrk 421 from 3 years of monitoring with the Milagro Observatory
The Milagro experiment was a TeV gamma-ray observatory designed to
continuously monitor the overhead sky in the 0.1-100 TeV energy range. It
operated from 2000 and 2008 and was characterized by a large field of view
( 2 sr) and a high duty cycle ( 90). Here we report on the
long-term monitoring of the blazar Mrk 421 with Milagro over the period from
September 21, 2005 to March 15, 2008. We present a study of the TeV variability
of the source and provide upper limits for the measured flux for different time
scales, ranging from one week up to one year.Comment: 3 pages, 2 figures. Paper to appear in the Proceedings of the
Thirteen Marcel Grossmann Meeting, held in Stockholm, Sweden, on July 2012,
World Scientific, Singapore, in pres
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