17,795 research outputs found
Utterance Selection Model of Language Change
We present a mathematical formulation of a theory of language change. The
theory is evolutionary in nature and has close analogies with theories of
population genetics. The mathematical structure we construct similarly has
correspondences with the Fisher-Wright model of population genetics, but there
are significant differences. The continuous time formulation of the model is
expressed in terms of a Fokker-Planck equation. This equation is exactly
soluble in the case of a single speaker and can be investigated analytically in
the case of multiple speakers who communicate equally with all other speakers
and give their utterances equal weight. Whilst the stationary properties of
this system have much in common with the single-speaker case, time-dependent
properties are richer. In the particular case where linguistic forms can become
extinct, we find that the presence of many speakers causes a two-stage
relaxation, the first being a common marginal distribution that persists for a
long time as a consequence of ultimate extinction being due to rare
fluctuations.Comment: 21 pages, 17 figure
The GeV Excess Shining Through: Background Systematics for the Inner Galaxy Analysis
Recently, a spatially extended excess of gamma rays collected by the
Fermi-LAT from the inner region of the Milky Way has been detected by different
groups and with increasingly sophisticated techniques. Yet, any final
conclusion about the morphology and spectral properties of such an extended
diffuse emission are subject to a number of potentially critical uncertainties,
related to the high density of cosmic rays, gas, magnetic fields and abundance
of point sources. We will present a thorough study of the systematic
uncertainties related to the modelling of diffuse background and to the
propagation of cosmic rays in the inner part of our Galaxy. We will test a
large set of models for the Galactic diffuse emission, generated by varying the
propagation parameters within extreme conditions. By using those models in the
analysis of Fermi-LAT data as Galactic foreground, we will show that the
gamma-ray excess survives and we will quantify the uncertainties affecting the
excess morphology and energy spectrum.Comment: 2014 Fermi Symposium proceedings - eConf C14102.1 7 pages, 4 figure
A Hadronic Scenario for the Galactic Ridge
Several observations from Fermi-LAT, up to few hundred GeV, and from
H.E.S.S., up to 10 TeV, reported an intense -ray emission from
the inner part of the Galactic plane. After the subtraction of point-like
contributions, the remaining -ray spectrum can provide important hints
about the cosmic-ray (CR) population in that region. In particular, the diffuse
spectrum measured by both Fermi-LAT and H.E.S.S. in the Galactic Ridge is
significantly harder with respect to the rest of the Galaxy. These results were
recently interpreted in terms of a comprehensive CR transport model which,
adopting a spatial dependent diffusion coefficient and convective velocity,
reproduces Fermi-LAT results on the whole sky as well as local CR spectra. We
showed as that model predicts a significantly harder neutrino diffuse emission
compared to conventional scenarios: The predicted signal is able to account for
a significant fraction of the astrophysical flux measured by IceCube. In this
contribution, we use the same setup to calculate the expected neutrino flux
from several windows in the inner Galactic plane and compare the results with
IceCube observations and the sensitivities of Mediterranean neutrino
telescopes. In particular, for the ANTARES experiment, we compare the model
expectations with the upper limits obtained from a recent unblinded
data-analysis focused on the galactic ridge region. Moreover, we also show the
expectations from the galactic ridge for the future KM3NeT observatory, whose
position is optimal to observe this portion of the sky.Comment: Oral contribution to the 34th International Cosmic Ray Conference,
July 30 to August 6, The Hague, Netherland
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