483 research outputs found
Nucleon contribution to the induced charge of neutrinos in a matter background and a magnetic field
We study the nucleon contribution to the electromagnetic vertex function of
neutrinos that propagate in a matter background in the presence of a magnetic
field. Starting from the one-loop expression for the corresponding terms of the
vertex function, and taking into account the anomalous magnetic coupling of the
nucleons, we calculate the B-dependent part of the form factors that determine
the induced charge of the neutrino. A formula for the neutrino induced charge
is obtained, and it is evaluated for various illustrative situations. The terms
due to the nucleons can be important in some cases, depending on the physical
conditions of the environment.Comment: revtex4, 13 pages. Contains the minor revisions made in the prd
accepted versio
Ultra-high energy nuclei source in the direction to Virgo cluster
The significant anisotropy in the arrival directions of the 69 events with
energy E> 55 EeV detected by Pierre Auger collaboration is located in the
20-degree region centered near Cen A. Not only the 2-point, but also the
3-point and 4-point autocorrelation functions are completely saturated by this
region. Besides there is an deficit of events in the direction of Virgo
cluster. If one assumes that the excess around Cen A is due to heavy nuclei
shifted from Virgo, one can explain 20-degree scale of this anomaly. Also
location of the highest energy event between the Cen A region and the Virgo
cluster supports this idea. Magnitude and direction of the magnetic field is
similar in this case to those expected for Galactic models. The existence of
nuclei sources in the sky opens the road for a self-consistent description of
Auger data.Comment: 4 pages, 3 figure
Constraints on top-down models for the origin of UHECRs from the Pierre Auger Observatory data
Taking into account the Pierre Auger Observatory limits on the photon
fraction among the highest energy cosmic rays, we show that the models based on
the decay of super-heavy dark matter in the halo of our Galaxy are essentially
excluded from being the sources of UHECRs unless their contribution becomes
significant only above 100 EeV. Some top-down models based on topological
defects are however compatible with the current data and may be best
constrained in the future by the high-energy neutrino flux limit.Comment: Contribution to the 30th International Cosmic Ray Conference, Merida,
Mexico, July 200
Galactic and extragalactic contributions to the astrophysical muon neutrino signal
Spectral and anisotropy properties of IceCube astrophysical neutrino signal
reveal an evidence for a significant Galactic contribution to the neutrino flux
in Southern hemisphere. We check if the Galactic contribution is detectable in
the astrophysical muon neutrino flux observed from a low positive declinations
region of the Northern sky. Estimating the Galactic neutrino flux in this part
of the sky from gamma-ray and Southern sky neutrino data, we find that the
Northern sky astrophysical muon neutrino signal shows an excess over the
Galactic flux. This points to the presence of an additional hard spectrum
(extragalactic or large scale Galactic halo) component of astrophysical
neutrino flux. We show that the Galactic flux component should still be
detectable in the muon neutrino data in a decade long IceCube exposure.Comment: 4 pages, 3 figure
Galactic sources of E>100 GeV gamma-rays seen by Fermi telescope
We perform a search for sources of gamma-rays with energies E>100 GeV at low
Galactic latitudes |b|<10 deg using the data of Fermi telescope. To separate
compact gamma-ray sources from the diffuse emission from the Galaxy, we use the
Minimal Spanning Tree method with threshold of 5 events in inner Galaxy
(Galactic longitude |l|<60 deg) and of 3 events in outer Galaxy. Using this
method, we identify 22 clusters of very-high-energy (VHE) gamma-rays, which we
consider as "source candidates". 3 out of 22 event clusters are expected to be
produced in result of random coincidences of arrival directions of diffuse
background photons. To distinguish clusters of VHE events produced by real
sources from the background we perform likelihood analysis on each source
candidate. We present a list of 19 higher significance sources for which the
likelihood analysis in the energy band E>100 GeV gives Test Statistics (TS)
values above 25. Only 10 out of the 19 high-significance sources can be readily
identified with previously known VHE gamma-ray sources. 4 sources could be
parts of extended emission from known VHE gamma-ray sources. Five sources are
new detections in the VHE band. Among these new detections we tentatively
identify one source as a possible extragalactic source PMN J1603-4904 (a blazar
candidate), one as a pulsar wind nebula around PSR J1828-1007. High
significance cluster of VHE events is also found at the position of a source
coincident with the Eta Carinae nebula. In the Galactic Center region, strong
VHE gamma-ray signal is detected from Sgr C molecular cloud, but not from the
Galactic Center itself.Comment: 6 pages, 2 figure
Evidence for the Galactic contribution to the IceCube astrophysical neutrino flux
We show that the Galactic latitude distribution of IceCube astrophysical
neutrino events with energies above 100~TeV is inconsistent with the isotropic
model of the astrophysical neutrino flux. Namely, the Galactic latitude
distribution of the events shows an excess at low latitudes |b|<10 degrees and
a deficit at high Galactic latitude |b|> 50 degrees. We use Monte-Carlo
simulations to show that the inconsistency of the isotropic signal model with
the data is at > 3 sigma level, after the account of trial factors related to
the choice of the low-energy threshold and Galactic latitude binning in our
analysis.Comment: 4 pages, 2 figures, accepted to Astroparticle Physic
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