5,975 research outputs found
On decays of Z' into unparticle stuff
We study the decay of a Z' - boson into U -unparticle and a photon. The
extended Landau-Yang theorem is used. The clear photon signal would make the
decay Z' \rightarrow \gamma U as an additional contribution mode for study of
unparticle physics.Comment: 11 pages, 3 figures, paper accepted for publication by Advances in
High Energy Physics journa
Estimate of the correlation signal between cosmic rays and BL Lacs in future data
The existing correlation between BL Lacertae objects (BL Lacs) and cosmic-ray
events observed by HiRes experiment provide sufficient information to formulate
quantitatively the hypothesis about the flux of neutral cosmic-ray particles
originated from BL Lacs. We determine the potential of future cosmic ray
experiments to test this hypothesis by predicting the number of coincidences
between arrival directions of cosmic rays and positions of BL Lacs on the
celestial sphere, which should be observed in the future datasets. We find that
the early Pierre Auger data will not have enough events to address this
question. On the contrary, the final Pierre Auger data and the early Telescope
Array data will be sufficient to fully test this hypothesis. If confirmed, it
would imply the existence of highest-energy neutral particles coming from
cosmological distances.Comment: 5 page
Novel magnetic phase in a weakly ordered spin-1/2 chain antiferromagnet SrCuO
We present the magnetic phase diagram of a spin-1/2 chain antiferromagnet
SrCuO studied by ultrasound phase-sensitive detection technique. We
observe an enhanced effect of external magnetic field on the ordering
temperature of the system, which is in the extreme proximity to the quantum
critical point. Inside the N\'eel ordered phase, we detect an additional
field-induced continuous phase transition, which is unexpected for a collinear
Heisenberg antiferromagnet. This transition is accompanied by softening of
magnetic excitation mode observed by electron-spin resonance, which can be
associated with a longitudinal (amplitude) mode of the order parameter in a
weakly-coupled system of spin-1/2 chains. These results suggest transition from
a transverse collinear antiferromagnet to an amplitude-modulated spin density
wave phase induced by magnetic field.Comment: 4 pages, 4 figure
Evidence for a connection between the gamma-ray and the highest energy cosmic-ray emissions by BL Lacertae objects
A set of potentially gamma-ray--loud BL Lac objects is selected by
intersecting the EGRET and BL Lac catalogs. Of the resulting 14 objects, eight
are found to correlate with arrival directions of ultra--high-energy cosmic
rays (UHECRs), with significance of the order of 5 sigma. This suggests that
gamma-ray emission can be used as a distinctive feature of those BL Lac objects
that are capable of producing UHECR.Comment: 11 pages, 1 figure, version published in APJ Letter
Testing the correlations between ultra-high-energy cosmic rays and BL Lac type objects with HiRes stereoscopic data
Previously suggested correlations of BL Lac type objects with the arrival
directions of the ultra-high-energy cosmic ray primaries are tested by making
use of the HiRes stereoscopic data. The results of the study support the
conclusion that BL Lacs may be the cosmic ray sources and suggest the presence
of a small (a few percent) fraction of neutral primaries at E>10^{19} eV.Comment: 4 pages, 3 figure
Identification of extragalactic sources of the highest energy EGRET photons by correlation analysis
We found significant correlations between the arrival directions of the
highest energy photons (E>10 GeV) observed by EGRET and positions of the BL Lac
type objects (BL Lacs). The observed correlations imply that not less than
three per cent of extragalactic photons at these energies originate from BL
Lacs. Some of the correlating BL Lacs have no counterparts in the EGRET source
catalog, i.e. do not coincide with strong emitters of gamma-rays at lower
energy. The study of correlating BL Lacs suggests that they may form a subset
which is statistically different from the total BL Lac catalog; we argue that
they are prominent candidates for TeV gamma-ray sources. Our results
demonstrate that the analysis of positional correlations is a powerful approach
indispensable in cases when low statistics limits or even prohibits the
standard case-by-case identification.Comment: 5 pages, MNRAS styl
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