2,504 research outputs found
Importance of axion-like particles for very-high-energy astrophysics
Several extensions of the Standard Model predict the existence of Axion-Like
Particles (ALPs), very light spin-zero bosons with a two-photon coupling. ALPs
can give rise to observable effects in very-high-energy astrophysics. Above
roughly 100 GeV the horizon of the observable Universe progressively shrinks as
the energy increases, due to scattering of beam photons off background photons
in the optical and infrared bands, which produces e+e- pairs. In the presence
of large-scale magnetic fields photons emitted by a blazar can oscillate into
ALPs on the way to us and back into photons before reaching the Earth. Since
ALPs do not interact with background photons, the effective mean free path of
beam photons increases, enhancing the photon survival probability. While the
absorption probability increases with energy, photon-ALP oscillations are
energy-independent, and so the survival probability increases with energy
compared to standard expectations. We have performed a systematic analysis of
this effect, interpreting the present data on very-high-energy photons from
blazars. Our predictions can be tested with presently operating Cherenkov
Telescopes like H.E.S.S., MAGIC, VERITAS and CANGAROO III as well as with
detectors like ARGO-YBJ and MILAGRO and with the planned Cherenkov Telescope
Array and the HAWC-ray observatory. ALPs with the right properties to produce
the above effects can possibly be discovered by the GammeV experiment at
FERMILAB and surely by the planned photon regeneration experiment ALPS at DESY.Comment: 4 pages, 5 figures. Proceeding of the workshop "TAUP2011", Munich 5 -
9 September 2011 (to appear in the Proceedings
Accurate Estimation of a Coil Magnetic Dipole Moment
In this paper, a technique for accurate estimation of the moment of magnetic
dipole is proposed. The achievable accuracy is investigated, as a function of
measurement noise affecting estimation of magnetic field cartesian components.
The proposed technique is validated both via simulations and experimentally.Comment: Preprin
Detection of distant AGN by MAGIC: the transparency of the Universe to high-energy photons
The recent detection of blazar 3C279 by MAGIC has confirmed previous
indications by H.E.S.S. that the Universe is more transparent to
very-high-energy gamma rays than previously thought. We show that this fact can
be reconciled with standard blazar emission models provided photon oscillations
into a veri light Axion-Like Particle occur in extragalactic magnetic fields. A
quantitative estimate of this effect explains the observed spectrum of 3C279.
Our prediction can be tested in the near future by the satellite-borne GLAST
detector as well as by the ground-based Imaging Atmospheric Cherenkov
Telescpoes H.E.S.S., MAGIC, CANGAROO III, VERITAS and by the Extensive Air
Shower arrays ARGO-YBJ and MILAGRO.Comment: 4 pages, 1 figure, Proceeding of the Conference "4th Patras Workshop
on Axions, WIMPs and WISPs
Transparency of the Universe to gamma rays
Using the most recent observational data concerning the Extragalactic
Background Light and the Radio Background, for a source at a redshift z_s < 3
we compute the energy E_0 of an observed gamma-ray photon in the range 10 GeV <
E_0 < 10^13 GeV such that the resulting optical depth tau_gamma(E_0,z_s) takes
the values 1, 2, 3 and 4.6, corresponding to an observed flux dimming of e^-1 =
0.37, e^-2 = 0.14, e^-3 = 0.05 and e^-4.6 = 0.01, respectively. Below a source
distance D = 8 kpc we find that tau_gamma(E_0,DH_0/c) < 1 for any value of E_0.
In the limiting case of a local Universe (z_s = 0) we compare our result with
the one derived in 1997 by Coppi and Aharonian. The present achievement is of
paramount relevance for the planned ground-based detectors like CTA, HAWC and
HiSCORE.Comment: 5 pages, 2 figures, MNRAS (2013) - in Pres
Evidence for an axion-like particle from blazar spectra?
Observations with the Imaging Atmospheric Cherenkov Telescopes H.E.S.S.,
MAGIC, CANGAROO III and VERITAS have shown that the Universe is more
transparent than expected to gamma rays above 100GeV. As a natural explanation,
the DARMA scenario has previously been proposed, wherein photons can oscillate
into a new very light axionlike particle and vice-versa in the presence of
cosmic magnetic fields. Here we demonstrate that the most recent observations
further support the DARMA scenario, thereby making the existence of a very
light axion-like particle more likely.Comment: 4 pages, 1 figure. Proceeding of the "6th Patras Workshop on Axions,
WIMPs and WISPs", Zurich, Switzerland, 5 - 9 July 2010 (to appear in the
Proceedings
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