31,732 research outputs found
Ultrahigh Energy Cosmic Ray Nuclei from Extragalactic Pulsars and the effect of their Galactic counterparts
The acceleration of ultrahigh energy nuclei in fast spinning newborn pulsars
can explain the observed spectrum of ultrahigh energy cosmic rays and the trend
towards heavier nuclei for energies above eV as reported by the
Auger Observatory. Pulsar acceleration implies a hard injection spectrum () due to pulsar spin down and a maximum energy eV due to the limit on the spin rate of neutron stars. We have
previously shown that the escape through the young supernova remnant softens
the spectrum, decreases slightly the maximum energy, and generates secondary
nuclei. Here we show that the distribution of pulsar birth periods and the
effect of propagation in the interstellar and intergalactic media modifies the
combined spectrum of all pulsars. By assuming a normal distribution of pulsar
birth periods centered at 300 ms, we show that the contribution of
extragalactic pulsar births to the ultrahigh energy cosmic ray spectrum
naturally gives rise to a contribution to very high energy cosmic rays (VHECRs,
between and eV) by Galactic pulsar births. The required
injected composition to fit the observed spectrum depends on the absolute
energy scale, which is uncertain, differing between Auger Observatory and
Telescope Array. The contribution of Galactic pulsar births can also bridge the
gap between predictions for cosmic ray acceleration in supernova remnants and
the observed spectrum just below the ankle, depending on the composition of the
cosmic rays that escape the supernova remnant and the diffusion behavior of
VHECRs in the Galaxy.Comment: 21 pages, 5 figure, JCAP submitte
Scattering of plasmons at the intersection of two metallic nanotubes: Implications for tunnelling
We study theoretically the plasmon scattering at the intersection of two
metallic carbon nanotubes. We demonstrate that for a small angle of crossing,
, the transmission coefficient is an oscillatory function of
, where is the interaction parameter of the Luttinger
liquid in an individual nanotube. We calculate the tunnel density of states,
, as a function of energy, , and distance, , from the
intersection. In contrast to a single nanotube, we find that, in the geometry
of crossed nanotubes, conventional "rapid" oscillations in due
to the plasmon scattering acquire an aperiodic "slow-breathing" envelope which
has nodes.Comment: 4 pages, 2 figures (revised version
IceCube Constraints on Fast-Spinning Pulsars as High-Energy Neutrino Sources
Relativistic winds of fast-spinning pulsars have been proposed as a potential
site for cosmic-ray acceleration from very high energies (VHE) to ultrahigh
energies (UHE). We re-examine conditions for high-energy neutrino production,
considering the interaction of accelerated particles with baryons of the
expanding supernova ejecta and the radiation fields in the wind nebula. We make
use of the current IceCube sensitivity in diffusive high-energy neutrino
background, in order to constrain the parameter space of the most extreme
neutron stars as sources of VHE and UHE cosmic rays. We demonstrate that the
current non-observation of eV neutrinos put stringent constraints on
the pulsar scenario. For a given model, birthrates, ejecta mass and
acceleration efficiency of the magnetar sources can be constrained. When we
assume a proton cosmic ray composition and spherical supernovae ejecta, we find
that the IceCube limits almost exclude their significant contribution to the
observed UHE cosmic-ray flux. Furthermore, we consider scenarios where a
fraction of cosmic rays can escape from jet-like structures piercing the
ejecta, without significant interactions. Such scenarios would enable the
production of UHE cosmic rays and help remove the tension between their EeV
neutrino production and the observational data.Comment: 23 pages, 8 figures; published in JCAP04(2016)01
Quantum Versus Jahn-Teller Orbital Physics in YVO and LaVO
We argue that the large Jahn-Teller (JT) distortions in YVO and LaVO
should suppress the quantum orbital fluctuation. The unusual magnetic
properties can be well explained based on LDA+ calculations using
experimental structures, in terms of the JT orbital. The observed splitting of
the spin-wave dispersions for YVO in C-type antiferromagnetic state is
attributed to the inequivalent VO layers in the crystal structure, instead
of the ``orbital Peierls state''. Alternative stacking of -plane exchange
couplings produces the c-axis spin-wave splitting, thus the spin system is
highly three dimensional rather than quasi-one-dimensional. Similar splitting
is also predicted for LaVO, although it is weak.Comment: 4 pages, 2 tables, 2 figures, (accepted by PRL
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