2 research outputs found
Overcoming the Back Reaction on Turbulent Motions in the Presence of Magnetic Fields
Standard magnetohydrodynamic theories, such as the mean field dynamo theory,
have been criticized when the back reaction of the magnetic field on turbulent
motions is neglected. For the dynamo, this back reaction has been argued to
suppress the turbulent motions required for optimal mean field production. Here
it is suggested that if the magnetic field is spatially intermittent, for
example residing in flux tubes, the back reaction on turbulent flows may be
significantly reduced.Comment: Accepted to Physical Review Letters, 15 pages, plain Te
Ultra-high energy cosmic rays without GZK cutoff
We study the decays of ultraheavy (m_X \geq 10^{13}GeV) and quasistable
(lifetime \tau_X much larger than the age of the Universe t_0) particles as the
source of Ultra High Energy Cosmic Rays (UHE CR). These particles are assumed
to constitute a tiny fraction \xi_X of CDM in the Universe, with \xi_X being
the same in the halo of our Galaxy and in the intergalactic space. The
elementary-particle and cosmological scenarios for these particles are briefly
outlined. The UHE CR fluxes produced at the decays of X- particles are
calculated. The dominant contribution is given by fluxes of photons and
nucleons from the halo of our Galaxy and thus they do not exibit the GZK
cutoff. The extragalactic components of UHE CR are suppressed by the smaller
extragalactic density of X-particles and hence the cascade limit is relaxed. We
discuss the spectrum of produced Extensive Air Showers (EAS) and a signal from
Virgo cluster as signatures of this model.Comment: Revtex, 5 pages, 1 ps-figur