123 research outputs found
Gamma Ray Astronomy with Magnetized Zevatrons
Nearby sources of cosmic rays up to a ZeV(=10^21 eV) could be observed with a
multi-messenger approach including secondary gamma-rays and neutrinos. If
cosmic rays above ~10^18 eV are produced in magnetized environments such as
galaxy clusters, the flux of secondary gamma-rays below ~1 TeV can be enhanced
up to several orders of magnitudes compared to unmagnetized sources. A
particular source of enhancement are synchrotron and cascade photons from
e^+e^- pairs produced by protons from sources with relatively steep injection
spectra proportional to E^-2.6. Such sources should be visible at the same time
in ultra-high energy cosmic ray experiments and gamma-ray telescopes.Comment: 4 pages, 3 ps figure
Axion driven cosmic magneto-genesis during the QCD crossover
We propose a mechanism for the generation of a magnetic field in the early
universe during the QCD crossover assuming that dark matter is made of axions.
Thermoelectric fields arise at pressure gradients in the primordial plasma due
to the difference in charge, energy density and equation of state between the
quark and lepton components. The axion field is coupled to the EM field, so
when its spatial gradient is misaligned with the thermoelectric field, an
electric current is driven. Due to the finite resistivity of the plasma an
electric field appears that is generally rotational. For a QCD axion mass
consistent with observational constraints and a conventional efficiency for
turbulent dynamo amplification --- driven by the same pressure gradients
responsible for the thermoelectric fields --- a magnetic field is generated on
subhorizon scales. After significant Alfv\'enic unwinding it reaches a present
day strength of G on a characteristic scale 20
pc. The resulting combination of is significantly stronger than in
any astrophysical scenario, providing a clear test for the cosmological origin
of the field through -ray observations of distant blazars. The
amplitude of the pressure gradients may be inferred from the detection of
concomitant gravitational waves, while several experiments are underway to
confirm or rule out the existence of axions.Comment: Published in PR
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