1,126 research outputs found
Dark matter component decaying after recombination: lensing constraints with Planck data
It has been recently suggested~\cite{Berezhiani:2015yta} that emerging
tension between cosmological parameter values derived in high-redshift (CMB
anisotropy) and low-redshift (cluster counts, Hubble constant) measurements can
be reconciled in a model which contains subdominant fraction of dark matter
decaying after recombination. We check the model against the CMB Planck data.
We find that lensing of the CMB anisotropies by the large-scale structure gives
strong extra constraints on this model, limiting the fraction as at
2\, confidence level. However, investigating the combined data set of
CMB and conflicting low- measurements, we obtain that the model with
\% exhibits better fit (by 1.5-3\, depending on the
lensing priors) compared to that of the concordance CDM cosmological
model.Comment: 5 pages, 4 figures; v2: journal version, pages++, figures+
Dark matter and generation of galactic magnetic fields
A new scenario for creation of galactic magnetic fields is proposed which is
operative at the cosmological epoch of the galaxy formation, and which relies
on unconventional properties of dark matter. Namely, it requires existence of
feeble but long range interaction between the dark matter particles and
electrons. In particular, millicharged dark matter particles or mirror
particles with the photon kinetic mixing to the usual photon can be considered.
We show that in rotating protogalaxies circular electric currents can be
generated by the interactions of free electrons with dark matter particles in
the halo, while the impact of such interactions on galactic protons is
considerably weaker. The induced currents may be strong enough to create the
observed magnetic fields on the galaxy scales with the help of moderate dynamo
amplification. In addition, the angular momentum transfer from the rotating gas
to dark matter component could change the dark matter profile and formation of
cusps at galactic centers would be inhibited. The global motion of the ionized
gas could produce sufficiently large magnetic fields also in filaments and
galaxy clusters.Comment: 8 pages, refined version published in Eur. Phys. J. C73, 2620 (2013
No evidence for gamma-ray halos around active galactic nuclei resulting from intergalactic magnetic fields
We analyze the gamma-ray halo around stacked AGNs reported in Ap.J.Lett.,
2010, 722, L39. First, we show that the angular distribution of gamma-rays
around the stacked AGNs is consistent with the angular distribution of the
gamma-rays around the Crab pulsar, which is a point source for Fermi/LAT. This
makes it unlikely that the halo is caused by an electromagnetic cascade of TeV
photons in the intergalactic space. We then compare the angular distribution of
gamma-rays around the stacked AGNs with the point-spread function (PSF) of
Fermi/LAT and confirm the existence of an excess above the PSF. However, we
demonstrate that the magnitude and the angular size of this effect is different
for photons converted in the front and back parts of the Fermi/LAT instrument,
and thus is an instrumental effect.Comment: accepted to A&
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