20 research outputs found
Dense DM clumps seeded by cosmic string loops and DM annihilation
We develop a model of production of the very dense clumps of DM in RD epoch
due to the accretion of DM on the loops of cosmic strings as the seeds. At some
time the loops disappear, for example due to the gravitational radiation, and
the remaining dense clumps produce the enhancement of the annihilation signal.
We take into account the velocity distribution of the strings, and consider the
two extreme regimes of DM annihilation: fast decay and continuous evaporation.
The produced annihilation flux of gamma radiation is detectable, and for some
parameters of DM particles and the strings can exceed the extragalactic flux of
the gamma-radiation observed by Fermi. For the fixed parameters of DM particles
(e.g. neutralino with fixed masses and cross-section of annihilation) one can
obtain the limits on the basic string parameter, tension \mu, which is stronger
than (more general) limits obtained from WMAP observations, cosmological
nucleosynthesis and gravitational lensing. In particular for the neutralino
with 100 GeV mass we exclude the interval
5\times10^{-10}<G{\mu}/c^2<5.1\times10^{-9}.Comment: 11 pages, 2 figures, published versio
Running Spectral Index and Formation of Primordial Black Hole in Single Field Inflation Models
A broad range of single field models of inflation are analyzed in light of
all relevant recent cosmological data, checking whether they can lead to the
formation of long-lived Primordial Black Holes (PBHs). To that end we calculate
the spectral index of the power spectrum of primordial perturbations as well as
its first and second derivatives. PBH formation is possible only if the
spectral index increases significantly at small scales, i.e. large wave number
. Since current data indicate that the first derivative of the
spectral index is negative at the pivot scale , PBH formation
is only possible in the presence of a sizable and positive second derivative
("running of the running") . Among the three small-field and five
large-field models we analyze, only one small-field model, the "running mass"
model, allows PBH formation, for a narrow range of parameters. We also note
that none of the models we analyze can accord for a large and negative value of
, which is weakly preferred by current data.Comment: 26 pages, 5 figures, Refs. added, Minor textual change; version to
appear in JCA
Active Galactic Nuclei at the Crossroads of Astrophysics
Over the last five decades, AGN studies have produced a number of spectacular
examples of synergies and multifaceted approaches in astrophysics. The field of
AGN research now spans the entire spectral range and covers more than twelve
orders of magnitude in the spatial and temporal domains. The next generation of
astrophysical facilities will open up new possibilities for AGN studies,
especially in the areas of high-resolution and high-fidelity imaging and
spectroscopy of nuclear regions in the X-ray, optical, and radio bands. These
studies will address in detail a number of critical issues in AGN research such
as processes in the immediate vicinity of supermassive black holes, physical
conditions of broad-line and narrow-line regions, formation and evolution of
accretion disks and relativistic outflows, and the connection between nuclear
activity and galaxy evolution.Comment: 16 pages, 5 figures; review contribution; "Exploring the Cosmic
Frontier: Astrophysical Instruments for the 21st Century", ESO Astrophysical
Symposia Serie