20 research outputs found
Adiabatic contraction revisited: implications for primordial black holes
We simulate the adiabatic contraction of a dark matter (DM) distribution
during the process of the star formation, paying particular attention to the
phase space distribution of the DM particles after the contraction. Assuming
the initial uniform density and Maxwellian distribution of DM velocities, we
find that the number of DM particles within the radius scales like
, leading to the DM density profile , in agreement with the Liouville theorem and previous numerical
studies. At the same time, the number of DM particles with periastra
smaller than is parametrically larger, , implying that
many particles contributing at any given moment into the density at
small have very elongated orbits and spend most of their time at distances
larger than . This has implications for the capture of DM by stars in the
process of their formation. As a concrete example we consider the case of
primordial black holes (PBH). We show that accounting for very eccentric orbits
boosts the amount of captured PBH by a factor of up to depending
on the PBH mass, improving correspondingly the previously derived constraints
on the PBH abundance.Comment: 8 pages, 3 figures, discussions added to the "Simulation of DM
orbits" part, fig.3 with several DM densities. Revised version to match
published versio
Possibility of hypothetical stable micro black hole production at future 100 TeV collider
We study the phenomenology of TeV-scale black holes predicted in theories
with large extra dimensions, under the further assumption that they are
absolutely stable. Our goal is to present an exhaustive analysis of safety of
the proposed 100 TeV collider, as it was done in the case of the LHC. We
consider the theories with different number of extra dimensions and identify
those for which a possible accretion to macroscopic size would have timescales
shorter than the lifetime of the Solar system. We calculate the cross sections
of the black hole production at the proposed 100 TeV collider, the fraction of
the black holes trapped inside the Earth and the resulting rate of capture
inside the Earth via an improved method. We study the astrophysical
consequences of stable micro black holes existence, in particular its influence
on the stability of white dwarfs and neutron stars. We obtain constraints for
the previously unexplored range of higher-dimensional Planck mass values.
Several astrophysical scenarios of the micro black hole production, which were
not considered before, are taken into account. Finally, using the astrophysical
constraints we consider the implications for future 100 TeV terrestrial
experiments. We exclude the possibility of the charged stable micro black holes
production.Comment: 11 pages, 8 figures, accepted for publication in EPJ
Constraints on primordial black holes as dark matter candidates from capture by neutron stars
We investigate constraints on primordial black holes (PBHs) as dark matter
candidates that arise from their capture by neutron stars (NSs). If a PBH is
captured by a NS, the star is accreted onto the PBH and gets destroyed in a
very short time. Thus, mere observations of NSs put limits on the abundance of
PBHs. High DM densities and low velocities are required to constrain the
fraction of PBHs in DM. Such conditions may be realized in the cores of
globular clusters if the latter are of a primordial origin. Assuming that cores
of globular clusters possess the DM densities exceeding several hundred
GeV/cm would imply that PBHs are excluded as comprising all of the dark
matter in the mass range . At the DM density of GeV/cm that has been
found in simulations in the corresponding models, less than 5% of the DM may
consist of PBH for these PBH masses.Comment: 7 pages, 2 figures, precise computation of dynamical friction added,
accepted for publication in PR
New limits on extragalactic magnetic fields from rotation measures
We take advantage of the wealth of rotation measures data contained in the
NRAO VLA Sky Survey catalogue to derive new, statistically robust, upper limits
on the strength of extragalactic magnetic fields. We simulate the extragalactic
magnetic field contribution to the rotation measures for a given field strength
and correlation length, by assuming that the electron density follows the
distribution of Lyman- clouds. Based on the observation that rotation
measures from distant radio sources do not exhibit any trend with redshift,
while the extragalactic contribution instead grows with distance, we constrain
fields with Jeans' length coherence length to be below 1.7~nG at the
level, and fields coherent across the entire observable Universe below 0.65~nG.
These limits do not depend on the particular origin of these cosmological
fields.Comment: 5 pages, 3 figures -- v2 to match PRL versio
Constraints on the massive graviton dark matter from pulsar timing and precision astrometry
The effect of a narrow-band isotropic stochastic GW background on pulsar
timing and astrometric measurements is studied. Such a background appears in
some theories of gravity. We show that the existing millisecond pulsar timing
accuracy () strongly constrains possible observational
consequences of theory of massive gravity with spontaneous Lorentz braking
\cite{dtt:2005}, essentially ruling out significant contribution of massive
gravitons to the local dark halo density. The present-day accuracy of
astrometrical measurements () sets less stringent
constraints on this theory.Comment: 4 pages, 1 figure; changes in content, references added, accepted for
publication in PR