5,554 research outputs found
Detecting the gravitational wave background from primordial black hole dark matter
The black hole merging rates inferred after the gravitational-wave detection
by Advanced LIGO/VIRGO and the relatively high mass of the progenitors are
consistent with models of dark matter made of massive primordial black holes
(PBH). PBH binaries emit gravitational waves in a broad range of frequencies
that will be probed by future space interferometers (LISA) and pulsar timing
arrays (PTA). The amplitude of the stochastic gravitational-wave background
expected for PBH dark matter is calculated taking into account various effects
such as initial eccentricity of binaries, PBH velocities, mass distribution and
clustering. It allows a detection by the LISA space interferometer, and
possibly by the PTA of the SKA radio-telescope. Interestingly, one can
distinguish this background from the one of non-primordial massive binaries
through a specific frequency dependence, resulting from the maximal impact
parameter of binaries formed by PBH capture, depending on the PBH velocity
distribution and their clustering properties. Moreover, we find that the
gravitational wave spectrum is boosted by the width of PBH mass distribution,
compared with that of the monochromatic spectrum. The current PTA constraints
already rule out broad-mass PBH models covering more than three decades of
masses, but evading the microlensing and CMB constraints due to clustering.Comment: 12 pages, 4 figure
Cosmic troublemakers: the Cold Spot, the Eridanus Supervoid, and the Great Walls
The alignment of the CMB Cold Spot and the Eridanus supervoid suggests a
physical connection between these two relatively rare objects. We use galaxy
cata\-logues with photometric (2MPZ) and spectroscopic (6dF) redshift
measurements, supplemented by low-redshift compilations of cosmic voids, in
order to improve the 3D mapping of the matter density in the Eridanus
constellation. We find evidence for a supervoid with a significant elongation
in the line-of-sight, effectively spanning the total redshift range .
Our tomographic imaging reveals important substructure in the Eridanus
supervoid, with a potential interpretation of a long, fully connected system of
voids. We improve the analysis by extending the line-of-sight measurements into
the antipodal direction that interestingly crosses the Northern Local Supervoid
at the lowest redshifts. Then it intersects very rich superclusters like
Hercules and Corona Borealis, in the region of the Coma and Sloan Great Walls,
as a possible compensation for the large-scale matter deficit of Eridanus. We
find that large-scale structure measurements are consistent with a central
matter underdensity , projected transverse radius
Mpc/h with an extra deepening in the centre, and
line-of-sight radius Mpc/h, i.e. an ellipsoidal
supervoid. The expected integrated Sachs-Wolfe imprint of such an elongated
supervoid is at the level, thus
inappropriate to accounting for the Cold Spot pattern in the CMB.Comment: 13 pages, 9 figures. Accepted by MNRAS in this for
Massive Primordial Black Holes from Hybrid Inflation as Dark Matter and the seeds of Galaxies
In this paper we present a new scenario where massive Primordial Black Holes
(PBH) are produced from the collapse of large curvature perturbations generated
during a mild waterfall phase of hybrid inflation. We determine the values of
the inflaton potential parameters leading to a PBH mass spectrum peaking on
planetary-like masses at matter-radiation equality and producing abundances
comparable to those of Dark Matter today, while the matter power spectrum on
scales probed by CMB anisotropies agrees with Planck data. These PBH could have
acquired large stellar masses today, via merging, and the model passes both the
constraints from CMB distortions and micro-lensing. This scenario is supported
by Chandra observations of numerous BH candidates in the central region of
Andromeda. Moreover, the tail of the PBH mass distribution could be responsible
for the seeds of supermassive black holes at the center of galaxies, as well as
for ultra-luminous X-rays sources. We find that our effective hybrid potential
can originate e.g. from D-term inflation with a Fayet-Iliopoulos term of the
order of the Planck scale but sub-planckian values of the inflaton field.
Finally, we discuss the implications of quantum diffusion at the instability
point of the potential, able to generate a swiss-cheese like structure of the
Universe, eventually leading to apparent accelerated cosmic expansion.Comment: 17 pages, 5 figures, comments welcom
Quantum diffusion beyond slow-roll: implications for primordial black-hole production
Primordial black-holes (PBH) can be produced in single-field models of
inflation with a quasi-inflection point in the potential. In these models, a
large production of PBHs requires a deviation from the slow-roll (SR)
trajectory. In turn, this SR violation can produce an exponential growth of
quantum fluctuations. We study the back-reaction of these quantum modes on the
inflationary dynamics using stochastic inflation in the Hamilton-Jacobi
formalism. We develop a methodology to solve quantum diffusion beyond SR in
terms of the statistical moments of the probability distribution. We apply
these techniques to a toy model potential with a quasi-inflection point. We
find that there is an enhancement of the power spectrum due to the dominance of
the stochastic noise in the phase beyond SR. Moreover, non-Gaussian corrections
become as well relevant with a large positive kurtosis. Altogether, this
produces a significant boost of PBH production. We discuss how our results
extend to other single-field models with similar dynamics. We conclude that the
abundance of PBHs in this class of models should be revisited including quantum
diffusion.Comment: 17+7 pages, 5 figures. Matches JCAP versio
Reconstruction of the null-test for the matter density perturbations
We systematically study the null-test for the growth rate data first
presented in [S. Nesseris and D. Sapone, arXiv:1409.3697] and we reconstruct it
using various combinations of data sets, such as the and or
Type Ia supernovae (SnIa) data. We perform the reconstruction in two different
ways, either by directly binning the data or by fitting various dark energy
models. We also examine how well the null-test can be reconstructed by future
data by creating mock catalogs based on the cosmological constant model, a
model with strong dark energy perturbations, the and models, and
the large void LTB model that exhibit different evolution of the matter
perturbations. We find that with future data similar to an LSST-like survey,
the null-test will be able to successfully discriminate between these different
cases at the level.Comment: 15 pages; 10 figures; 5 table
Primordial black holes from the QCD epoch: Linking dark matter, baryogenesis and anthropic selection
If primordial black holes (PBHs) formed at the quark-hadron epoch, their mass
must be close to the Chandrasekhar limit, this also being the characteristic
mass of stars. If they provide the dark matter (DM), the collapse fraction must
be of order the cosmological baryon-to-photon ratio , which
suggests a scenario in which a baryon asymmetry is produced efficiently in the
outgoing shock around each PBH and then propagates to the rest of the Universe.
We suggest that the temperature increase in the shock provides the ingredients
for hot spot electroweak baryogenesis. This also explains why baryons and DM
have comparable densities, the precise ratio depending on the size of the PBH
relative to the cosmological horizon at formation. The observed value of the
collapse fraction and baryon asymmetry depends on the amplitude of the
curvature fluctuations which generate the PBHs and may be explained by an
anthropic selection effect associated with the existence of galaxies. We
propose a scenario in which the quantum fluctuations of a light stochastic
spectator field during inflation generate large curvature fluctuations in some
regions, with the stochasticity of this field providing the basis for the
required selection. Finally, we identify several observational predictions of
our scenario that should be testable within the next few years. In particular,
the PBH mass function could extend to sufficiently high masses to explain the
black hole coalescences observed by LIGO/Virgo.Comment: 37 pages, 3 figures, published in MNRA
Pair Creation of Dilaton Black Holes in Extended Inflation
Dilatonic Charged Nariai instantons mediate the nucleation of black hole
pairs during extended chaotic inflation. Depending on the dilaton and inflaton
fields, the black holes are described by one of two approximations in the
Lorentzian regime. For each case we find Euclidean solutions that satisfy the
no boundary proposal. The complex initial values of the dilaton and inflaton
are determined, and the pair creation rate is calculated from the Euclidean
action. Similar to standard inflation, black holes are abundantly produced near
the Planck boundary, but highly suppressed later on. An unusual feature we find
is that the earlier in inflation that the dilatonic black holes are created,
the more highly charged they can be.Comment: 23 pages, LaTeX, 6 figures; submitted to Phys. Rev.
Detecting the Stochastic Gravitational Wave Background from Primordial Black Hole Formation
Primordial Black Holes (PBH) from peaks in the curvature power spectrum could
constitute today an important fraction of the Dark Matter in the Universe. At
horizon reentry, during the radiation era, order one fluctuations collapse
gravitationally to form black holes and, at the same time, generate a
stochastic background of gravitational waves coming from second order
anisotropic stresses in matter. We study the amplitude and shape of this
background for several phenomenological models of the curvature power spectrum
that can be embedded in waterfall hybrid inflation, axion, domain wall, and
boosts of PBH formation at the QCD transition. For a broad peak or a nearly
scale invariant spectrum, this stochastic background is generically enhanced by
about one order of magnitude, compared to a sharp feature. As a result,
stellar-mass PBH from Gaussian fluctuations with a wide mass distribution are
already in strong tension with the limits from Pulsar Timing Arrays, if they
constitute a non negligible fraction of the Dark Matter. But this result is
mitigated by the uncertainties on the curvature threshold leading to PBH
formation. LISA will have the sensitivity to detect or rule out light PBH down
to . Upcoming runs of LIGO/Virgo and future interferometers
such as the Einstein Telescope will increase the frequency lever arm to
constrain PBH from the QCD transition. Ultimately, the future SKA Pulsar Timing
Arrays could probe the existence of even a single stellar-mass PBH in our
Observable Universe.Comment: 20 pages, 5 figures, comments welcom
Simulations of Cold Electroweak Baryogenesis
We present real-time lattice simulations of Cold Electroweak Baryogenesis, in
which the baryon asymmetry of the Universe is generated during tachyonic
electroweak symmetry breaking at the end of inflation. In the minimal
realisation of the model, only three parameters remain undetermined: the
strength of CP-violation, the Higgs mass and the speed of the symmetry breaking
quench. The dependence of the asymmetry on these parameters is studied.Comment: 4 pages. Presented at International Conference on Strong and
Electroweak Matter (SEWM 2006), Upton, New York, 10-13 May 200
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