106 research outputs found
Stochastic gravitational-wave background at 3G detectors as a smoking gun for microscopic dark matter relics
No full textMicroscopic horizonless relics could form in the early universe either directly through gravitational collapse or as stable remnants of the Hawking evaporation of primordial black holes. In both cases they completely or partially evade cosmological constraints arising from Hawking evaporation and in certain mass ranges can explain the entirety of the dark matter. We systematically explore the stochastic gravitational-wave background associated with the formation of microscopic dark-matter relics in various scenarios, adopting an agnostic approach and discussing the limitations introduced by existing constraints, possible ways to circumvent the latter, and expected astrophysical foregrounds. Interestingly, this signal is at most marginally detectable with current interferometers but could be detectable by third-generations instruments such as the Einstein Telescope, strengthening their potential as discovery machines
Primordial black hole dark matter from inflation: The reverse engineering approach
No full textConstraining the inflationary epoch is one of the aims of modern cosmology. In order to fully exploit current and future small-scale observations, it is necessary to devise tools to directly relate them to the early Universe's dynamics. We present here a novel reverse engineering approach able to connect fundamental late-time observables to consistent inflationary dynamics and, eventually, to the inflaton potential. Employing this procedure, we are able to describe which conditions can give rise to a raised plateau in the power spectrum of curvature perturbations at small scales, which are not constrained by CMB observations. Within this new phenomenologically driven approach, we find that inflation can generate a raised plateau in the spectrum of curvature perturbations that potentially connects three fundamental observables; a dominant component of the dark matter in the form of asteroid-mass/atomic-size primordial black holes, detectable signals in stochastic gravitational waves, and a subdominant fraction of stellar-mass primordial black holes mergers
Searching for mass-spin correlations in the population of gravitational-wave events: the GWTC-3 case study
No full textOne fundamental goal of the newly born gravitational wave astronomy is
discovering the origin of the observed binary black hole mergers. Towards this
end, identifying features in the growing wealth of data may help in
distinguishing different formation pathways. While large uncertainties still
affect the binary formation models, spin-mass relations remain characteristic
features of specific classes of channels. By focusing on the effective inspiral
spin , the best reconstructed spin-related merger parameter,
we show that current GWTC-3 data support the hypothesis that a fraction of
events may display mass-spin correlations similar to one expected by dynamical
formation channels of either astrophysical or primordial nature. We quantify
the Bayesian evidence in favour of those models, which are substantially
preferred when compared to the Gaussian phenomenological model adopted to
describe the distribution of in the recent LIGO/Virgo/KAGRA
population analyses.Comment: 6+7 pages, 6 figures. v2: matching published versio
High-redshift JWST Observations and Primordial Non-Gaussianity
No full textSeveral bright and massive galaxy candidates at high redshifts have been
recently observed by the James Webb Space Telescope. Such early massive
galaxies seem difficult to reconcile with standard Cold Dark Matter
model predictions. We discuss under which circumstances such observed massive
galaxy candidates can be explained by introducing primordial non-Gaussianity in
the initial conditions of the cosmological perturbations.Comment: 10 pages, 4 figures. v2: matching published versio
Hunt for light primordial black hole dark matter with ultrahigh-frequency gravitational waves
No full textLight primordial black holes may comprise a dominant fraction of the dark matter in our Universe. This paper critically assesses whether planned and future gravitational wave detectors in the ultrahigh-frequency band could constrain the fraction of dark matter composed of subsolar primordial black holes. Adopting the state-of-the-art description of primordial black hole merger rates, we compare various signals with currently operating and planned detectors. As already noted in the literature, our findings confirm that detecting individual primordial black hole mergers with currently existing and operating proposals remains difficult. Current proposals involving gravitational wave to electromagnetic wave conversion in a static magnetic field and microwave cavities feature a technology gap with respect to the loudest gravitational wave signals from primordial black holes of various orders of magnitude. However, we point out that one recent proposal involving resonant LC circuits represents the best option in terms of individual merger detection prospects in the range (1-100) MHz. In the same frequency range, we note that alternative setups involving resonant cavities, whose concept is currently under development, might represent a promising technology to detect individual merger events. We also show that a detection of the stochastic gravitational wave background produced by unresolved binaries is possible only if the theoretical sensitivity of the proposed Gaussian beam detector is achieved. Such a detector, whose feasibility is subject to various caveats, may be able to rule out some scenarios for asteroidal mass primordial black hole dark matter. We conclude that pursuing dedicated studies and developments of gravitational wave detectors in the ultrahigh-frequency band remains motivated and may lead to novel probes on the existence of light primordial black holes
Can we identify primordial black holes? Tidal tests for subsolar-mass gravitational-wave observations
No full textThe detection of a subsolar object in a compact binary merger is regarded as one of the smoking gun
signatures of a population of primordial black holes (PBHs). We critically assess whether these systems
could be distinguished from stellar binaries, for example composed of white dwarfs or neutron stars, which
could also populate the subsolar mass range. At variance with PBHs, the gravitational-wave signal from
stellar binaries is affected by tidal effects, which dramatically grow for moderately compact stars as those
expected in the subsolar range. We forecast the capability of constraining tidal effects of putative subsolar
neutron star binaries with current and future LIGO-Virgo-KAGRA (LVK) sensitivities as well as nextgeneration experiments. We show that, should LVK O4 run observe subsolar neutron-star mergers, it could
measure the (large) tidal effects with high significance. In particular, for subsolar neutron-star binaries, O4
and O5 projected sensitivities would allow measuring the effect of tidal disruption on the waveform in a
large portion of the parameter space, also constraining the tidal deformability at Oð10%Þ level, thus
excluding a primordial origin of the binary. Vice versa, for subsolar PBH binaries, model-agnostic upper
bounds on the tidal deformability can rule out neutron stars or more exotic competitors. Assuming events
similar to the subthreshold candidate SSM200308 reported in LVK O3b data are PBH binaries, O4
projected sensitivity would allow ruling out the presence of neutron-star tidal effects at ≈3σ CL, thus
strengthening the PBH hypothesis. Future experiments would lead to even stronger (> 5σ) conclusions on
potential discoveries of this kind
Lensing constraints on ultradense dark matter halos
No full textCosmological observations precisely measure primordial variations in the
density of the Universe at megaparsec and larger scales, but much smaller
scales remain poorly constrained. However, sufficiently large initial
perturbations at small scales can lead to an abundance of ultradense dark
matter minihalos that form during the radiation epoch and survive into the
late-time Universe. Because of their early formation, these objects can be
compact enough to produce detectable microlensing signatures. We investigate
whether the EROS, OGLE, and HSC surveys can probe these halos by fully
accounting for finite source size and extended lens effects. We find that
current data may already constrain the amplitudes of primordial curvature
perturbations in a new region of parameter space, but this conclusion is
strongly sensitive to yet undetermined details about the internal structures of
these ultradense halos. Under optimistic assumptions, current and future HSC
data would constrain a power spectrum that features an enhancement at scales , and an amplitude as low as may be accessible. This is a particularly interesting regime because
it connects to primordial black hole formation in a portion of the
LIGO/Virgo/Kagra mass range and the production of scalar-induced gravitational
waves in the nanohertz frequency range reachable by pulsar timing arrays. These
prospects motivate further study of the ultradense halo formation scenario to
clarify their internal structures.Comment: 17 pages, 10 figures. v2: matching published versio
From inflation to black hole mergers and back again: Gravitational-wave data-driven constraints on inflationary scenarios with a first-principle model of primordial black holes across the QCD epoch
No full textRecent population studies have searched for a subpopulation of primordial black holes (PBHs) in the gravitational-wave (GW) events so far detected by LIGO/Virgo/KAGRA (LVK), in most cases adopting a phenomenological PBH mass distribution. When deriving such a population from first principles in the standard scenario, however, the equation of state of the Universe at the time of PBH formation may strongly affect the PBH abundance and mass distribution, which ultimately depend on the power spectrum of cosmological perturbations. Here we improve on previous population studies on several aspects: (i) we adopt state-of-the-art PBH formation models describing the collapse of cosmological perturbations across the QCD epoch; (ii) we perform the first Bayesian multipopulation inference on GW data including PBHs and directly using power spectrum parameters instead of phenomenological distributions; (iii) we critically confront the PBH scenario with LVK phenomenological models describing the GWTC-3 catalog both in the neutron-star and in the BH mass ranges, also considering PBHs as a subpopulation of the total events. Our results confirm that LVK observations prevent the majority of the dark matter to be in the form of stellar mass PBHs. We find that the best-fit PBH model can comprise a small fraction of the total events, in particular it can naturally explain events in the mass gaps. If the lower mass-gap event GW190814 is interpreted as a PBH binary, we predict that LVK should detect up to a few subsolar mergers and one to approximate to 30 lower mass-gap events during the upcoming O4 and O5 runs. Finally, mapping back the best-fit power spectrum into an ultra-slow-roll inflationary scenario, we show that the latter predicts detectable PBH mergers in the LVK band, a stochastic GW background detectable by current and future instruments, and may include the entirety of dark matter in asteroid-mass PBHs
The recent gravitational wave observation by pulsar timing arrays and primordial black holes: the importance of non-gaussianities
No full textWe study whether the signal seen by pulsar timing arrays (PTAs) may originate
from gravitational waves (GWs) induced by large primordial perturbations. Such
perturbations may be accompanied by a sizeable primordial black hole (PBH)
abundance. We improve existing analyses and show that PBH overproduction
disfavors Gaussian scenarios for scalar-induced GWs at 2{\sigma} and
single-field inflationary scenarios, accounting for non-Gaussianity, at
3{\sigma} as the explanation of the most constraining NANOGrav 15-year data.
This tension can be relaxed in models where non-Gaussianites suppress the PBH
abundance. On the flip side, the PTA data does not constrain the abundance of
PBHs.Comment: V3: Version published on PRL. 15 pages and 8 figures. Full article +
supplementary materials. V1 appeared on Thu, 29 Jun 202
Ruling out Initially Clustered Primordial Black Holes as Dark Matter
No full textCombining constraints from microlensing and Lyman- forest, we provide
a simple argument to show that large spatial clustering of stellar-mass
primordial black holes at the time of formation, such as the one induced by the
presence of large non-Gaussianities, is ruled out. Therefore, it is not
possible to evade existing constraints preventing stellar-mass primordial black
holes to be a dominant constituent of the dark matter by boosting their initial
clustering.Comment: 5 pages + supplementary material. 2 figures. v2: matching version
published in PR
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