Primordial Black Hole Dark Matter Research Articles

Primordial black holes as a dark matter candidate - a brief overview

Historically the most popular dark matter candidates have been new elementary particles, such as Weakly Interacting Massive Particles and axions. However Primordial Black Holes (PBHs), black holes formed from overdensities in the early Universe, are another possibility. The discovery of gravitational waves from mergers of tens of Solar mass black hole binaries by LIGO-Virgo has generated a surge in interest in PBH dark matter. We overview the formation of PBHs, observational probes of their abundance, and some of the key open questions in the field.

Gravitation wave signal from asteroid mass primordial black hole dark matter

Gravitation wave signal from asteroid mass primordial black hole dark matter

Limits on the primordial black holes dark matter with future MeV detectors

Limits on the primordial black holes dark matter with future MeV detectors

Primordial black holes dark matter and secondary gravitational waves from warm Higgs-G inflation

We explore the role of dissipative effects during warm inflation leading to the small-scale enhancement of the power spectrum of curvature perturbations. In this paper, we specifically focus on non-canonical warm inflationary scenarios and study a model of warm Higgs-G inflation, in which the Standard Model Higgs boson drives inflation, with a Galileon-like non-linear kinetic term. We show that in the Galileon-dominated regime, the primordial power spectrum is strongly enhanced, leading to the formation of primordial black holes (PBH) with a wide range of the mass spectrum. Interestingly, PBHs in the asteroid mass window ∼ (1017–1023) g are generated in this model, which can explain the total abundance of dark matter in the Universe. In our analysis, we also calculate the secondary gravitational waves (GW) sourced by these small-scale overdense fluctuations and find that the induced GW spectrum can be detected in future GW detectors, such as LISA, BBO, DECIGO, etc. Our scenario thus provides a novel way of generating PBHs as dark matter and a detectable stochastic GW background from warm inflation. We also show that our scenario is consistent with the swampland and the trans-Planckian censorship conjectures and, thus, remains in the viable landscape of UV complete theories.

Testing Primordial Black Hole Dark Matter with Atacama Large Millimeter Array Observations of the Gravitational Lens B1422+231

We examine the flux density ratio anomaly in the quadruply imaged strong gravitational lens, B1422+231, and consider the contribution of 10–103M⊙ primordial black holes (PBHs) as a potential dark matter constituent. We describe the first flux density ratio measurement of B1422+231 in the millimeter-wave band using the Atacama Large Millimeter Array (ALMA). The flux density of the quasar at 233 GHz is dominated by synchrotron emission and the source size is estimated to be less than 66.9 pc. The observed flux density ratios at 233 GHz are similar to those measured in other wave bands, which cannot be explained by a simple smooth mass model of the lens galaxy. We examine the probability of the flux density ratio anomaly arising from PBH microlensing using ray tracing simulations. The simulations consider the cases where 10% and 50% of dark matter are 10–103M⊙ PBHs with a power law mass function. The simulated scenarios are consistent with the ALMA observations, so PBH dark matter cannot be ruled out as a cause of flux density ratio anomalies. Our analysis shows that the anomalous flux density ratio for B1422+231 can be explained by a lens model with a significant fraction of dark matter being PBHs. This study demonstrates the potential for new constraints on PBH dark matter using ALMA observations of multiply imaged strong gravitational lenses.

Search for scalar induced gravitational waves in the international pulsar timing array data release 2 and NANOgrav 12.5 years datasets

We perform a Bayesian search in the latest Pulsar Timing Array (PTA) datasets for a stochastic gravitational wave (GW) background sourced by curvature perturbations at scales 10^5105 Mpc^{-1}\lesssim−1≲ k\lesssim 10^8≲108 Mpc^{-1}−1. These re-enter the Hubble horizon at temperatures around and below the QCD crossover phase transition in the early Universe. We include a stochastic background of astrophysical origin in our search and properly account for constraints on the curvature power spectrum from the overproduction of primordial black holes (PBHs). We find that the International PTA Data Release 2 significantly favors the astrophysical model for its reported common-spectrum process, over the curvature-induced background. On the other hand, the two interpretations fit the NANOgrav 12.5 years dataset equally well. We then set new upper limits on the amplitude of the curvature power spectrum at small scales. These are independent from, and competitive with, indirect astrophysical bounds from the abundance of PBH dark matter. Upcoming PTA data releases will provide the strongest probe of the curvature power spectrum around the QCD epoch.

Planck constraints and gravitational wave forecasts for primordial black hole dark matter seeded by multifield inflation

Planck constraints and gravitational wave forecasts for primordial black hole dark matter seeded by multifield inflation

Signatures of primordial black holes in gravitational wave clustering

The possible existence of primordial black holes (PBHs) is an open question in modern cosmology. Among the probes to test it, gravitational waves (GW) coming from their mergers constitute a powerful tool. In this work, we study how stellar mass PBH binaries could affect measurements of the clustering of merger events in future GW surveys. We account for PBH binaries formed both in the early and late Universe and show that the power spectrum modification they introduce can be detected at ∼ 2σ-3σ (depending on some assumptions) whenever PBH mergers make up at least ∼ 60% of the overall number of detected events. By adding cross-correlations with galaxy surveys, this threshold is lowered to ∼ 40%. In the case of a poor redshift determination of GW sources, constraints are degraded by about a factor of 2. Assuming a theoretical model for the PBH merger rate, we can convert our results to constraints on the fraction of dark matter in PBHs, f PBH. Finally, we perform a Bayesian model selection forecast and confirm that the analysis we develop could be able to detect ∼30 M ⊙ PBHs if they account for f PBH ∼ 10-4 – 10-3, depending on the model uncertainty considered, being thus competitive with other probes.

Modelling uncertainties in wide binary constraints on primordial black holes

ABSTRACT Dark matter in the form of compact objects with mass Mco ≳ 10 M⊙ can be constrained by its dynamical effects on wide binary stars. Motivated by the recent interest in primordial black hole dark matter, we revisit the theoretical modelling involved in these constraints. We improve on previous studies in several ways. Specifically, we (i) implement a physically motivated model for the initial wide-binary semimajor axis distribution, (ii) include unbound binaries, and (iii) take into account the uncertainty in the relationship between semimajor axis and observed angular separation. These effects all tend to increase the predicted number of wide binaries (for a given compact object population). Therefore, the constraints on the halo fraction in compact objects, fco, are significantly weakened. For the wide binary sample used in the most recent calculation of the constraints, we find the fraction of halo dark matter in compact objects is fco < 1 for $M_{\rm co} \approx 300 \, \mathrm{ M}_{\odot }$, tightening with increasing Mco to fco < 0.26 for $M_{\rm co} \gtrsim 1000 \, \mathrm{ M}_{\odot }$.

Primordial black hole dark matter from catastrogenesis with unstable pseudo-Goldstone bosons

We propose a new scenario for the formation of asteroid-mass primordial black holes (PBHs). Our mechanism is based on the annihilation of the string-wall network associated with the breaking of a U(1) global symmetry into a discrete ZN symmetry. If the potential has multiple local minima (N > 1) the network is stable, and the annihilation is guaranteed by a bias among the different vacua. The collapse of the string-wall network is accompanied by catastrogenesis, a large production of pseudo-Goldstone bosons (pGBs) — e.g. axions, ALPs, or majorons — gravitational waves, and PBHs. If pGBs rapidly decay into products that thermalize, as predicted e.g. in the high-quality QCD axion and heavy majoron models, they do not contribute to the dark matter population, but we show that PBHs can constitute 100% of the dark matter. The gravitational wave background produced by catastrogenesis with heavy unstable axions, ALPs, or majorons could be visible in future interferometers.

Astrometric microlensing of primordial black holes with Gaia

The Gaia space telescope allows for unprecedented accuracy for astrometric measurements of stars in the Galaxy. In this work, we explore the sensitivity of Gaia to detect primordial black hole (PBH) dark matter through the distortions that PBHs would create in the apparent trajectories of background stars, an effect known as astrometric microlensing (AML). We present a novel calculation of the lensing probability, and we combine this with the existing publicly released Gaia eDR3 stellar catalog to predict the expected rate of AML events that Gaia will see. We also compute the expected distribution of a few event observables, which will be useful for reducing backgrounds.Assuming that the astrophysical background rate of AML like events due to other sources is negligible, we then compute the potential exclusion that could be set on the parameter space of PBHs with a monochromatic mass function. We find that Gaia is sensitive to PBHs in the range of 0.4 M ⊙–5 × 107 M ⊙, and has peak sensitivity to PBHs of ∼ 10 M ⊙ for which it can rule out as little as a fraction 3 × 10-4 of dark matter composed of PBHs. With this exquisite sensitivity, Gaia has the potential to rule out a PBH origin for the gravitational wave signals seen at LIGO/Virgo. Our novel calculation of the lensing probability includes for the first time, the effect of intermediate duration lensing events, where the lensing event lasts for a few years, but for a period which is still shorter than the Gaia mission lifetime. The lower end of our predicted mass exclusion is especially sensitive to this class of lensing events. As and when time-series data for Gaia is released, and once we have a better understanding of the astrophysical background rate to AML signals, our prediction of the lensing rate and event observable distributions will be useful to estimate the true exclusion/discovery of the PBH parameter space utilizing this data.

Baryogenesis and primordial black hole dark matter from heavy metastable particles

We propose a novel and simple scenario to explain baryon asymmetry and dark matter (DM) by utilizing an early matter-dominated era (EMDE) caused by a heavy metastable particle. Within the EMDE, lack of pressure enhances the formation of primordial black holes (PBHs) which can then contribute to the relic abundance of DM. The eventual decay of heavy metastable particle that has baryon number and $CP$-violating interactions reheats the Universe and gives rise to baryon asymmetry. Since in this setup, PBH serves as a DM candidate, the particle physics model may not require new stable degrees of freedom which leads to more freedom in the model-building side. As an example, we show that a modulus field which dominates the energy density of the Universe prior to its decay, may explain both DM and baryon asymmetry in the Universe in the context of the minimally supersymmetric Standard Model while the lightest superparticle is not stable and cannot be a DM candidate due to the $R$-parity violating interactions needed for baryogenesis.

Superradiant axion clouds around asteroid-mass primordial black holes

We analyze the dynamics and observational signatures of axion clouds formed via the superradiant instability around primordial black holes, focusing on the mass range 1014 - 1018 kg where the latter may account for all the dark matter.We take into account the leading effects of axion self-interactions, showing that, even though these limit the number of axions produced within each cloud,a large number of superradiant axions become free of the black hole's gravitational potential and accumulate in the intergalactic medium or even in the host galaxy, depending on their escape velocity. This means that primordial black hole dark matter may lead to a sizeable astrophysical population of non-relativistic axions, with masses ranging from 0.1 eV to 1 MeV, depending on the primordial black hole mass and spin.We then show that if such axions couple to photons their contribution to the galactic and extragalactic background flux, mainly in the X-ray and gamma-ray band of the spectrum, is already beyond current observational limits for a large range of parameters that are, therefore, excluded. We finish by showing the prospects of the Athena X-ray telescope to further probe this co-existence of primordial black holes and axions.

Search for the evaporation of primordial black holes with H.E.S.S.

Primordial Black Holes (PBHs) are hypothetical black holes predicted to have been formed from density fluctuations in the early Universe. PBHs with an initial mass around 1014–1015 g are expected to end their evaporation at present times in a burst of particles and very-high-energy (VHE) gamma rays. Those gamma rays may be detectable by the High Energy Stereoscopic System (H.E.S.S.), an array of imaging atmospheric Cherenkov telescopes. This paper reports on the search for evaporation bursts of VHE gamma rays with H.E.S.S., ranging from 10 to 120 seconds, as expected from the final stage of PBH evaporation and using a total of 4816 hours of observations. The most constraining upper limit on the burst rate of local PBHs is 2000 pc-3 yr-1 for a burst interval of 120 seconds, at the 95% confidence level. The implication of these measurements for PBH dark matter are also discussed.

Dark matter prospects with COSI: ALPs, PBHs and sub-GeV dark matter

We study the prospects in the search of dark matter offered by the newly selected NASA MeV mission COSI (Compton Spectrometer and Imager). This instrument is designed and optimized to detect spectral lines, and we show it offers an exquisite possibility to detect dark matter directly decaying or annihilating into monochromatic gamma-rays. This is the case, for example, for axion-like particles (ALPs) which undergo decay into two photons. Furthermore, we show that COSI can lead to important progress in the quest for primordial black holes (PBHs) dark matter, through measurements of the 511 keV line from the positrons produced via Hawking evaporation.We also outline opportunities for the search of continuum signals, such as those expected from sub-GeV dark matter annihilation/decay into leptons and PBH evaporation into photons. We find that also in this case COSI can lead to improvements of current bounds.

Extended primordial black hole mass functions with a spike

ABSTRACT We introduce a modification of the Press–Schechter formalism aimed to derive general mass functions for primordial black holes (PBHs). In this case, we start from primordial power spectra (PPS) which include a monochromatic spike, typical of ultra slow-roll inflation models. We consider the PBH formation as being associated to the amplitude of the spike on top of the linear energy density fluctuations coming from a PPS with a blue index. By modelling the spike with a lognormal function, we study the properties of the resulting mass function spikes, and compare these to the underlying extended mass distributions. When the spike is at PBH masses, which are much lower than the exponential cut-off of the extended distribution, very little mass density is held by the PBHs within the spike, and it is not ideal to apply the Press–Schechter formalism in this case as the resulting characteristic overdensity is too different from the threshold for collapse. It is more appropriate to do so when the spike mass is similar to, or larger than the cut-off mass. Additionally, it can hold a similar mass density as the extended part. Such particular mass functions also contain large numbers of small PBHs, especially if stable PBH relics are considered, and they can provide ${\sim}1000\, {\rm M}_\odot$ seeds for the supermassive black holes at the centres of present-day galaxies. The constraints on the fraction of dark matter in PBHs for monochromatic mass functions are somewhat relaxed when there is an additional underlying extended distribution of masses.

Primordial black holes and secondary gravitational waves produced by S-dual inflation model

<sec>It is discussed in this work to produce primordial black hole (PBH) dark matter (DM) and scalar induced secondary gravitational waves by using the enhancement mechanism with a peak function in the non-canonical kinetic term in S-dual inflation. It is shown explicitly that the power spectrum for the primordial curvature perturbation can be enhanced at 10<sup>12</sup>, 10<sup>8</sup> and 10<sup>5</sup> Mpc<sup>–1</sup>, respectively, that the primordial black hole dark matter with peak mass around 10<sup>–13</sup> solar mass, the Earth’s mass and the stellar mass are generated, respectively, and that the scalar induced gravitational wave with peak frequency around mHz, μHz and nHz are created, respectively. The primordial black hole with the mass scale 10<sup>–13</sup> solar mass can make up almost all the dark matter and the associated scalar induced secondary gravitational waves is testable by spaced based gravitational wave observatory.</sec><sec>The amplitude of primordial curvature perturbations on a small scale can become large by the enhancement mechanism with a peak function in the non-canonical kinetic term. We apply the enhancement mechanism to S-dual inflation to produce abundant PBHs and observable scalar induced gravitational waves (SIGWs). The power spectrum on a large scale is consistent with observational constraint, and the power spectrum on a small scale is enhanced to the 0.01. It is possible that either sharp peak or broad peak possesses a different peak shape for the peak function by choosing a different value of <i>q</i>. By adjusting the peak position <i>ϕ</i><sub>p</sub> in the peak function, the power spectrum is enhanced on a different scale, henceforth associated with the generation of SIGWs with a different peak frequency, PBHs with different mass are produced. We choose three different values of <i>ϕ</i><sub>p</sub> to obtain enhance power spectrum at 10<sup>12</sup>, 10<sup>8</sup> and 10<sup>5</sup> Mpc<sup>–1</sup>, respectively. The enhanced curvature perturbation produces PBH DM with peak mass around 10<sup>–13</sup> solar mass, the Earth’s mass and the stellar mass, and SIGW with peak frequency around mHz, µHz and nHz, respectively. The stellar mass PBHs may explain black holes observed by LIGO/Virgo collaboration, and the earth-mass PBHs may explain the planet 9. The PBH with the mass scale 10<sup>–13</sup> solar mass can make up almost all the dark matter. The SIGW with the peak frequency around nHz is testable by pulsar timing array observations, and SIGW with the peak frequency around mHz is testable by space based GW observatory. The results show that the enhancement mechanism with a peak function in the non-canonical kinetic term works for S-dual inflation.</sec>

Primordial Black Holes as dark matter candidates: Constraints from the diffuse MeV emission

For more than 20 years, the Compton telescope had provided the best measurements of the Galactic diffuse MeV spectrum. Recently, our analysis of 16 years of data from the SPectrometer on INTEGRAL (SPI) measured this emission with a higher signal-to-noise ratio. At MeV energies, the dominant contribution to the diffuse emission comes from inverse Compton scattering. Nonetheless, sub-dominant emission from Primordial Black Hole (PBH) Dark Matter (DM) can be searched for in these data. Hypothetically formed from the collapse of over-densities before Big Bang nucleosynthesis, PBHs are interesting candidates for DM in the ΛCDM model of cosmology. PBHs of masses between 1016 and 1018 g, in the so-called asteroid mass range, are currently unconstrained and can saturate the DM cosmological abundance. MeV emission from PBH in this mass range is expected to come from PBH evaporation. We searched for the PBH signal with 16 years of SPI data, and demonstrated that PBHs cannot account for all the DM if their mass is smaller than 4 × 1017 g.

Primordial black hole dark matter from inflation: The reverse engineering approach

Constraining 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.

Search for primordial black hole dark matter with x-ray spectroscopic and imaging satellite experiments and prospects for future satellite missions

Ultra-light primordial black holes (PBHs) in the mass range of 10$^{16}$ - 10$^{22}$ g are allowed by current observations to constitute a significant fraction, if not all, of the dark matter in the Universe. In this work, we present limits on ultra-light, non-rotating PBHs which arise from the non-detection of the Hawking radiation signals from such objects in the keV-MeV energy band. Namely, we consider observations from the current-generation missions XMM-Newton and INTEGRAL/SPI and discuss the observational perspectives of the future missions Athena, eXTP, and THESEUS for PBH searches. Based on 3.4 Msec total exposure time XMM-Newton observations of Draco dwarf spheroidal galaxy, we conclude that PBH with masses $\lesssim 10^{16}$ g can not make all dark matter at 95% confidence level. Our ON-OFF-type analysis of $>100$ Msec of INTEGRAL/SPI data on the Milky Way halo puts significantly stronger constraints. Only $\lesssim 10$% dark matter can be presented by PBHs with masses $\lesssim 3\cdot 10^{16}$ g while the majority of dark matter can not be represented by PBHs lighter than $7\cdot 10^{16}$ g at 95% confidence level. We discuss the strong impact of systematic uncertainty related to the variations of instrumental and astrophysical INTEGRAL/SPI background on the derived results and estimate its level. We also show that future large-field-of-view missions such as THESEUS/X-GIS will be able to improve the constraints by a factor of 10-100 depending on the level of control under the systematics of these instruments.