Black holes with masses between a million and a billion solar masses are seen in the centres of many galaxies, even at high redshift. Their origin remains unknown and hard to explain, raising the possibility that these black holes are primordial rather than astrophysical. I will discuss the motivation for this scenario and the difficulty in finding a working model, especially due to...
I review the observational evidence for primordial black holes from a variety of lensing, dynamical, accretion and gravitational-wave effects. As I will show, all of these (over 20) may be explained by a single and simple unified model, naturally shaped by the thermal history of the Universe. In the second part of my talk, I will comment on the novel feature of vorticity in black holes, which...
Partially due to the detection of gravitational waves LIGO, Virgo and KAGRA (LVK), there has been renewed interest in the possibility that primordial black holes (PBHs) make up all, or a fraction of, dark matter. However, the origin of the LVK black holes is still not well understood. To explore the possibility that (at least some) of the LVK black holes are primordial in nature requires an...
I will discuss the interplay between the phenomenology of primordial black holes and the dark matter searches. I will focus on how a sub-dominant component of PBHs interacts with the bulk of the DM. In particular, I will describe how a DM “mini-halo” is expected to form around PBHs, with relevant phenomenological consequences. The focus will be on two relevant effects. (i) If the bulk of the...
The FINUDA magnet for Light Axion SearcH (FLASH) is a large resonant cavity haloscope planned to probe new physics as part of the INFN Frascati National Laboratories near Rome (Italy). The frequency range accessible overlaps with the Very High Frequency (VHF) range of the radio wave spectrum and allows for a search in high frequency gravitational waves (HFGW) in the frequency range (100–300)...
Gravitational microlensing is known as a productive method for exoplanet discovery and characterisation, and crucially, it also provides an experimental avenue to constrain the galactic PBH abundance in the mass regime from ~ 10−12 M⊙ (i.e. asteroid-mass scale) to ∼ 1000 M⊙. The key to probing the very lowest masses is fast cadence observations on the order of hours to minutes. We previously...
This talk examines the cosmic microwave background (CMB) bounds on solar mass and heavier primordial black holes (PBHs). While the CMB bound is often regarded as the most stringent in this mass regime, its computation relies on several astrophysical assumptions, including accretion geometry, dark matter halo formation, and the treatment of energy injection and deposition. By applying realistic...
If primordial black holes (PBHs) constitute the dark matter (DM), stars forming in dark-matter dominated environments with low velocity dispersions, such as ultra-faint dwarf galaxies, may capture a black hole at birth. The capture probability is non-negligible for PBHs of masses around $10^{20}$g, and increases with stellar mass. Moreover, infected stars are turned into virtually invisible...
Cosmology textbooks typically assume that the early universe was dominated by relativistic particles. But if even a relatively small number of black holes were created after inflation, they would have constituted an increasingly large fraction of the total energy density as the universe expanded. I’ll argue that it is well-motivated to scenarios in which the early universe included an era in...
We present a new general paradigm for the production of dark matter (DM) relic abundance, regurgitated DM, based on the evaporation of early Universe primordial black holes (PBHs) themselves formed from DM particles. We discuss a minimal realization of the model with dark sector in which a first-order phase transition results in the formation of Fermiball remnants that collapse to PBHs, which...
We explore the possibility of dynamically producing the observed matter-antimatter asymmetry of the Universe entirely from the evaporation of primordial black holes (PBH), that are formed in an inflaton-dominated
background. Considering the inflaton $(\phi)$ to oscillate in a monomial
potential $V(\phi)\propto\phi^n$, we show that it is possible to obtain
the desired baryon asymmetry via...
The parameter spaces of leptogenesis and ultralight ($M_{\rm PBH} \leq 10^9$g) Primordial Black Holes (PBHs) are notoriously difficult to constrain, but while experiments struggle to probe sterile neutrino masses heavier than a few GeV, the new window into the early universe opened by Gravitational Wave (GW) astronomy offers realistic hopes of detecting GW signals associated with PBHs. Since...
PBHs may have formed from a sufficiently large amplitude of perturbation in the early Universe. The central aim of the formation studies is to predict the abundance and other properties of PBHs for a given cosmological scenario. Both numerical relativity simulations and analytical investigations play important roles. In this talk I will introduce some of the recent developments, focusing on...
I will present the first non-perturbative study of a single-field model of inflation with a localized departure from slow-roll. Using lattice simulations, we find that small-scale oscillatory features in the potential can lead to drastic changes in the evolution of the inflationary Universe, with profound phenomenological implications. In certain cases, the entire Universe gets trapped in an...
Primordial black holes can arise from quantum fluctuations produced during cosmic inflation. Stochastic inflation is a method to compute the fluctuation statistics non-perturbatively, including non-Gaussianities. I discuss recent progress in the numerical implementation of the method, allowing us to compute the radial dependence of the fluctuations' compaction function in random patches of...
We propose an inflation scenario with three independent stages of cold, warm and thermal inflation, respectively, driven by different scalar fields, motivated by the large number of such fields predicted by most extensions of the Standard Model. We show, in particular, that the intermediate period of warm inflation naturally leads to large density fluctuations on small scales, which can lead...
A viable model of large-field (chaotic) inflation with efficient production of primordial black holes is proposed in Starobinsky-like (modified) supergravity leading to the ”no-scale-type” Kähler potential and the Wess-Zumino-type (”renormalizable”) superpotential. The cosmological tilts are in good (within 1$\sigma$) agreement with Planck measurements of the cosmic microwave background...
I will overview the current status of observational constraints on the abundance of Primordial Black Holes (PBHs) of all masses, including astrophysical uncertainties on stellar microlensing constraints, constraints on (more realistic) extended mass functions, and prospects for probing asteroid mass PBHs.
The current merger rate prescriptions for primordial black holes (PBHs) only apply to peaked mass distributions. For an extended mass distribution that includes features from the QCD epoch, additional effects must be taken into account that can importantly change these rates. Based on new estimations of the merger rates of early and late PBH binaries, I will present an update of the status...
Primordial black holes (PBHs) may contribute to the observed abundance of dark matter. We use the black-hole mass distribution obtained from the detected binary black hole merger events by the LIGO/VIRGO gravitational-wave observatories, with a signal to noise ratio (SNR) $>$ 8. We search for and place limits on PBHs in the stellar-mass range. We also simulate binary black holes following...
During the talk, I will delve into the unique candidate of Planck mass Primordial Black Hole (PBH) relics as dark matter. These relics, arising from the evaporation of light PBHs with initial masses ranging from 1g to approximately 10^6g, possess the potential to account for the entirety of dark matter in our universe. My presentation will encompass a thorough review of existing constraints on...
After many years where the belief that dark matter is in the form of elementary particles has been the dominant paradigm, there is now growing support for the idea that at least in part dark matter is made up of primordial black holes. Although there have been a number of observational and theoretical pointers in this direction, there are two areas where a strong case has been made that...
Primordial black holes (PBHs) remain a viable dark matter candidate in the asteroid-mass range. I will show that, if PBHs lie within this mass range and make up most or all of the dark matter, the PBH abundance would be large enough for at least one object to cross through the inner Solar System per decade. Since Solar System ephemerides are modeled and measured to extremely high precision,...
Asteroid mass primordial black holes (mass $10^{16}-10^{21}$ grams) are viable candidates to describe the total dark matter content of the universe. One of the interesting features of these primordial black holes (PBHs) being a source of dark matter is their Hawking temperature is greater than 100 keV, meaning that charged particle pairs can easily be created for nontrivial hawking radiation...
In this analysis, we investigate the scenario wherein Primordial Black Holes (PBHs) with very low masses ($ M_{\rm PBH} \lesssim 10^9{\rm\,g} $) undergo evaporation during the Big Bang Nucleosynthesis (BBN) epoch. This evaporation process leads to a non-standard behavior in the expansion rate of the Universe, which plays a crucial role in determining the freeze-out of nuclear reactions. This...
The energy injection through Hawking evaporation has been used to put strong constraints on primordial black holes as a dark
matter candidate at masses below 1e18 g. However, recent work has shown that Hawking’s semiclassical approximation breaks
down at latest after half-decay. Beyond this point, the evaporation could be significantly suppressed. In this work, we review
existing...
Among many mechanisms that produce particles via gravitational interactions, the production of particles from the expansion of the universe represents a simple and irreducible source of particles from the early universe, that can account for the present abundance of dark matter. Another feasible and interesting mechanism is to have a population of primordial black holes that, through...
One of the main difficulties in scenarios involving primordial black holes (PBHs) are the rather special conditions required to produce them, typically demanding major tunings in the inflationary potential or very specific conditions following phase transitions. Some authors have found a promising alternative in the preheating epoch, just after inflation, when metric feedback would resonantly...
When investigating primordial black hole (PBH) formation scenarios, a central question is to characterise their initial clustering, which then determines their subsequent clustering evolution throughout cosmic history. In this talk I will present how top compute PBH clustering in the presence of non-perturbative non-Gaussianities, making use of the stochastic- $\delta N$ formalism. To this...
I examine one-loop corrections from small-scale curvature perturbations to the superhorizon-limit ones in single-field inflation models, which have recently caused controversy. I consider the case where the Universe experiences transitions of slow-roll (SR) → intermediate period → SR. The intermediate period can be an ultra-slow-roll period or a resonant amplification period, either of which...
The non-Gaussian tail of the PDF of primordial scalar perturbations is a key element to determine the abundance of primordial black holes. These primordial non-Gaussianities arise, at least partly, from the non-linear, super-horizon dynamics of inflationary perturbations. Such non-linear evolution is usually addressed through the stochastic $\delta N$ formalism. This formalism is based on the...
Accurately predicting primordial black hole (PBH) formation in the early universe requires a knowledge of the full probability distribution function of curvature perturbations. This is typically obtained by employing the $\delta N$ formalism, a powerful non-perturbative technique which identifies the curvature perturbation with the difference in amounts of logarithmic expansion between...
In the string axiverse scenario, primordial black holes (PBHs) can sustain non-negligible spin parameters as they evaporate. We show that tracking both the mass and spin evolution of a PBH in its final hour can yield a purely gravitational probe of new physics beyond the TeV scale, allowing one to determine the number of new scalars, fermions, vector bosons, and spin-3/2 particles....
Primordial Black Holes (PBHs) could play a relevant role in several physical phenomena. They are particularly attractive as a candidate for dark matter, seeds of supermassive black holes, sources of gravitational waves, etc. In addition, the observation of an evaporating black hole would provide definitive information on the elementary particles present in nature, including new degrees of...
We discuss a novel mechanism for producing topologically stable monopoles (TSMs) from the quantum mechanical decay of metastable cosmic strings in the early universe. For a dimensionless string tension parameter $G\mu \approx 10^{-9} - 10^{-5}$, the monopoles are superheavy with masses of order $10^{15} - 10^{17}$ GeV. The stochastic gravitational wave emission arises from metastable strings...
We propose methods to determine the mass and spin of PBHs based on measuring specific features of the primary emitted Hawking spectra. In the previous edition of this conference, we focused on masses between 5 × 10^7 and 10^12 kg and adimensional spin parameter a = 0.1–0.5. Now we extend those ranges in distant independent ways.
We investigate values of a ≳ 0.6, measuring the energy and...
In this talk, I will discuss possible probes of Heavy Neutral Leptons (HNLs) with Primordial Black Holes (PBHs).
If produced in the early Universe with an initial mass of ∼ $10^{15}$ g, PBHs are expected to evaporate at the present time producing sizable
fluxes of particles in their last instants. These “exploding” black holes will emit bursts of
Standard Model particles as well as new...
The Domain Wall (DW) problem is the fact that DW networks that result from the spontaneous breaking of discrete symmetries tend to dominate the universe's energy budget.
However, if the symmetry is not exact the network annihilates and the problem turns into a virtue, as the network tends to be an abundant component before its collapse, and is thus easier to probe.
In this talk, I will...
Ultra-light PBHs with masses $M<5\times 10^8\mathrm{g}$ can dominate transiently the energy budget of the Universe and reheat the Universe through their evaporation taking place before Big Bang Nucleosynthesis (BBN). Interestingly enough, the inhomogeneous distribution of a population of such light PBHs can induce the abundant production of GWs due to second-order gravitational effects. In...
The recent data releases by multiple pulsar timing array (PTA) experiments show evidence for Hellings-Downs angular correlations indicating that the observed stochastic common spectrum can be interpreted as a stochastic gravitational wave background. We study whether the signal may originate from gravitational waves induced by high-amplitude primordial curvature perturbations. Such large...
Primordial black holes (PBHs) could have been formed in the very early Universe from large amplitude perturbations of the metric. Their formation is naturally enhanced during phase-transitions, because of the softening of the equation of state, from the electron weak transition, corresponding to PBHs as CDM candidate, till the Nucleosynthesis, when the PBHs formed could be the seeds of SMBHs....
Primordial black holes (PBHs) may form in the early universe, and could have relevance to cosmic evolution, particularly as a dark matter candidate. Forming PBHs requires increased power on small scales, corresponding to some kind of feature in the inflaton potential. I will present a study of the fine-tuning of PBH formation for four representative inflation models, discussing the different...
GWs induced by primordial fluctuations can be affected by the modification of the sound speed $c^2_s$ and the equation of state parameter $w$ once the curvature fluctuations reenter the cosmological horizon. That softening can also significantly boost the production of PBHs at the mass scale where the softening arises. In this work, we consider a hypothetical softening of $w$ and $c^2_s$...
It has been understood for a long time that the reduction in the equation of state during a phase transition in the Early Universe leads to an exponential enhancement in the formation rate of PBHs. However, this exponential sensitivity to the EoS (via the collapse threshold) is the same sensitivity that PBH formation shows to the amplitude of the primordial power spectrum. In this talk I will...
We introduce a novel mechanism for making primordial black hole (PBH) dark matter from the mergers of unstable PBH progenitors.
Since PBH redshift like non-relativistic matter, they can
dominate the energy density of the early universe even if produced with only a tiny initial abundance. Once established, this era of black hole domination (BHD) is only empirically viable if PBH evaporates...
Very little is known about the universe's history from after the end of inflation until the Big Bang nucleosynthesis (BBN), which spans more than $10^{39}$ orders of magnitude in time scales. In this work, we show that if there was a long period of matter domination (at least $10^8$ scale factors) in this unknown period, and if the particle causing the matter domination has self-interactions,...
We perform the numerical simulation of primordial black hole formation from a nonspherical profile of the initial curvature perturbation $\zeta$. We consider the background expanding universe filled with the perfect fluid with the linear equation of state $p=w\rho$ ($w=1/3$ or $1/5$), where $p$ and $\rho$ are the pressure and the energy density, respectively. The initial condition is set in a...
In empty Minkowski space, the CP-violating electroweak θ-term can be rotated away by the redefinition of quark and lepton states by anomalous B+L phase transformations. I will argue this is no longer true in black hole spacetime, where non-zero θ-term remains on the black hole horizon. This boundary term acts as a source of CP-asymmetric Hawking radiation. The phenomenon may be responsible for...
We look into whether the spherical collapse model is a good approximation in a numerical relativity cosmological simulation and describe the spacetime’s evolution during nonlinear collapse. In the simulation, we evolve a quasi-spherical structure, where fully nonlinear initial conditions are provided by perturbing the ΛCDM model with the comoving curvature perturbation, defined as a 3D...
Vorticity has recently been suggested to be a property of highly-spinning black holes. The connection between vorticity and limiting spin represents a universal feature shared by objects of maximal microstate entropy, so-called saturons. Using Q-ball-like saturons as a laboratory for black holes, we study the collision of two such objects and find that vorticity can have a large impact on the...
Observations of gravitational waves (GW) from mergers of binary black holes has opened up a new door into cosmology. Due to their weak interaction with matter, we hope to observe Primordial GWs among the various signals that are expected from current and future-generation detectors. This offers a new and exciting opportunity to explore the physics of the early Universe. Quantum vacuum...
We simulated the formation of spinning and non-spinning PBH from the collapse of superhorizon density fluctuations using full numerical relativity in the case of the approximately matter dominated case. We showed that there are two formation mechanism (1) direct collapse where the perturbation itself forms a BH and (2) accretion collapse where the perturbation generate a potential well which...
The transition epoch between the end of inflation and the beginning of thermal radiation domination, known as ‘reheating’, remains as one of the fundamental open problems in Cosmology. During the earliest stages of reheating, the oscillating inflaton condensate is supposed to decay non-perturbatively (via parametric resonance) into other lighter bosonic degrees of freedom that are coupled to...
We consider primordial black holes formation from adiabatic cosmological perturbation of the Early Universe dominated by a massless scalar field. These are sourced by a time independent curvature profile imposed on super horizon scale, corresponding to pure growing modes of the scalar field. Assuming spherical symmetry we study the collapse of these cosmological perturbations using the...
Phase transitions can have a dramatic impact on physics in the early universe. We illustrate this by discussing a novel mechanism of dark matter production and a related novel mechanism of primordial black hole production, both of which hinge on cosmological phase transitions.
I will first discuss why the excess radio background measured by the balloon borne experiments ARCADE 2 is a mystery and might be an indication of new physics. After having reviewed a few solutions that have been proposed and that are now ruled out I will focus on the possibility that the excess is explained by radiative decays of relic neutrinos, showing how they produce a very nice fit to...
This presentation introduces a cosmological mechanism featuring a spectator field and investigates its connection to the formation of primordial black holes (PBHs) and dark matter. By considering fluctuations during inflation, we study a natural PBH formation process that doesn’t rely on exotic physics in the potential and the fine-tuning issue can be avoided. Observational constraints...
A possible way to generate primordial black holes as candidates for the entirety of dark matter is a large power spectrum of inflationary curvature fluctuations. Recently, questions have been raised regarding the validity of perturbation theory in this context. We compute the one-loop power spectrum in ultra-slow roll inflation, including all relevant interactions for such analysis, along with...
We investigate the formation of primordial black holes (PBHs) during the inflation by nucleation of supercritical bubbles in a multiverse scenario. We find that when the inflaton slowly passes by a neighboring vacuum, the nucleating rate of supercritical bubbles would inevitably attain a peak, so the mass distribution of multiverse PBHs, and the mass of peak can be up to $10^{18}M_\odot$. We...
