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Black Holes in the Early Universe
Abstract
The existence of galaxies today implies that the early Universe must have been inhomogeneous. Some regions might have got
so compressed that they underwent gravitational collapse to produce black holes. Once formed, black holes in the early Universe
would grow by accreting nearby matter. A first estimate suggests that they might grow at the same rate as the Universe during
the radiation era and be of the order of 1015 to 1017 solar masses now. The observational evidence however is against the existence of such giant black holes. This motivates a
more detailed study of the rate of accretion which shows that black holes will not in fact substantially increase their original
mass by accretion. There could thus be primordial black holes around now with masses from 10−5 g upwards.
... The density distribution around a PBH could be accurately calculated through numerical hydrodynamic simulations similar to the simulations of PBH formation [31][32][33][34]. However, if the phenomena are considered not in the immediate vicinity of the PBH formation time but some time after, when the wave processes will damp out, then the approximation of quasi-stationary accretion can be used [35,36]. ...
... where the profiles obtained in Section 3 by taking into account the early annihilation in the central part considered in Section 4 are used as the density profile in the spike ρ(r). Thus, starting from a radius of ∼ 3r g , we assume that ρ(r) ∼ ρ max = 10 −14 g cm −3 , while at large radii, when the densities in Fig. 3 decrease to ρ max , the profiles shown in Fig. 3 are used under the integral in (31). After the beginning of the dust-like stage of the Universe at t > t eq , a DM halo begins to grow around the PBH at distances r > r infl (t eq ) through the mechanism of secondary accretion [25]. ...
... The density (32) does not exceed the halo density at r = r infl (t eq ). Therefore, the outer halo (32) makes a minor contribution to (31), while the central region of the halo with density (30) and the parts of the halo adjacent to it shown in Fig. 3 make a major contribution. ...
We show that density spikes begin to form from dark matter particles around primordial black holes immediately after their formation at the radiation-dominated cosmological stage. This follows from the fact that in the thermal velocity distribution of particles there are particles with low velocities that remain in finite orbits around black holes and are not involved in the cosmological expansion. The accumulation of such particles near black holes gives rise to density spikes. These spikes are considerably denser than those that are formed later by the mechanism of secondary accretion. The density spikes must be bright gamma-ray sources. Comparison of the calculated signal from particle annihilation with the Fermi-LAT data constrains the present-day cosmological density parameter for primordial black holes with masses from above by values from to , depending on . These constraints are several orders of magnitude more stringent than other known constraints.
... However, it has been realized that dark matter might also exist, possibly partly, in the form of macroscopic objects. Two of those, primordial black holes (PBHs) [1,2] and ultracompact minihalos (UCMHs) [3], will be discussed in greater detail below. 1 On the particle side, amongst many variants of what the dark matter could be, one quite promising possibility is that of so-called sterile neutrinos (see Ref. [6] for an early discussion on their role as dark-matter components and Refs. [7][8][9][10] for more recent reviews on their role in cosmology and astrophysics in general). ...
... [4,5]). 2 Increasing the number of sterile neutrinos, the number of model parameters raises significantly, and hence, the constraints on those become weaker. In view of the possibility to serve as a solution to possible small-scale issues of the standard model of cosmology (such as the so-called missing-satellite [11] or the too-Combining the two scenarios mentioned above, i.e. particle and macroscopic dark matter, to one consisting of sterile neutrinos aggregated to compact massive structures-either in the form of dark-matter halos around PBHs or in the form of UCMHs-is very tempting. ...
... These are black holes which have been produced in the very early Universe. Ever since PBHs were first postulated, they have received considerable attention [1,2]. The interest in them constituting (parts of) the dark matter [17] has been revived recently [14,[18][19][20][21][22][23][24], in particular through the gravitational-wave discovery of blackhole binary mergers [25,26]. ...
We investigate compact halos of sterile-neutrino dark matter and examine observable signatures with respect to neutrino and photon emission. Primarily, we consider two cases: primordial black-hole halos and ultra-compact mini-halos. In both cases, we find that there exists a broad range of possible parameter choices such that detection in the near future with X-ray and gamma-ray telescopes might be well possible. In fact, for energies above , the neutrino telescope IceCube would be a splendid detection machine for such macroscopic dark-matter candidates.
... These black holes have been termed primordial black holes (PBHs). The observational relevance of PBHs to cosmology has been established by the subsequent work of Carr and Hawking (1974) [3] and Carr (1975) [4]. See Refs. ...
... These black holes have been termed primordial black holes (PBHs). The observational relevance of PBHs to cosmology has been established by the subsequent work of Carr and Hawking (1974) [3] and Carr (1975) [4]. See Refs. ...
... The formation of PBHs through primordial fluctuations was initially proposed by Hawking (1971) [2] and Carr and Hawking (1974) [3] and further developed by Carr (1975) [4]. This formation mechanism has since been confirmed through numerical simulations based on numerical relativity, pioneered by Nadezhin, Novikov and Polnarev (1978) [7]. ...
Primordial black holes (PBHs) may have formed through the gravitational collapse of cosmological perturbations that were generated and stretched during the inflationary era, later entering the cosmological horizon during the decelerating phase, if their amplitudes were sufficiently large. In this review paper, we will briefly introduce the basic concept of PBHs and review the formation dynamics through this mechanism, the estimation of the initial spins of PBHs and the time evolution of type II fluctuations, with a focus on the radiation-dominated and (early) matter-dominated phases.
... After the first detection of gravitational wave which is directly emitted from a merger of a binary black hole (BH) by LIGO/Virgo collaboration [1], interests in primordial black holes (PBHs) [2,3] have been revived [4][5][6][7][8][9][10]. The masses of BHs to fit the merger rate distribute at around ∼ 30M , where M denotes the solar mass (= 2.0×10 33 g). ...
... For example, if the e-folding number of the first inflation with the running parameters is 30, a second inflation with 20 to 30 e-foldings is implicitly assumed. 3 The Planck 2018 (TT, TE, EE+lowE+lensing) constraints [72], which were released after the completion of this paper, are ns =0.9625 ± 0.0048, (6) αs =0.002 ± 0.010, ...
We study possibilities to explain the whole dark matter abundance by primordial black holes (PBHs) or to explain the merger rate of binary black holes estimated from the gravitational wave detections by LIGO/Virgo. We assume that the PBHs are originated in a radiation- or matter-dominated era from large primordial curvature perturbation generated by inflation. We take a simple model-independent approach considering inflation with large running spectral indices which are parametrized by , and consistent with the observational bounds. The merger rate is fitted by PBHs with masses of produced in the radiation-dominated era. Then the running of running should be , which can be tested by future observation. On the other hand, the whole abundance of dark matter is consistent with PBHs with masses of asteroids () produced in an early matter-dominated era if a set of running parameters are properly realized.
... The idea of PBHs was initially proposed in the 1960s by Zel'dovich and Novikov [1] and later refined by Hawking and Carr in the 1970s [2]. They suggested that PBHs could have emerged from dense regions in the early universe in a different way than the ones we typically see today, which are formed from collapsing massive stars. ...
... Numerous formation mechanisms for PBHs have been explored, including collapse from density fluctuations during different cosmic eras [2,[21][22][23][24][25], collapse in single and multi-field inflationary models [26][27][28][29][30][31][32][33][34][35][36][37], collapse of cosmic string loops [38,39], and collapse during a First Order Phase Transition (FOPT) [40][41][42][43][44][45][46][47][48][49][50][51][52]. Many of these processes have also been considered as potential sources of GWs [53][54][55][56][57][58][59][60][61][62][63][64]. ...
A bstract
We conduct an analysis of a U(1) B−L extended inert doublet model and obtained the parameter space allowing strong first order phase transitions. We show that a large part of the parameter space can cause double first-order phase transitions. Whereas both of these phase transitions can generate a detectable stochastic gravitational wave background, one of them can create primordial black holes with appreciable abundance. The primordial black holes generated at the high scale transition can account for the dark matter maintaining the correct relic abundance. We also show specific benchmark cases and their consequences from the aspect of primordial black holes and gravitational waves.
... This also clears the path for interesting small-scale phenomenology. For example, large scalar perturbations (or enhanced non-Gaussianity [3]) could lead to the production of primordial black holes (PBHs) [4], which might explain a fraction -if not the totality-of dark matter (see, e.g., the recent review [5]). Even in the absence of PBH formation, a large peak in the power spectrum would lead to enhanced gravitational waves (GWs) sourced at second order in perturbation theory [6,7]. ...
... A large peak in the primordial scalar power spectrum enhances the likeliness of large overdensities at horizon re-entry, and therefore can lead to primordial black hole (PBH) formation [4]. Since the probability of forming PBHs depends strongly on how likely large perturbations are, the precise calculation of the PBHs abundance is highly sensitive to the amplitude of the power spectrum, as well as to any non-Gaussian tail of the probability distribution function (PDF). ...
A plethora of inflationary models can produce interesting small-scale phenomenology, such as enhanced scalar fluctuations leading to primordial black hole (PBH) production and large scalar-induced GW. Nevertheless, good models must simultaneously explain current observations on all scales. In this work, we showcase our methodology to establish the small-scale phenomenology of inflationary models on firm grounds. We consider the case of hybrid -attractors, and focus on a reduced parameter space featuring the two potential parameters which roughly determine the position of the peak in the scalar power spectrum, , and its amplitude. We first constrain the parameter space by comparing the large-scale predictions for with current CMB anisotropies measurements and upper limits on -distortions. We take into account uncertainties due to the reheating phase, and observe that the parameter-space area compatible with large-scale constraints shrinks for extended reheating stages. We then move to smaller scales, where we find that non-Gaussianity at peak scales is of the local type and has amplitude . This ensures that non-linear effects are subdominant, motivating us to employ the tree-level to compute the abundance of PBHs and the spectrum of induced GWs for models consistent with large-scale tests. The former allows us to further constrain the parameter space, by excluding models which over-produce PBHs. We find that a subset of viable models can lead to significant production of PBHs, and a fraction of these is within reach for LISA, having a signal-to-noise ratio larger than that of astrophysical foregrounds. Our first-of-its-kind study systematically combines tests at different scales, and exploits the synergy between cosmological observations and theoretical consistency requirements.
... However, the separate universe approximation is non-perturbative, and the stochastic approach captures super-Hubble evolution beyond linear order, including non-Gaussian features. This is important for the strongest perturbations that collapse into primordial black holes (PBHs) [12,13]. Over recent years, stochastic inflation has gained popularity as the tool of choice for studying PBH statistics, see, e.g., . ...
... This excludes numerical methods that mix different time steps, such as leapfrog integration (see, e.g.,[73]).11 The generalization to a two-dimensional Markovian case where πR is independent of ϕR and the noise depends on both is simple, although such cases don't tend to crop up in the literature on stochastic inflation.12 The notation Φj in the function arguments refers to the collection of all components of the vector Φ. ...
The It\^{o} and Stratonovich approaches are two ways to integrate stochastic differential equations. Detailed knowledge of the origin of the stochastic noise is needed to determine which approach suits a particular problem. I discuss this topic pedagogically in stochastic inflation, where the noise arises from a changing comoving coarse-graining scale or, equivalently, from `zooming in' into inflating space. I introduce a zoom-in scheme where deterministic evolution alternates with instantaneous zoom-in steps. I show that this alternating zoom-in scheme is equivalent to the It\^{o} approach in the Markovian limit, while the Stratonovich approach doesn't have a similar interpretation. In the full non-Markovian setup, the difference vanishes. The framework of zoom-in schemes clarifies the relationship between computations in stochastic inflation, linear perturbation theory, and the classical formalism. It informs the numerical implementation of stochastic inflation and is a building block for a first-principles derivation of the stochastic equations.
... This is derived from the quantum mechanical interpretation of black hole horizons, in which microstates represent various quantum configurations of the horizon. Additionally, it should be noted that in his early works, S. Hawking et al. [16,17] provided particular focus to the exceptional role of PBHs in his cosmological research. ...
... Here, n 0 , p + and e − represent neutrons, protons, and electrons respectively. Through these sequential interactions, PBHs can contribute to the production of baryonic matter, aiding in the synthesis of fundamental particles necessary for nucleosynthesis and the eventual formation of atomic nuclei [16,73,83,99]. Now, we can easily determine the restriction imposed on the "productive" quantum numbers of the respective PBHs following Eq. ...
This study presents an algebraic framework to explore the fundamental relationship between gravity and quantum mechanics, with particular emphasis on the role of primordial black holes (PBHs) in cosmology. Through the concept of self-gravitating condensed light, specifically in the form of a photon Bose-Einstein condensate, this work examines the quantum attributes of PBHs and their implications for early universe dynamics, baryogenesis, and the formation of large-scale structures. The model also investigates quantized characteristics of black holes, such as mass, entropy, and temperature, suggesting that quantum processes are fundamental to black hole mechanics. By addressing issues like the cosmological constant problem and the information loss paradox, this work provides insights into Planck-scale physics and proposes that PBHs may serve as a bridge between quantum theory and general relativity. This study ultimately posits that understanding black hole physics is essential to resolving major cosmological and astrophysical paradoxes for the ultimate unification of quantum mechanics with gravity.
... However, there are a number of possibilities that do not require invoking interactions between DM and SM beyond that of gravity. A well-known example is the case of primordial black holes, produced in the early Universe [2][3][4][5][6], that are sufficiently long lived. ...
... We choose to examine the dynamics which requires ξ ≫ 1, where a more transparent treatment and clearer physical picture seem to result. 3 Let us denote the temperature at which hϕi → 0 by T Ã . ...
We examine the possibility that dark matter (DM) may be an ultralight scalar that was misaligned via nonminimal coupling to gravity, in the early Universe. For a certain regime of scalar masses, gravitational effects in neutron stars could place interesting bounds on the viable parameter space of the model, even in the absence of nongravitational interactions between DM and ordinary matter.
Published by the American Physical Society 2024
... For the heating mechanism, we investigate whether the Hawking radiation (HR) [50] emitted from early-Universe PBHs [51,52] can create the necessary conditions for the formation of large BH seeds via the direct collapse of primordial gas clouds. In this proposed mechanism, the required energy is supplied by the HR of an evaporating PBH that is still far from "exploding". ...
... PBHs are standard black holes formed in the early stages of the Universe when density fluctuations surpass a specific threshold [e.g. 51,52,58,59]. PBHs are well known as possible dark matter candidates, and most importantly ones that do not require any "new physics" to explain. The birth, lifespan, and ultimate collapse of a PBH are all based on concepts of general relativity. ...
The formation of supermassive black holes (SMBHs) in the early Universe is a subject of significant debate. In this study, we examine whether non-evaporating primordial black holes (PBHs) can offer a solution. We establish initial constraints on the range of PBH masses that correspond to Hawking radiation (HR) effective temperatures in the range needed to avoid the fragmentation of primordial gas into smaller, stellar-mass black holes. We also investigate the specific intensity of the HR from non-evaporating PBHs and compare it with the critical radiation needed for direct collapse black holes (DCBHs). We show that HR from non-evaporating PBHs cannot serve as the heating mechanism to facilitate the formation of the seeds for the SMBHs we observe in the high-redshift Universe unless, perhaps, the PBHs within the relevant mass range comprise a significant fraction of dark matter and are significantly clustered towards the center of the primordial halo.
... Primordial Black Holes (PBHs) are Black Holes (BHs) formed in the early universe, which can play a crucial role in exploring the early universe [2][3][4][5]. They are unique probes of statistical properties of the small-scale primordial inhomogeneity. ...
... Fluctuations of type I are characterized by the existence of one extremal, which corresponds to a maximum at the scale r m fulfilling the equation ζ ′ (r m ) + r m ζ ′′ (r m ) = 0 with the areal radius being a monotonic increasing function of r. Fluctuations of type II are characterized by non-monotonic behavior of the areal radius, and there are three extremal points C ′ (r) = 0 given by r m,1 , r m,2 and r m, 3 (see appendix C of [1]), two of which at r = r m1 and r m,3 correspond to two peaks 5 with the value 2/3 satisfying 1 + r m,1,3 ζ ′ (r m,1,3 ) = 0, and the rest at r = r m,2 to its minimum below 2/3 fulfilling ζ ′ (r m,2 ) + r m,2 ζ ′′ (r m,2 ) = 0. See Fig. 2 for the transition from type I to type II as increasing the amplitude. Through the transition, the first local maximum r m is split into two maxima r m,1 and r m,3 . ...
This study investigates the formation of primordial black holes (PBHs) resulting from the collapse of adiabatic fluctuations with large amplitudes and non-Gaussianity. Ref. \cite{Uehara:2024yyp} showed that fluctuations with large amplitudes lead to the formation of type B PBHs, characterized by the existence of the bifurcating trapping horizons, distinct from the more common type A PBHs without a bifurcating trapping horizon. We focus on the local type non-Gaussianity characterized by the curvature perturbation given by a function of a Gaussian random variable as with a parameter . Then we examine how the non-Gaussianity influences the dynamics and the type of PBH formed, particularly focusing on type II fluctuations, where the areal radius varies non-monotonically with the coordinate radius. Our findings indicate that, for , the threshold for distinguishing between type A and type B PBHs decreases with increasing similarly to the threshold for black hole formation. Additionally, for large positive values of , the threshold for type B PBHs approaches that for type II fluctuations. We also find that, for a sufficiently large negative value of , the threshold value is in the type II region of , i.e., there are fluctuations of type II that do not form black holes. Lastly, we calculate the PBH mass for several values of . Then we observe that the final mass monotonically increases with the initial amplitude within the parameter region of type A PBHs, which differs from previous analytical expectations.
... Even if the idea of a gravitational collapsed core was proposed in 1967 by Zeldovich and Novikov [43], they did not accurately addressed the subtleties of these "cores" in an expanding primordial background. It was Hawking and his student Carr who finally understood and analyzed, some years later, the formation of such objects [44,45] and their evaporation [46,47]. The lifetime of a PBH, t ev , is proportional to the cube of its initial mass i.e. t ev ∝ M 3 in , suggesting that a heavier (lighter) PBH will have a longer (shorter) lifetime. ...
... where γ represents the efficiency factor for collapse, and γ ∼ 0.2 (for radiation domination) [44], or γ ∼ w ...
We calculate the gravitational waves (GWs) produced by primordial black holes (PBHs) in the presence of the inflaton condensate in the early Universe. Combining the GW production from the evaporation process, the gravitational scattering of the inflaton itself, and the density fluctuations due to the inhomogeneous distribution of PBHs, we propose for the first time a complete coherent analysis of the spectrum, revealing three peaks, one for each source. Three frequency ranges ( kHz, GHz, and PHz, respectively) are expected, each giving rise to a similar GW peak amplitude . We also compare our predictions with current and future GWs detection experiments.
... The recent observations by the LIGO instrument [1][2][3], while confirming the presence of gravitational waves, have opened new questions about the origin of black holes of such masses. First studied in [4][5][6], Primordial Black Holes (PBHs) are BHs formed at very early times not as endpoint of stellar evolution, but as a consequence of different possible mechanisms. Therefore, a speculation comes to mind: has LIGO detected primordial black holes [8]? ...
It has been recently suggested that small mass black holes (BHs) may become unstable due to quantum-gravitational effects and eventually decay, producing radiation, on a timescale shorter than the Hawking evaporation time. We argue that the existence of a population of low-mass Primordial Black Holes (PBHs) acting as a fraction of the Universe dark matter component can be used to test proposed models of quantum decay of BHs via their effect on galaxy number counts. We study what constraints future galaxy clustering measurements can set on quantum-gravity parameters governing the BH lifetime and PBH abundance. In case of no detection of such effects, this would rule out either the existence of a non-negligible number of small PBHs, or the BH quantum decay scenario (or both). In case of independent observations of PBHs, the observables discussed here could be used to study the quantum effects that modify the final fate of BHs.
... The possibility that density fluctuations in the early universe collapsed into primordial black holes (PBH) has been studied for several decades [1]. Apart from their potential utility as a probe of the primordial universe, PBH are an excellent candidate for cosmological dark matter, as sufficiently large black holes are stable and dynamically cold. ...
The advent of gravitational wave astronomy has rekindled interest in primordial black holes (PBH) as a dark matter candidate. As there are many different observational probes of the PBH density across different masses, constraints on PBH models are dependent on the functional form of the PBH mass function. This complicates general statements about the mass functions allowed by current data, and, in particular, about the maximum total density of PBH. Numerical studies suggest that some forms of extended mass functions face tighter constraints than monochromatic mass functions, but they do not preclude the existence of a functional form for which constraints are relaxed. We use analytical arguments to show that the mass function which maximizes the fraction of the matter density in PBH subject to all constraints is a finite linear combination of monochromatic mass functions. We explicitly compute the maximum fraction of dark matter in PBH for different combinations of current constraints, allowing for total freedom of the mass function. Our framework elucidates the dependence of the maximum PBH density on the form of observational constraints, and we discuss the implications of current and future constraints for the viability of the PBH dark matter paradigm.
... Astrophysical black holes, whose masses typically range from few solar masses to billions of solar masses, are pretty well described by general relativity. There might exist, however, a new breed of black holes with masses below 10 12 kg, that have been produced in early Universe epochs due to the extreme matter density fluctuations [1] and/or for quantum mechanical decay of deSitter space [2][3][4]. Such black holes, one can term microscopic black holes, have sizes of elementary particles and are subject to quantum mechanical effects. ...
Recently a short scale modified black hole metric, known as holographic metric, has been proposed in order to capture the self-complete character of gravity. In this paper we show that such a metric can reproduce some geometric features expected from the quantum N-portrait beyond the semi-classical limit. We show that for a generic N this corresponds to having an effective energy momentum tensor in Einstein equations or, equivalently, non-local terms in the gravity action. We also consider the higher dimensional extension of the metric and the case of an AdS cosmological term. We provide a detailed thermodynamic analysis of both cases, with particular reference to the repercussions on the Hawking-Page phase transition.
... This may trigger an augmented enough power spectrum for wavelenghts smaller than CMB length scales. Whether this is adequate to implement a strong enough USR phase, pertinent to production of primordial black holes [26][27][28][29][30][31][32][33][34][35], and be compatible with cosmological data, will be discussed when considering particular models. ...
We consider gravitationally induced corrections to inflaton potentials driven by supersymmetry breaking in a five-dimensional supergravity, compactified on a orbifold. The supersymmetry breaking takes place on the hidden brane and is transmitted to the visible brane through finite one loop graphs giving rise to an inflaton potential which includes gravitationally induced terms. These corrections are significant for inflationary cosmology and have the potential to modify the predictions of widely studied supergravity models if the latter are embedded in this framework. To explore these effects we examine two classes of models those inspired by no-scale supergravity models and -attractors. Both models are compatible with current cosmological observations but face chalenges in reconciling enhanced values for the scalar power spectrum with cosmological data, particularly regarding the tensor to scalar ratio r. In fact results to , outside the limits put by current data.
... PBHs are formed during the early stages of the Universe, originating from the gravitational collapse of overdense regions that are excessively massive [19][20][21][22]. The excessive mass density in these regions is attributed to significant curvature perturbations (see e.g., [23][24][25][26][27][28][29][30][31]), which are more pronounced at scales much smaller than those observed in the cosmic microwave background [32]. ...
As a promising dark matter candidate, primordial black holes (PBHs) lighter than ∼ 10⁻¹⁸ M ⊙ are supposed to have evaporated by today through Hawking radiation. This scenario is challenged by the memory burden effect, which suggests that the evaporation of black holes may slow down significantly after they have emitted about half of their initial mass. We explore the astrophysical implications of the memory burden effect on the PBH abundance by today and the possibility for PBHs lighter than ∼ 10⁻¹⁸ M ⊙ to persist as dark matter. Our analysis utilizes current LIGO-Virgo-KAGRA data to constrain the primordial power spectrum and infer the PBH abundance. We find a null detection of scalar-induced gravitational waves that accompanied the formation of the PBHs. Then we find that PBHs are ruled out within the mass range ∼ [10⁻²⁴,10⁻¹⁹]M ⊙. Furthermore, we expect that next-generation gravitational wave detectors, such as the Einstein Telescope and the Cosmic Explorer, will provide even more stringent constraints. Our results indicate that future detectors can reach sensitivities that could rule out PBH as dark matter within ∼ [10⁻²⁹ M ⊙,10⁻¹⁶ M ⊙] in the null detection of scalar-induced gravitational waves.
... Given its electromagnetic inertness, efforts to reveal DM's nature focus on gravitational effects and possible nongravitational interactions with standard model particles [2], aiming to constrain its fundamental properties and role in the universe. Viable DM candidates span an extensive mass range, from ultralight scalars [3] around ∼ 10 −22 eV to primordial black holes (PBHs) up to masses 10 (3−5) M ⊙ [4,5], covering more than 80 orders of magnitude. In this study, we focus on non-annihilating, heavy DM particles [6,7] that, upon capture and accumulation within stars, may form low-mass black holes-a scenario incompatible with standard stellar evolution theory. ...
Galactic dark matter (DM) particles, having non-gravitational interactions with nucleons, can interact with stellar constituents and eventually become captured within stars. Over the lifetime of the celestial body, these non-annihilating, heavy DM particles may accumulate and eventually form a comparable stellar mass black hole (BH), referred to as a Transmuted Black Hole (TBH). We investigate how current gravitational wave (GW) experiments could detect such particle DM through the presence of low-mass TBHs, which cannot form via standard stellar evolution. Different stellar objects (compact and non-compact) provide laboratories across DM-nucleon interaction regimes, offering insight into DM's mass and its non-gravitational properties.
... The concept of Primordial Black Holes (PBHs) [1][2][3], explored for over half a century, has been revitalized after the LIGO and VIRGO collaboration's groundbreaking detection of Gravitational Waves (GWs) from black hole mergers. PBHs, spanning masses from M PBH ∼ 0.1 g to hundreds of solar masses, exhibit fascinating physical properties. ...
Blue-tilted Gravitational Waves (BGWs) have been proposed as a potential candidate for the cosmic gravitational waves detected by Pulsar Timing Arrays (PTA). In the standard cosmological framework, BGWs are constrained in their frequency range by the Big Bang Nucleosynthesis (BBN) limit on GW amplitude, which precludes their detection at interferometer scales. However, introducing a phase of early matter domination dilutes BGWs at higher frequencies, ensuring compatibility with both the BBN and LIGO constraints on stochastic GWs. This mechanism allows BGWs to align with PTA data while producing a distinct and testable GW signal across a broad frequency spectrum. Ultralight Primordial Black Holes (PBHs) could provide the required early matter-dominated phase to support this process. Interpreted through the lens of BGWs, the PTA results offer a way to constrain the parameter space of a new scenario involving modified Hawking radiation, known as the ``memory burden" effect, associated with ultralight PBHs. This interpretation can be further probed by high-frequency GW detectors. Specifically, we demonstrate that PBHs as light as can leave detectable imprints on BGWs at higher frequencies while remaining consistent with PTA observations.
... BBHs might also originate as part of a primordial BH population in the early Universe (B. J. Carr & S. W. Hawking 1974;Bird et al. 2016;Y. Ali-Haïmoud et al. 2017; Y. Wu 2020; K. K. Y. Ng et al. 2022;Z.-C. ...
Ninety gravitational-wave events have been detected by the LIGO–Virgo–KAGRA network and are released in the Gravitational-Wave Transient Catalog. Among these events, 83 cases are definitely binary black hole mergers, since the masses of all the objects involved significantly exceed the upper limit of neutron stars. The black holes in these merger events naturally form two interesting samples, a premerger sample that includes all the black holes before the mergers and a postmerger sample that consists of the black holes generated during the merging processes. The former represents black holes that once existed in the Universe, while the latter represents newly born black holes. Here we present a statistical analysis of these two samples. The nonparametric τ statistic method is adopted to correct for the observational selection effect. The Lynden-Bell C ⁻ method is further applied to derive the mass distribution and density function of black holes. It is found that the mass distribution can be expressed as a broken power-law function. More interestingly, the power-law index in the high-mass region is comparable for the two samples. The number density of black holes is found to depend on redshift as ρ ( z ) ∝ z −2.06 — z −2.12 based on the two samples. The implications of these findings on the origin of black holes are discussed.
... If the vector fields switch on only at late time, the power spectrum is enhanced on small scales, making the formations of PBHs in the radiation era is possible [51,52]. These PBHs can be candidates for dark matter [53][54][55] and supermassive black holes in our universe [56]. The enhancement of the power spectrum due to heavy fields is studied recently in multiple scalar-field models, and is used to discuss PBHs formation [57][58][59]. ...
We revisit inflation coupled with vector fields employing kinetic coupling in the comoving gauge. It is known that there is a cumulative effect IN ² on the curvature power spectrum. For a large number of e-foldings N, this contribution is so significant that it could violate observational constraints when the ratio of kinetic energy between the vector fields and the inflaton I is not extremely small. In this paper, we explore a regime where I ≫ 1. This regime has not been extensively explored due to the limitations of perturbative methods. We found that the entropy perturbation becomes heavy in this regime and the cumulative effect decays away on super-horizon scales. Consequently, the power spectrum retains its scale invariance in the decoupling limit. By straightforwardly integrating out the heavy modes near horizon-crossing, we derive a low-energy effective field theory describing a massless adiabatic perturbation with an imaginary speed of sound c s ² = -1/3. Namely, the inflation with vector fields presents a potential mechanism for generating primordial black holes.
... One significant focus in contemporary cosmology is the formation of primordial black holes (PBHs) [16][17][18], which has drawn increasing attention due to its implications for dark matter and early universe phenomena. Certain inflationary models predict amplification of small-scale curvature perturbations, potentially reaching non-linear scales. ...
\texttt{PSpectCosmo} is a high-performance \texttt{C++} program developed to investigate early-universe cosmological dynamics, with a specific emphasis on the inflationary epoch. Utilizing a Fourier-space pseudo-spectral method, \texttt{PSpectCosmo} enables the precise evolution of interacting scalar fields and gravitational waves, ensuring accurate representation of the power spectrum during inflation. This approach overcomes key limitations of finite difference methods, particularly in maintaining consistency between effective and lattice wave vectors. The code employs the adaptive step size velocity-Verlet algorithm for time integration, offering a balance of numerical stability and high precision. Additionally, \texttt{PSpectCosmo} incorporates a robust mechanism to compute convergent energy density, effectively resolving the issue of divergent energy density at the onset of inflation. These capabilities establish \texttt{PSpectCosmo} as a reliable and versatile tool for probing non-linear cosmological phenomena and inflationary dynamics with exceptional accuracy. The code is publicly available at \href{https://github.com/JieJiang-Cosmology/PSpectCosmo.git}{https://github.com/JieJiang-Cosmology/PSpectCosmo.git}.
... The stability and evolution of such macroscopic objects is similarly important. For a number of reasons which we detail here and will further elaborate upon in a forthcoming study, of particular interest is the question of whether primordial black holes [13][14][15][16][17][18][19][20][21] could result from such interacting, rich dark sectors. ...
Fermi balls are non-topological solitons that can naturally form in an early universe containing a dark sector with heavy fermions and an attractive interaction mediated by a light scalar field. We compute the Fermi ball mass and radius scaling relations when the potential of the scalar field has a non-negligible quartic coupling . The resulting Fermi balls reach `saturation' very rapidly, even when their radius is much smaller than the effective Yukawa force range. These objects can therefore grow by mergers or by accretion of ambient dark fermions, until they become so dense that they fall within their Schwarzschild radius and collapse to black holes. This setup, therefore, provides an example of a rather natural and economical dark sector scenario for the formation of primordial black holes.
... There is a tremendous amount of literature on the interesting subject of PBH formation, see, e.g., [25][26][27][28][29][30][31][32][33], and reference therein. Our goal in this section will be to outline a new mechanism for the PBH formation due to the anomalyon fluctuations. ...
We study inflation in a recently proposed gravitational effective field theory describing the trace anomaly. The theory requires an additional scalar which is massless in the early universe. This scalar -- referenced as an anomalyon -- couples to the familiar matter and radiation through the gauge field trace anomaly. We derive a class of cosmological solutions that deviate from the standard inflationary ones only slightly, in spite of the fact that the anomalyon has a sizable time dependent background. On the other hand, the scalar cosmological perturbations in this theory are different from the conventional inflationary perturbations. The inflaton and anomalyon perturbations mix, and one of the diagonal combinations gives the standard nearly scale-invariant adiabatic spectrum, while the other combination has a blue power spectrum at short distance scales. We argue that this blue spectrum can lead to the formation of primordial black holes (PBHs) at distance scales much shorter than the ones tested in CMB observations. The resulting PBHs can be heavy enough to survive to the present day universe. For natural values of the parameters involved the PBHs would constitute only a tiny fraction of the dark matter, but with fine-tunings perhaps all of dark matter could be accounted by them. We also show that the theory predicts primordial gravitational waves which are almost identical to the standard inflationary ones.
... Curvaton models can also generate a sizable amount of non-Gaussianity , which is one of the detectable signals in the observables. Eccentric objects such as primordial black holes [39][40][41][42] could also be generated in curvaton scenarios [43][44][45][46][47][48][49][50][51][52][53][54][55][56][57][58] to explain the recently observed spectrum of gravitational waves. ...
The curvaton paradigm can realise a part of or all the observed curvature perturbation. Based on the stochastic formalism of inflation and closed-form exact distributions therein, the distribution of the curvature perturbation is presented in an analytical manner by identifying a test field with a curvaton. The parameter space consisting of the decay rate and the mass of the curvaton is studied to discuss the probability that the curvaton can contribute to the curvature perturbation in a non-negligible way.
... It is of great interest to consider that the core of the GA is a primordial black hole (PBH), which is believed to be relics of the early universe inhomogeneities [17][18][19][20]. 1 Therefore, 1 Depending on their mass range, PBHs could potentially explain all or part of dark matter in the universe, as recently reviewed in [21,22]. The first detection of binary black hole mergers by LIGO/Virgo in 2016 [23] raised the possibility that the observed black holes might be PBHs [24][25][26], thus garnering increased attention for PBHs. ...
We propose a scenario of primordial gravitational atoms (PGAs), which may exist in the current and past universe due to spinning primordial black holes (PBHs) and very light bosonic fields. In a monochromatic mass scenario with a sizable dimensionless spin, which may arise in a short matter dominated (MD) era, we analyze the resulting stochastic gravitational wave background (SGWB) signal. Its spectrum is approximately characterized by a rising ∝ f ³ followed by a falling ∝ f ⁻¹ where f is the frequency. Then, we investigate the constraints and prospects of such an SGWB, and find that PGAs with a core mass M BH ∼ 𝒪(10) M ⊙ and a cloud of light scalar with mass μ ∼ 𝒪 (10⁻¹³) eV could yield constraints even stronger than those from bare PBHs. Future detectors such as LISA, Taiji and TianQin are able to explore PGAs over a narrow and elongated strap in the (μ,M BH) plane, spanning over 10 orders of magnitude for the maximum spin, 10⁻⁸ M ⊙ ≲ M BH ≲ 10⁴ M ⊙, 10⁻¹⁶ eV ≲ μ ≲ 10⁻³ eV. If the PGA is dressed with a vector cloud, the SGWB signal has a much better opportunity to be probed.
... PBHs are one of the possible alternatives to the standard cold dark matter (CDM) model (e.g., [19,20] for a recent review). PBHs are thought to have formed in the early Universe, with one of the most widely studied mechanisms being the gravitational collapse of overdense regions during the radiation-dominant era following inflation [21,22]. In this scenario, one of the interesting characteristics is that PBHs can form across a wide mass range. ...
Icarus is an individual star observed near the macro-critical curve of the MACS J1149 cluster, with the magnification factor estimated to be an order of thousands. Since microlenses near the macro-critical curve influence the number of such high-magnification events, the observed occurrence of Icarus-like events is expected to provide a useful constraint on the properties of microlenses. We first study the mass and mass fraction of microlenses consistent with the observed number of events assuming a single microlens component with a monochromatic mass function, finding that stars that contribute to the intracluster light (ICL) are consistent at the 95% confidence level. We then consider the contribution of primordial black holes (PBHs), which are one of the alternatives to the standard cold dark matter, as microlenses in addition to ICL stars. The derived parameter space indicates that a large abundance of PBHs with a mass around and a fraction of PBHs to the total dark matter of cannot explain the observed number of Icarus-like events and therefore is excluded. The methodology developed in this paper can be used to place tighter constraints on the fraction of PBHs from ongoing and future observations of ultrahigh magnification events.
... The idea of black holes originating in the early universe has been explored for more than half a century [1][2][3], with Chapline [4] being the first to propose that primordial black holes (PBHs) could account for all the dark matter in the universe. Since then, the cosmological role of PBHs has been investigated, taking into consideration the possibility they could have masses that range from M ∼ O(10 4 )M pl , with M pl being the Planck mass, up to the "incredulity limit" above M ∼ 10 10 M ⊙ , where M ⊙ is a solar mass. ...
It has been recently proposed that Hawking evaporation might slow down after a black hole has lost about half of its mass. Such an effect, called “memory burden”, is parameterized as a suppression in the mass loss rate by negative powers n of the black hole entropy and could considerably extend the lifetime of a black hole. We study the impact of memory burden on the Primordial Black Hole (PBH) reheating scenario. Modified PBH evaporation leads to a significantly longer PBH dominated stage. Requiring that PBHs evaporate prior enough to Big Bang Nucleosynthesis shrinks the allowed PBH mass range. Indeed, we find that for n > 2.5 the PBH reheating scenario is not viable. The frequency of the Gravitational Waves (GWs) induced by PBH number density fluctuations is bound to be larger than about a Hz, while the amplitude of the GW spectrum is enhanced due to the longer PBH dominated phase. Interestingly, we show that, in some models, the slope of the induced GW spectrum might be sensitive to the modifications to Hawking evaporation, proving it may be possible to test the “memory burden” effect via induced GWs. Lastly, we argue that our results could also apply to general modifications of Hawking evaporation.
... In the Carr-Hawking collapse model [78] the mass of a PBH formed during a specific epoch in the radiation dominated era, originating from the Hubble reentry of a significant fluctuation mode k P BH is related to the Hubble mass during its formation [44,79] and is expressed as follows, ...
A sharp step on a chaotic potential can enhance primordial curvature fluctuations on smaller scales to the to form primordial black holes (PBHs). The present study discusses an inflationary potential with a sharp step that results in the formation of PBHs in four distinct mass ranges. Also this inflationary model allows the separate consideration of observable parameters and r on the CMB scale from the physics at small scales, where PBHs formation occur. In this work we computed the fractional abundance of PBHs () using the GLMS approximation of peak theory and also the Press-Schechter (PS) formalism. In the two typical mass windows, and , calculated using the GLMS approximation is nearly equal to 1 and that calculated via PS is of . In the other two mass windows and , obtained using GLMS approximation is 0.01 and 0.001 respectively, while calculated via PS formalism yields and . The results obtained via GLMS approximation are found to be consistent with observational constraints. A comparative analysis of obtained using the GLMS perspective and the PS formalism is also included.
... For example, a wide variety of scenarios such as the evaporation of primordial black holes (PBHs) [6][7][8][9], the decay of moduli fields [10,11], quantum fluctuations during inflation caused by a single field or multiple fields [12][13][14][15], and the collapse of cosmic string loops or domain walls [16][17][18], could exist where energy or entropy are injected locally in the early universe, leading to fluctuations in their density. Even with relatively small injections of energy, this local increase in energy can elevate the temperature of the surrounding medium. ...
We explore the potential of gravitational waves (GWs) to probe the pre-BBN era of the early universe, focusing on the effects of energy injection. Specifically, we examine a hidden sector alongside the Standard Model that undergoes a strong first-order phase transition (FOPT), producing a GW signal. Once the phase transition has completed, energy injection initiates reheating in the hidden sector, which positions the hidden sector field so that additional phase transitions can occur. This can result in a total of three distinct phase transitions with a unique three-peak GW spectrum. Among these transitions, the first and third are of the standard type, while the intermediate second transition is inverted, moving from a broken to an unbroken phase. Using polynomial potentials as a framework, we derive analytical relations among the phase transition parameters and the resulting GW spectrum. Our results indicate that the second and third transitions generate GWs with higher amplitudes than the first, with a peak frequency ratio differing by up to an order of magnitude. This three-peak GW spectrum is detectable by upcoming facilities such as LISA, BBO, and UDECIGO. Notably, the phenomenon is robust across various potentials and model parameters, suggesting that hidden sector GWs provide a powerful tool for exploring new physics scenarios in the pre-BBN era.
... On the other hand, a nonattractor regime in the inflaton potential can be featured by introducing a flat region in the potential, leading to an Ultra-Slow roll (USR) regime, which enhances the perturbations by many orders of magnitude at the scales yet unprobed by the present measurements. An important consequence of this is that such large fluctuations could undergo gravitational collapse after re-entering the horizon post-inflation resulting in Primordial Black Holes (PBHs) [19][20][21][22][23][24][25][26][27]. Since the detection of gravitational waves from binary black hole mergers by the LIGO-VIRGO collaboration [28,29], many eyes have turned towards PBHs as potential candidates. ...
Stochastic inflation, together with the formalism, provides a powerful tool for estimating the large-scale behaviour of primordial fluctuations. We construct a numerical code to capture the non-perturbative statistics of such fluctuations and test our code to obtain the exponential non-Gaussian tail of the curvature perturbations. We provide a numerical algorithm to compute the non-perturbative curvature power spectrum and apply it to slow-roll (SR) and ultra-slow-roll (USR) single-field models of inflation. For the USR case, we successfully reproduce the peak in the power spectrum, which agrees to a certain accuracy with the perturbative power spectrum. We highlight some important differences between non-perturbative and perturbative approaches that may suggest the inconsistency of the formalism at the transition stages between attractor and non-attractor regimes.
... Primordial black holes (PBHs) are hypothetical compact objects that might have been formed in the early universe [1,2]. Although various formation scenarios have been discussed (e.g., the formation in the matter-dominated universe [3], the formation from the isocurvature perturbation [4,5], and the formation from a resonant instability of cosmological perturbation during a preheating [6,7]), the widely discussed one is the gravitational collapse of the highly dense regions in the radiation-dominated universe. ...
We investigate the formation of primordial black hole (PBH) based on numerical relativity simulations and peak theory as well as the corresponding scalar induced gravitational wave (SIGW) signals in the presence of \emph{logarithmic non-Gaussianities} which has recently been confirmed in a wide class of inflation models. Through numerical calculations, we find certain parameter spaces of the critical thresholds for the type A PBH formation and reveal a maximum critical threshold value. We also find that there is a region where no PBH is produced from type II fluctuations contrary to a previous study. We then confirm that SIGW signals originated from the logarithmic non-Gaussianity are detectable in the Laser Interferometer Space Antenna if PBHs account for whole dark matter. Finally, we discuss the SIGW interpretation of the nHz stochastic gravitational wave background reported by the recent pulsar timing array observations. We find that PBH overproduction is a serious problem for most of the parameter space, while this tension might still be alleviated in the non-perturbative regime.
... (1) arXiv:2411.07469v1 [astro-ph.CO] 12 Nov 2024 ...
Primordial black holes (PBH) can arise in a wide range of scenarios, from inflation to first-order phase transitions. Light PBHs, such as those produced during preheating or at the GUT scale, could induce an early matter-dominated phase given a moderate initial abundance. During the early matter-domination, the growth of initial PBH density perturbations can trigger collapse on horizon scales, producing much heavier PBHs. While the remaining original PBHs evaporate and reheat the Universe, these massive reformed PBHs survive for an extended period of time, producing potentially observable signatures at the present. We study this PBH reformation scenario and show that those reformed PBHs can emit significant quantities of gamma rays detectable by the next generation of experiments. The rapid reheating after matter domination generates a coincident stochastic gravitational wave background, which could be within range of the upcoming CMB-S4 experiment. The PBH reformation scenario provides an intriguing possibility of decoupling the current PBH population and the initial formation mechanism from early Universe physics, while providing opportunities for observation through multi-messenger astronomy.
... P rimordial black holes (PBHs) have been proposed as a candidate for dark matter (DM), which makes up 85% of the mass in the Universe (Carr & Hawking 1974;Meszaros 1974;Carr 1975). Observations from astrophysics and cosmology, notably gravitational microlensing of stars, supernovae and quasars, and accretion effects on the cosmic microwave background, have placed stringent constraints on the PBH DM abundance under the assumption of a monochromatic PBH mass spectrum (see e.g. ...
The origin of the binary black hole mergers observed by LIGO-Virgo-KAGRA (LVK) remains an open question. We calculate the merger rate from primordial black holes (PBHs) within the density spike around supermassive black holes (SMBHs) at the center of galaxies. We show that the merger rate within the spike is comparable to that within the wider dark matter halo. We also calculate the extreme mass ratio inspiral (EMRI) signal from PBHs hosted within the density spike spiralling into their host SMBHs due to GW emission. We predict that LISA may detect of these EMRIs with signal-to-noise ratio of 5 within a 4-year observation run, if all dark matter is made up of PBHs. Uncertainties in our rates come from the uncertain mass fraction of PBHs within the dark matter spike, relative to the host central SMBHs, which defines the parameter space LISA can constrain.
... It can make natural astrophysical mechanisms responsible for the origin of black holes with mass, exceeding few Solar masses. In the expanding homogeneous and isotropic Big Bang Universe [3,4] formation of black hole of any mass is possible, if expansion can stop within the cosmological horizon [5] and Primordial Black Hole (PBH) is formed [6][7][8][9]. Formation of PBH assumes very strong inhomogeneity of early Universe. In the framework of modern paradigm of inflationary cosmology with baryosynthesis and dark matter/energy (see References [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] for review and reference), such inhomogeneity can be predicted in cosmological scenarios based on the particular models of particle theory at specific choice of their parameters. ...
Primordial black holes (PBH), if survive to the present time, can be a fraction, or even the dominant form of dark matter of the Universe. If PBH evaporate before the present time, rare forms of dark matter like superweakly interacting or supermassive particles can be produced in the course of their evaporation. Stable remnants of PBH evaporation can also play the role of dark matter candidates. In the context of the modern standard cosmology, based on inflationary models with baryosynthesis and dark matter, which find their physical grounds beyond the Standard models of elementary particles (BSM), primordial black holes acquire the important role of sensitive probes for BSM models and their parameters. It makes PBHs a profound messenger of physics of Dark Universe.
... The detection of gravitational waves (GWs) by the LIGO, Virgo and KAGRA collaborations (LVK) [1] has increased the interest in searching for sub-solar mass compact objects, as their potential primordial origin offers insights into new physics. Primordial black holes (PBHs), hypothetical remnants of the early universe [2,3], are compelling because they are viable dark matter (DM) candidates and can shed light on the early universe condition and the formation of large-scale structures [4]. Unlike black holes formed through stellar evolution, PBHs could span a wide range of masses, from microscopic to supermassive [5][6][7][8]. ...
The search for gravitational waves generated by the inspiral phase of binaries of light compact objects holds significant promise in testing the existence of primordial black holes and/or other exotic objects. In this paper, we present a new method to detect such signals exploiting some techniques typically applied in searches for continuous quasi-monochromatic gravitational waves. We describe the signal model employed and present a new strategy to optimally construct the search grid over the parameter space investigated, significantly reducing the search computing cost. Additionally, we estimate the pipeline sensitivity corroborating the results with software injections in real data from the LIGO third observing run. The results show that the method is well suited to detect long-transient signals and standard continuous gravitational waves. According to the criteria used in the grid construction step, the method can be implemented to cover a wide parameter space with slightly reduced sensitivity and lower computational cost or to focus on a narrower parameter space with increased sensitivity at a higher computational expense. The method shows an astrophysical reach up to the Galactic Center (8kpc) for some regions of the parameter space and given search configurations.
... PBHs are expected to form in the radiation dominated era (t H ∼ 1 s, [24]) due to the gravitational collapse of overdense regions, and have been proposed as non-baryonic dark matter (DM) candidates [25]. The fraction of dark matter composed by PBHs (f PBH ) have been constrained by exploring their impact on several astrophysical phenomena (see [26]), such as gamma rays emission from evaporating PBHs [27,28], microlensing effects [29,30] and disruption of wide binaries or ultra-faint dwarfs [31,32]. ...
The presence of supermassive black holes (SMBHs, ) in the first cosmic Gyr () challenges current models of BH formation and evolution. We propose a novel mechanism for the formation of early SMBH seeds based on primordial black holes (PBHs). We assume a non-Gaussian primordial power spectrum as expected in inflationary models; these scenarios predict that PBHs are initially clustered and preferentially formed in the high- fluctuations of the large-scale density field, out of which dark matter (DM) halos are originated. Our model accounts for (i) PBH accretion and feedback, (ii) DM halo growth, and (iii) gas dynamical friction. PBHs lose angular momentum due to gas dynamical friction, sink into a dense core, where BH binaries form and undergo a runaway merger, eventually leading to the formation of a single, massive seed. This mechanism starts at in rare halos ( corresponding to fluctuations), and provides massive () seeds by . We derive a physically-motivated seeding prescription that provides the mass of the seed, , and seeded halo, as a function of redshift. This seeding mechanism requires that only a small fraction of DM is constituted by PBHs, namely . We find that quasars can be explained with seeds planted at , and growing at sub-Eddington rates, . The same scenario reproduces the BH mass of GNz11 at z=10.6, while UHZ1 (z=10.1) and GHZ9 (z=10) data favour instead slightly later (), more massive () seeds. [Abridged]
... At these small scales of the universe there may exist large peaks in the amplitude of scalar perturbations which could lead to the formation of primordial black holes (PBHs), which may explain the observations of the supermassive [1,2] and stellar-mass black hole (BH) merger events detected due to the observation of gravitational wave (GW) in LIGO-VIRGO-KAGRA [3,4]. At the same time, associated with these large peaks in the amplitude of the curvature perturbation, is the production of a stochastic gravitational wave background (SGWB) at the second-order in perturbation theory which also known as scalar-induced gravitational waves (SIGW) [5][6][7]. These large density fluctuations are quite common in inflationary scenarios, for instance, when the inflaton undergoes a period of ultra-slow-roll while tracersing a very flat region of its potential (see ref. [8] for a recent review on PBHs) but sometime may involve some higher degrees of fine-tuning see Ref. [9] for details. ...
We investigate the possibility that primordial black holes (PBHs) can be formed from large curvature perturbations generated during the waterfall phase transition in a hybrid inflation model driven by an axion-like particle (ALP) . The model predicts a spectral index and a tensor-to-scalar ratio , in agreement with Planck data and potentially testable by next generation cosmic microwave background (CMB) experiments such as CMB-S4 and LiteBIRD. We find that the PBH mass and the peak of the associated scalar-induced gravitational wave (SIGW) spectrum are correlated with the ALP mass. In particular, PBHs in the mass range can constitute either the entire dark matter (DM) content of the universe or a significant fraction of it. The predicted second-order GWs from this mechanism are within the sensitivity reach of future observatories like LISA and ET. The typical reheating temperature in the model is around GeV is consistent with Big Bang Nucleosynthesis (BBN) constraints.
... However, in certain models, the inflaton potential features a flat region or shallow minimum where the deceleration becomes dominant, and the field's velocity can decrease exponentially, in what is called an "ultra-slowroll" (USR) phase [6][7][8][9][10][11]. Perturbations generated during USR are far from scale-invariant, displaying a large amplification. These perturbations may lead to interesting phenomenological consequences, such as the emission of scalar-induced gravitational waves (SIGW) [12][13][14][15][16][17][18], and/or seed primordial black hole (PBH) formation [19][20][21][22][23]. PBHs are a longstanding candidate for dark matter, potentially accounting for all dark matter or acting as seeds for supermassive black holes, see Refs. ...
Violating the slow-roll regime during the final stages of inflation can significantly enhance curvature perturbations, a scenario often invoked in models producing primordial black holes and small-scale scalar induced gravitational waves. When perturbations are enhanced, one approaches the regime in which tree-level computations are insufficient, and nonlinear corrections may become relevant. In this work, we conduct lattice simulations of ultra-slow-roll (USR) dynamics to investigate the significance of nonlinear effects, both in terms of backreaction on the background and in the evolution of perturbations. Our systematic study of various USR potentials reveals that nonlinear corrections are significant when the tree-level curvature power spectrum peaks at , with 5%10% corrections. Larger enhancements yield even greater differences. We establish a universal relation between simulation and tree-level quantities at the end of the USR phase, which is valid in all cases we consider. Additionally, we explore how nonlinear interactions during the USR phase affect the clustering and non-Gaussianity of scalar fluctuations, crucial for understanding the phenomenological consequences of USR, such as scalar-induced gravitational waves and primordial black holes. Our findings demonstrate the necessity of going beyond leading order perturbation theory results, through higher-order or non-perturbative computations, to make robust predictions for inflation models exhibiting a USR phase.
... However, we propose that these SMBHs could have come into being in the very early universe as supermassive primordial black holes (SMPBHs). Recently, the cosmological implications of PBHs (Carr & Hawking 1974;Zel'dovich & Novikov 1967;Hawking 1971) have been intensively studied, see reviews by e.g. Carr et al. (2016) Domènech & Sasaki (2024). ...
The James Webb Space Telescope (JWST) has uncovered an abundant population of compact, extremely red, and X-ray weak objects at , knows as ``Little Red Dots" (LRDs). These objects exhibit spectral energy distributions that resemble both active galactic nuclei (AGN) and stellar population templates. However, whether dominated by AGN activity or compact star formation, the high redshifts and masses/luminosities of LRDs, coupled with their significant abundance, present potential challenges to the standard CDM model. In this work, we proposes a novel cosmic interpretation of this anomaly, suggesting that these LRDs are likely massive galaxies seeded by supermassive primordial black holes (SMPBHs) came into being in the very early universe. We analyze 434 known LRDs from the 0.54 COSMOS-Web survey and test the hypothesis that they originated from SMPBHs assuming sub-Eddington accretion. According to our result, SMPBHs actually could lead to the existence of more LRDs, even at higher redshifts ().
We estimate the probability distribution for the spins of the primordial black holes (PBHs) that formed during an early matter-dominated era in the Universe. We employ the Zel'dovich approximation and focus on the linear-order effect of cosmological perturbations which causes the tidal torque. Assuming that the fluctuations obey Gaussian statistics, we apply the peak theory of random Gaussian variables to compute the root mean square (RMS) and the probability distribution of the non-dimensional Kerr parameter a * at their formation. The value of a * is evaluated through the angular momentum at the turn-around time. We find that the RMS a̅ * with a given amplitude of the fluctuation δ pk decreases as the amplitude increases. This behavior allows us to set the threshold value of the amplitude of the fluctuation through the under-extremal condition a̅ * < 1. Then we discuss the impact of spin and anisotropic collapse on the production rate of PBHs. We find that, for σ H ≤ 10⁻³ with σ H being the square root of the variance of the fluctuation at the horizon reentry, the suppression from the spin effect is dominant, while the effect of anisotropy becomes more important for σ H > 10⁻³. Since a̅ * can be written as a function of ν := δ pk/σ H, we can obtain the probability distribution of a̅ *, P(a̅ *), through the probability distribution of ν characterized by a given power spectrum of the fluctuation. P(a̅ *) depends on σ H and the parameter γ that characterizes the width of the power spectrum. It is shown that, in the parameter regions of our interests, substantial values of PBH spins are expected in contrast to the PBH formation in a radiation-dominated universe. For instance, with γ = 0.6 and σ H = 0.1, P(a̅ *) takes a maximum at aa̅ * ≃ 0.25.
We present a complete and consistent exposition of the regularization, renormalization, and resummation procedures in the setup of having a contraction and then non-singular bounce followed by inflation with a sharp transition from slow-roll (SR) to ultra-slow roll (USR) phase for generating primordial black holes (PBHs). We consider following an effective field theory (EFT) approach and study the quantum loop corrections to the power spectrum from each phase. We demonstrate the complete removal of quadratic UV divergences after renormalization and softened logarithmic IR divergences after resummation and illustrate the scheme-independent nature of our renormalization approach. We further show that the addition of a contracting and bouncing phase allows us to successfully generate PBHs of solar-mass order, , by achieving the minimum e-folds during inflation to be and in this process successfully evading the strict no-go theorem. We notice that varying the effective sound speed between , allows the peak spectrum amplitude to lie within , indicating that causality and unitarity remain protected in the theory. We analyse PBHs in the extremely small, , and the large, , mass limits and confront the PBH abundance results with the latest microlensing constraints. We also study the cosmological beta functions across all phases and find their interpretation consistent in the context of bouncing and inflationary scenarios while satisfying the pivot scale normalization requirement. Further, we estimate the spectral distortion effects and shed light on controlling PBH overproduction.
We discuss a generalization of constant-roll inflation models by using -function formalism for inflation in such a way that the exact constant-roll condition is asymptotically satisfied near the fixed points of the -functions, in other words, in deep inflationary phase. Several types of the -functions and the corresponding inflaton potentials which satisfy the generalized constant-roll condition are analytically found.
A bstract
In our quest to understand the generation of cosmological perturbations, we face two serious obstacles: we do not have direct information about the environment experienced by primordial perturbations during inflation, and our observables are practically limited to correlators of massless fields, heavier fields and derivatives decaying exponentially in the number of e-foldings. The flexible and general framework of open systems has been developed precisely to face similar challenges. Building on previous work, we develop a Schwinger-Keldysh path integral description for an open effective field theory of inflation, describing the possibly dissipative and non-unitary evolution of the Goldstone boson of time translations interacting with an unspecified environment, under the key assumption of locality in space and time. Working in the decoupling limit, we study the linear and interacting theory in de Sitter and derive predictions for the power spectrum and bispectrum that depend on a finite number of effective couplings organised in a derivative expansion. The smoking gun of interactions with the environment is an enhanced but finite bispectrum close to the folded kinematical limit. We demonstrate the generality of our approach by matching our open effective theory to an explicit model. Our construction provides a standard model to simultaneously study phenomenological predictions as well as quantum information aspects of the inflationary dynamics.
The Schwarzschild radii of primordial black holes (PBHs) in the mass range of 6 × 10 ¹⁴ –4 × 10 ¹⁹ g match the sizes of nuclei to atoms. I discuss the resulting quantum-mechanical suppression in the accretion of matter by PBHs in dense astrophysical environments, such as planets or stars.
Using the 36-foot NRAO telescope at lambda = 3.5 mm, an upper limit of ; 0.0043 deg K was set, with 90 percent confidence, on the fluctuations in thc ; cosmic microwave background. The angular scale of the measurement was ~80 deg . ; If discrete sources produce all of the microwave background, their number must ; exceed~0.35 Mpcâ»Â³. (auth);
It is suggested that there may be a large number of gravitationally collapsed objects of mass 10–5 g upwards which were formed as a result of fluctuations in the early Universe. They could carry an electric charge of up to ± 30 electron units. Such objects would produce distinctive tracks in bubble chambers and could form atoms with orbiting electrons or protons. A mass of 10¹⁷ g of such objects could have accumulated at the centre of a star like the Sun. If such a star later became a neutron star there would be a steady accretion of matter by a central collapsed object which could eventually swallow up the whole star in about ten million years.
A prescription is given for attaching to a space-time M, subject only to a causality condition, a collection of additional 'ideal points'. Some of these represent 'points at infinity', others 'singular points'. In particular, for asymptotically simple space-times, the ideal points can be interpreted as the boundary at conformal infinity. The construction is based entirely on the causal structure of M, and so leads to the introduction of ideal points also in a broad class of causal spaces. It is shown that domains of dependence can be characterized in terms of ideal points, and this makes possible an extension of the domain-of-dependence concept to causal spaces. A suggestion is made for assigning a topology to M together with its ideal points. This specifies some singular-point structure for a wide range of possible space-times.