Black Hole Production Research Articles

Enhancing gravitational wave anisotropies with peaked scalar sources

Gravitational wave (GW) backgrounds of cosmological origin are expected to be nearly isotropic, with small anisotropies resembling those of the cosmic microwave background. We analyse the case of a scalar-induced GW background and clarify in the process the relation between two different approaches to calculating GW anisotropies. We focus on GW scenarios sourced by a significantly peaked scalar spectrum, which are frequently considered in the context of primordial black holes production. We show that the resulting GW anisotropies are characterised by a distinct frequency dependence. We explore the observational consequences concentrating on a GW background enhanced in the frequency band of space-based GW detectors. We study the detectability of the signal through both cross-correlations among different space-based GW detectors, and among GW and CMB experiments.

Black hole production, eternal inflation, and information in quasi-de Sitter space

When the slow-roll parameter ϵ H is smaller than H 2/M Pl 2, the quantum fluctuations of the inflaton after the horizon crossing are large enough to realize eternal inflation. Whereas they do not generate a sufficient amount of density fluctuation of the inflaton to produce the black hole in quasi-de Sitter space, they can also generate the sizeable density fluctuation of the radiation when the number of degrees of freedom increases rapidly in time, as predicted by the distance conjecture. We argue that the condition that the density fluctuation of the radiation is not large enough to produce the black hole until the end of inflation is equivalent to the no eternal inflation condition. When the radiation emitted by the horizon does not produce the black hole, even if the number of degrees of freedom increases in time, the information paradox does not arise for ϵ H larger than 10-7 (H 2/M Pl 2) and time scale shorter than 104 (M Pl/H 2). Regardless of the presence of the information paradox, a static observer cannot retrieve a sufficient amount of information, which is consistent with the complementarity.

Primordial black-hole dark matter via warm natural inflation

We report on a study of the natural warm inflationary paradigm (WNI). We show two important new results arise in this model. One is that the observational constraints on the primordial power spectrum from the cosmic microwave background (CMB) can be satisfied without going beyond the Planck scale of the effective field theory. The second is that WNI can inevitably provide perfect conditions for the production of primordial black holes (PBHs) in the golden window of black-hole mass range (10−16−10−11M⊙) where it can account for all of the dark matter content of the universe while satisfying observational constraints.

Production of primordial black holes via single field inflation and observational constraints

In a class of single field models of inflation, the idea of primordial black holes (PBHs) production is studied. In this case, the dynamics on small cosmological scales differs significantly from that of the large scales probed by the observations of cosmic microwave background (CMB). This difference becomes a virtue in producing correct physical ambiance for the seeds required to produce PBHs. Thus, once the perturbed scales re-enter the horizon of our Universe during the later epochs of radiation domination and subsequent matter domination, these seeds collapses to produce PBHs. We have shown, in this class of model, depending on the model parameters and the class defining set parameters, one can have PBHs formed for a vast mass ranges from 10^{-18} to 10^{-6} solar mass (M _odot ). We have also shown, for a particular class of model, the total dark matter density today can be attributed to the PBHs density. The vast range of the mass depending on the class parameter, gives ample opportunity to study enriched phenomenological implications associated with this model to probe the nascent Universe dynamics.

Primordial black holes and gravitational waves in multiaxion-Chern-Simons inflation

We study aspects of inflation and the possibility of enhanced production of primordial black holes (PBHs) and gravitational waves (GWs) in a string-inspired model of two axion fields coupled to Chern-Simons gravity, which results in a running-vacuum-model inflation. Fluctuations of the scale invariant spectrum, consistent with the cosmological data, are provided in this model by world-sheet (non-perturbative) instanton terms of the axion field arising from string compactification. As a result of such modulations, there is an enhanced production of PBHs and GWs in such cosmologies, which may lead to observable in principle patterns in the profile of GWs during the radiation era. Moreover, we demonstrate that the PBHs may provide a significant amount of Dark Matter in this Universe. For comparison, we also discuss a two-stage inflation cosmological model of conventional string-inspired axion monodromy, involving again two axion fields. The resulting modifications imprinted on the GWs spectra between these two classes of models are distinct, and can, in principle, be distinguished by future interferometers. We consider models with more or less instantaneous reheating. We also make some remarks on the effects of a prolonged reheating period in leading to further enhancement of the power spectrum and thus fractions of PBHs that play the role of Dark matter.

Planckian discreteness as seeds for cosmic structure

We propose a model of inflation driven by the relaxation of an initially Planckian cosmological constant due to diffusion. The model can generate a (approximately) scale invariant spectrum of (adiabatic) primordial perturbations with the correct amplitudes and red tilt without an inflaton. The inhomogeneities observable in the CMB arise from those associated to the fundamental Planckian granularity that are imprinted into the standard model Higgs scalar fluctuations during the inflationary phase. The process admits a semiclassical interpretation and avoids the trans-Planckian problem of standard inflationary scenarios based on the role of vacuum fluctuations. The deviations from scale invariance observed in the CMB are controlled by the self coupling constant of the Higgs scalar of the standard model of particle physics. The thermal production of primordial black holes can produce the amount of cold dark matter required by observations. For natural initial conditions set at the Planck scale the amplitude and tilt of the power spectrum of perturbations observed at the CMB depend only on known parameters of the standard model such as the self coupling of the Higgs scalar and its mass.

Primordial black holes and gravitational waves in teleparallel Gravity

In this paper, we consider the possible effect of the teleparallel gravity on the production of the primordial black holes (PBH) and on the gravitational waves (GWs). We investigate the relationship between the slow roll, the e-folds number and the teleparallel parameters. We show that in the case of the teleparallel parameter delta =3, the e-folds number reaches the values 50 and 60 in consistency with the contour plot of the (r,n_{s}) plane obtained by Planck data at 1sigma and 2sigma C.L. Furthermore, we use the fraction of the energy density and the variance of the density perturbations approach to study the abundance of the production PBH. We find that the PBH overproduction can be satisfied for specific values of parameters of the non-adiabatic curvature power spectrum at some narrow parametric resonance. Moreover, to explain the GWs expected by observations, the duration of preheating should be bounded by values less or equal to 2. This bound is in agreement with values of the tensor-to-scalar ratio and the spectral index constrained by Planck data.

Inflation with two-form field: the production of primordial black holes and gravitational waves

Antisymmetric tensor field (two-form field) is a ubiquitous component in string theory and generally couples to the scalar sector through its kinetic term.In this paper, we propose a cosmological scenario that the particle production of two-form field, which is triggered by the background motion of the coupled inflaton field, occurs at the intermediate stage of inflation and generates the sizable amount of primordial black holes as dark matter after inflation. We also compute the secondary gravitational waves sourced by the curvature perturbation and show that the resultant power spectra are testable with the future space-based laser interferometers.

Non-Gaussianity and secondary gravitational waves from primordial black holes production in alpha -attractor inflation

We study the non-Gaussianity and secondary Gravitational Waves (GWs) in the process of the Primordial Black Holes (PBHs) production from inflation. In our work, we focus on the alpha -attractor inflation model in which a tiny bump in the inflaton potential enhances the amplitude of the curvature perturbations at some scales and consequently leads to the PBHs production with different mass scales. We implement the computational code BINGO which calculates the non-Gaussianity parameter in different triangle configurations. Our examination implies that in this setup, the non-Gaussianity gets amplified significantly in the equilateral shape around the scales in which the power spectrum of the scalar perturbations undergoes a sharp declination. The imprints of these non-Gaussianities can be probed in the scales corresponding to the BBN and mu -distortion events, or in smaller scales, and detection of such signatures in the future observations may confirm the idea of our model for the generation of PBHs or rule it out. Moreover, we investigate the secondary GWs in this framework and show that in our model, the peak of the present fractional energy density is obtained as Omega _{mathrm{GW0}} sim 10^{-8} at different frequencies which depends on the model parameters. These results lie well within the sensitivity region of some GWs detectors at some frequencies, and therefore the observational compatibility of our model can be evaluated by the forthcoming data from these detectors. We further provide some estimations for the tilts of the induced GWs spectrum in the different intervals of frequency, and demonstrate that the spectrum obeys the power-law relation Omega _{mathrm{GW0}}sim f^{n} in those frequency bands.

Effects of non-standard interaction on microscopic black holes from ultra-high energy neutrinos

If the universe has more than 4-dimensions, the TeV scale gravity theories predict formation of microscopic black holes due to interaction of ultra high energy neutrinos coming from some extragalactic origin with the nucleons present in the Earth’s atmosphere. The decay of these black holes can generate high multiplicity events which can be detected through neutrino telescopes. Ultra high energy neutrinos can also produce events without the formation of black holes which can be distinguished from the black hole events depending on their topological structure. In this work we study the effects of non-standard interaction on the production of these shower events. We find that new physics has inconsequential impact on the number of events produced through the generation of black holes. For events produced without the formation of black holes, new physics can only provide a marginal deviation. Therefore a large enhancement in the number of shower events over the standard model prediction can provide unambiguous signatures of TeV scale gravity in the form of microscopic black hole production.

The effect of multiple features on the power spectrum in two-field inflation

We extend our previous workon the enhancement of the curvature spectrum during inflation to the two-field case.We identify the slow-roll parameter η as the quantitythat can trigger the rapid growth of perturbations.Its two components, η ∥ along the background trajectoryand η ⊥ perpendicular to it, remain small during most of the evolution,apart from short intervals during which they take large, positive or negative, values.The typical reason for the appearance of strong features in η ∥ issharp steps or inflection points in the inflaton potential,while η ⊥ grows large during sharp turns infield space. We focus on the additive effect of several featuresleading to the resonant growth of the curvature spectrum.Three or four features in the evolution of η are sufficient in order to induce an enhancement of the power spectrum by six or seven orders of magnitude, which canlead to the significant production of primordial black holes and stochasticgravitational waves.A big part of our study focuses on understanding the evolutionof the perturbations and the resulting spectra through analytic means.The presence of multiple features inthe background evolution points to a more complex inflationary paradigm,which is also more natural in the multi-field case.The critical examination of this possibility is withinthe reach of experiment.

Enhanced power on small scales and evolution of quantum state of perturbations in single and two field inflationary models

With the detection of gravitational waves from merging binary black holes, over the last few years, there has been a considerable interest in the literature to understand if these black holes could have originated in the early universe. If the primordial scalar power over small scales is boosted considerably when compared to the COBE normalized amplitude over large scales, then, such an increased power can lead to a copious production of primordial black holes that can constitute a significant fraction of the cold dark matter density today. Recently, many models of inflation involving single or two scalar fields have been constructed which lead to enhanced power on small scales. In this work, we examine the evolution of the quantum state of the curvature perturbations in such single and two field models of inflation using measures of squeezing, entanglement entropy or quantum discord. We find that, in the single as well as the two field models, the extent of squeezing of the modes is enhanced to a certain extent (when compared to the scenarios involving only slow roll) over modes which exhibit increased scalar power. Moreover, we show that, in the two field models, the entanglement entropy associated with the curvature perturbation, arrived at when the isocurvature perturbation has been traced out, is also enhanced over the small scales. We also take the opportunity to discuss the relation between entanglement entropy and quantum discord in the case of the two field model. We conclude with a brief discussion on the wider implications of the results.

Secondary GWs and PBHs in string inflation: formation and detectability

We derive the spectrum and analyse the detectability prospects of secondary gravity waves (GWs) associated to primordial black hole (PBH) production in a class of string inflationary models called Fibre Inflation. The inflationary potential features a near inflection point that induces a period of ultra slow-roll responsible for an enhancement of the scalar perturbations which can lead to PBHs with different masses and contributions to dark matter (DM) in agreement with current observational bounds, including CMB constraints on the scalar spectral index and the tensor-to-scalar ratio. This enhancement of the curvature perturbations sources secondary GWs which can be detected by either LISA, ET or BBO, depending on the GW frequency but regardless of the amount of PBH DM since secondary GWs remain detectable even if the PBH contribution to DM is exponentially suppressed. The possibility to see a secondary GW signal is instead due to the presence of an ultra slow-roll epoch between CMB horizon exit and the end of inflation.

Dilaton-axion inflation with PBHs and GWs

We discuss two-stage dilaton-axion inflation models [1] and describe α-attractor models with either exponential or polynomial approach to the plateau.We implement one of the models of primordial black hole production proposed in [2] in the α-attractor context, and develop its supergravity version. The predictions of this model following from its polynomial attractor properties are: ns and r are α-independent, r depends on the mass parameter μ defining the approach to the plateau. The tachyonic instability at the transition point between the two stages of inflation is proportional to the negative curvature of the hyperbolic space ℛK = -2/3α. Thereforethe masses of primordial black holes (PBHs) and the frequencies of small-scale gravitational waves (GWs) in this model show significant dependence on α.

Non-Gaussianity in inflationary scenarios for primordial black holes

Working in an idealised framework in which a series of phases of evolution defined by the second slow-roll parameter η are matched together, we calculate the reduced bispectrum, f NL, for models of inflation with a large peak in their primordial power spectra. We find f NL is typically approximately constant over scales at which the peak is located, and provide an analytic approximation for this value. This allows us to identify the conditions under which f NL is large enough to have a significant impact on the resulting production of primordial black holes (PBHs) and scalar induced gravitational waves (SIGWs). Together with analytic formulae for the gradient of the rise and fall in the power spectrum, this provides a toolkit for designing or quickly analysing inflationary models that produce PBHs and SIGWs.

Revisiting small-scale fluctuations in α-attractor models of inflation

Cosmological α-attractors stand out as particularly compelling models to describe inflation in the very early universe, naturally meeting tight observational bounds from cosmic microwave background (CMB) experiments. We investigate α-attractor potentials in the presence of an inflection point, leading to enhanced curvature perturbations on small scales. We study both single- and multi-field models, driven by scalar fields living on a hyperbolic field space.In the single-field case, ultra-slow-roll dynamics at the inflection point is responsible for the growth of the power spectrum, while in the multi-field set-up we study the effect of geometrical destabilisation and non-geodesic motion in field space. The two mechanisms can in principle be distinguished through the spectral shape of the resulting scalar power spectrum on small scales. These enhanced scalar perturbations can lead to primordial black hole (PBH) production and second-order gravitational wave (GW) generation.Due to the existence of universal predictions in α-attractors, consistency with current CMB constraints on the large-scale spectral tilt implies that PBHs can only be produced with masses smaller than 108 g and are accompanied by ultra-high frequency GWs, with a peak expected to be at frequencies of order 10 kHz or above.

Stochastic effects in axion inflation and primordial black hole formation

We revisit the model of axion inflation in the context of stochastic inflation and investigate the effects of the stochastic noises associated to the electromagnetic fields. Because of the parity violating interaction, one polarization of the gauge field is amplified inducing large curvature perturbation power spectrum. Taking into account the stochastic kicks arising from the short modes at the time of horizon crossing we obtain the corresponding Langevin equations for the long modes of the electromagnetic and axion fields. It is shown that a mean-reverting process governs the dynamics of the electromagnetic fields such that the tachyonic growth of the gauge fields is balanced by the diffusion forces. As the instability parameter grows towards the end of inflation, the large curvature perturbations induced from gauge field perturbations lead to copious production of small mass primordial black holes (PBHs). It is shown that the produced PBHs follow a Gaussian statistics. Imposing the observational constraints on PBHs formation relaxes the previous bounds on the instability parameter by about fifty percents.

Implications of stochastic effects for primordial black hole production in ultra-slow-roll inflation

We study the impact of stochastic noise on the generation of primordial black hole (PBH) seeds in ultra-slow-roll (USR) inflation with numerical simulations. We consider the non-linearity of the system by consistently taking into account the noise dependence on the inflaton perturbations, while evolving the perturbations on the coarse-grained background affected by the noise. We capture in this way the non-Markovian nature of the dynamics, and demonstrate that non-Markovian effects are subleading. Using the ΔN formalism, we find the probability distribution P(ℛ) of the comoving curvature perturbation ℛ. We consider inflationary potentials that fit the CMB and lead to PBH dark matter with i) asteroid, ii) solar, or iii) Planck mass, as well as iv) PBHs that form the seeds of supermassive black holes. We find that stochastic effects enhance the PBH abundance by a factor of \U0001d4aa(10)–\U0001d4aa(108), depending on the PBH mass. We also show that the usual approximation, where stochastic kicks depend only on the Hubble rate, either underestimates or overestimates the abundance by orders of magnitude, depending on the potential. We evaluate the gauge dependence of the results, discuss the quantum-to-classical transition, and highlight open issues of the application of the stochastic formalism to USR inflation.

Evolution of the Periodic Table as We Know it?

The inversion of the Periodic Table to accommodate spatial variation of atomic energy levels relative to the nucleus has subsequently been underwritten by Quantum Field Theory’s U(1) x SU(2) x SU(3) group symmetry and Clifford Algebra resulting in a one-to-one mapping between the Roberts-Janet Nuclear Periodic Table and the Quantum Mechanical Table. A coherent sketch of scientific commentary is attempted in the form of two cycles within the Roberts-Janet Table. Mechanisms of superposition, entanglement, tunnelling and decoherence abound but the pathways of causality remain elusive; whether testable as telescopes and artificial intelligence evolve. Mass number is no longer a fundamental property. It appears unique to each supernova explosion as the ratio of isotopes varies in the nth decimal place as radioactivity proceeds. Goodbye a unique Periodic Table. Hello a large number of Periodic Tables underwritten by the Roberts-Janet mechanism where mass number is merely a by-product. The first cycle reignites radioactivity by mergers between neutron stars and black holes - radioactivity having been extinguished temporarily in the ebb and flow of production of white dwarfs, neutron stars and black holes. Nuclei with large mass numbers and low atomic numbers result; rapidly decaying to nuclei with large atomic numbers. By further decay elements familiar to the Periodic Table appear from higher atomic numbers. Various sizes of black hole production suggest a hierarchy of outcomes which not only produce a reignition of radioactivity but potential creations of other universes from explosions of larger and supermassive black holes as the Planck length is approached and energies increase to a scale giving rise to periods of inflation and condensation that predate the production of quarks. This implies universes can be superimposed on previous universes explaining why some supermassive black holes appear in subsequent universes nearer than current theoretical models. The second cycle indicates a path through abiogenesis, water and trace elements to form life ultimately to be extinguished by the Sun’s expansion thus merging with the first cycle’s production of stars.

Letter To Feynman, Einstein, Wallace, Darwin, Maxwell and Mendeleev

The Roberts-Janet Nuclear Periodic Table has emerged recently. The inversion of the Periodic Table to accommodate spatial variation of atomic energy levels relative to the nucleus has subsequently been underwritten by Quantum Field Theory’s U (1) X SU (2) x SU (3) group symmetry and Clifford Algebra resulting in a one-toone mapping between the Roberts-Janet Table and The Quantum Mechanical Table. This manuscript attempts to show the over-arching nature of the Roberts-Janet Table epitomised by two cycles. The first of these is the role of causality within the lower half of the table in nucleosynthesis and cosmology whilst the second attempts to outline causality’s path in the upper half of the table in biochemical settings. The link between the cycles is the set of elements themselves; within theoretically an infinite group of elements as radioactivity is reignited having been extinguished temporarily in the ebb and flow of production and annihilation of white dwarfs, neutron stars and black holes. The current scientific landscape is outlined to create a platform from which to proceed. Various sizes of black hole production suggest a hierarchy of outcomes which produces a reignition of radioactivity and potentially a creation of other universes from the explosions of larger supermassive black holes as energies increase to the Planck scale resulting in periods of inflation and condensation that predate quark production. Universes could be superimposed on previous universes explaining why some supermassive black holes appear nearer than current theoretical models.