arXiv subjects

Albert Escrivà

Publications and source records attributed to Albert Escrivà.

At least 19 recordsLinked to original sources

arXiv2026

Simulation of PBH formation in a matter-dominated universe

We investigate primordial black hole (PBH) formation during an early matter-dominated era using fully nonlinear numerical relativity. The initial condition is set by a functional form of the curvature perturbation including ellipticity, which makes the configuration triaxial. Two kinds of matter descriptions are considered: dust fluid and collisionless particles. In the dust fluid description, numerical computation crashes associated with the appearance of a singularity at which the fluid density diverges, unless the singularity is hidden well inside the apparent horizon. We found that, for the dust fluid description, to observe the horizon formation before calculations crash, the initial amplitude must be larger than the previous analytic estimation by a factor of 2. On the other hand, with the particle system description, calculations do not crash, and we may observe black hole formation after subsequent evolution of the system. Then the threshold of black hole formation is significantly smaller than the previous analytic estimation by an order of magnitude.

gr-qc↗

arXiv2026

Primordial Asymmetries, Primordial Equation of State & Primordial Black Holes

We study the thermal history of the primordial Universe in the presence of non-zero lepton and baryon asymmetries. Considering different scenarios, we determine the equation of state (EoS) of the Universe from T = 10 GeV down to T = 1 keV, spanning the QCD transition, hadron gas phase and neutrino decoupling epochs. Using a combination of numerical codes, we track the cosmic trajectories of chemical potentials associated with the baryonic, leptonic and electric charges, and follow the evolution of lepton asymmetries including through the era where neutrino oscillations take place. Combining peak theory with numerical-relativity simulations of the collapse threshold, we show the EoS-induced modifications to the primordial black hole (PBH) mass spectrum. We determine the associated Gravitational Wave (GW) signal, showing how lepton asymmetries and a particular spectral index of curvature perturbations can be hinted at by current ground interferometer-based GW observations. Finally, we discuss constraints and positive evidence for PBHs.

astro-ph.CO↗

arXiv2026

Beyond isolated curvature peaks: collective collapse and multiple Primordial Black Hole formation

Primordial black hole (PBH) calculations usually treat rare curvature peaks as isolated collapsing regions. Using fully nonlinear $3+1$ numerical-relativity simulations in a radiation-dominated Universe, we demonstrate that neighbouring primordial curvature perturbations need not map one-to-one onto PBHs: they may ultimately disperse, collapse collectively into a single PBH, or undergo distinct local collapses and form more than one PBH. In the family of two-component profiles studied here, the latter outcome is a pair of PBHs, identified by the coexistence of two disconnected apparent horizons on at least one time slice. We introduce a nonspherical quasi-local compaction diagnostic based on the Hawking mass and referenced to a round flat-FLRW sphere of equal area. It retains the angular structure of the curvature field and reduces to the standard Misner-Sharp compaction function in spherical symmetry. The global maximum of this diagnostic, $\mathcal K_{\rm form}$, provides an empirical indicator of whether at least one PBH forms, with a transition near $\mathcal K_{\rm form,c}\approx0.56$ and modest profile-dependent scatter. For forming bimodal profiles, we supplement the nonlinear compactness with a signed linear surface strength evaluated on the same probing spheres. The viability of the weaker local branch and the competition between the local and common-enclosing branches improve the empirical discrimination between single- and double-PBH outcomes. Our results therefore show that the maximum curvature amplitude alone does not determine the collapse outcome, which also depends on the spatial extent, characteristic scales, and geometry of the surrounding curvature environment.

astro-ph.CO↗

arXiv2026

The statistics of curvature-profile dispersion in primordial black hole formation

In the standard curvature-perturbation scenario, PBHs form from the collapse of superhorizon curvature fluctuations after horizon re-entry. The predicted abundance is exponentially sensitive to the collapse threshold and hence to the shape of the primordial curvature profile. In this work we develop a finite-action framework to describe curvature-profile dispersion around representative peak profiles. Using a multipolar Fourier-Bessel decomposition, we separate the local peak variables of the Gaussian field from residual radial and angular deformations, normalized by their Gaussian action. We apply the formalism to spherical numerical-collapse examples in order to isolate the effect of radial shape dispersion. For finite-width spectra, and in the presence of logarithmic local non-Gaussianity, we compute the collapse threshold as a function of a coherent shape variable and combine the result with peak statistics. We find that the dominant contribution to the PBH abundance is not necessarily the conditional-mean reference profile, nor simply the profile with the lowest threshold. Instead, it is selected by a competition between the Gaussian cost of realizing a coherent deformation and the exponential gain associated with lowering the collapse threshold. Broad spectra and negative non-Gaussianity can make rare shape deformations dominate the abundance. In the examples studied here, the dominant branches can correspond to several-sigma coherent shape fluctuations while enhancing the integrated abundance by orders of magnitude. Equivalently, including shape dispersion can reduce the power-spectrum amplitude required to obtain a fixed PBH abundance. Our results show that residual profile dispersion is a genuine statistical ingredient in PBH formation and can be quantitatively important for accurate abundance estimates.

astro-ph.CO↗

arXiv2026

COSMOS: A numerical relativity code specialized for PBH formation

Primordial black holes (PBHs) are black holes generated in the early universe without having gone through stellar evolution. In the standard formation process, PBHs are formed from super-horizon primordial fluctuations with non-linearly large initial amplitude. In order to simulate the non-linear gravitational dynamics of PBH formation, one has to rely on numerical relativity solvers to approximate the solution of the Einstein equations. COSMOS is a C++ package for solving the Einstein equations in 3+1 dimensions, providing simple tools for the simulation of PBH formation. In order to resolve the collapsing region, non-Cartesian scale-up coordinates and a fixed mesh-refinement procedure are implemented. In COSMOS, a massless scalar field and a perfect fluid with a linear equation of state are implemented as matter fields. To achieve a practically acceptable computational speed, OpenMP is used for the parallelization. COSMOS has no other dependencies, which makes for an easier installation.

gr-qc↗

arXiv2026

Gravitational wave emission from nonspherical collapse in an early matter-dominated era using N-body simulations

We study the dynamics of the collapse of a nonspherical overdense patch during an early matter-dominated era and the associated production of gravitational waves (GWs) using a semirelativistic N-body framework that we develop. The collapsing patch is initialized through a Zel'dovich deformation of a homogeneous sphere and evolved in an Einstein--de Sitter background, while the emitted signal is computed directly from the numerical quadrupole evolution. We show that a reliable prediction of the signal requires a fully numerical treatment of the nonlinear collapse dynamics. In particular, fitting-based procedures and Zel'dovich-based estimates fail to capture the post-shell-crossing evolution and can over/under-estimate the emitted power of the GWs. After averaging over realizations weighted by the Doroshkevich and BBKS (peak theory) distributions, we find that the two spectra have similar shapes and remain within the same overall order of magnitude at the peak amplitude, although the BBKS result is systematically smaller. The dominant contribution arises from peaks of relatively modest height, around $ν\simeq 3$, while a larger variance significantly enhances the signal. Finally, by varying the horizon mass and reheating temperature, we map the present-day GW spectra to the sensitivity bands of different classes of detectors. In this way, the signal can populate a broad range of frequencies, from pulsar timing arrays to very high-frequency experiments, showing that GWs from nonspherical collapse can provide a probe of the pre-BBN thermal history.

astro-ph.CO↗

arXiv2026

Formation of trapped vacuum bubbles during inflation, and consequences for PBH scenarios

A class of inflationary scenarios for primordial black hole (PBH) formation include a small barrier in the slope of the potential. There, the inflaton slows down, generating an enhancement of primordial perturbations. Moreover, the background solution overcomes the barrier at a very low speed, and large backward quantum fluctuations can prevent certain regions from overshooting the barrier. This leads to localized bubbles where the field remains trapped behind the barrier. In such models, therefore, we have two distinct channels for PBH production: the standard adiabatic density perturbation channel and the bubble channel. Here, we perform numerical simulations of bubble formation, addressing the issues of initial conditions, critical amplitude and bubble expansion. Further, we explore the scaling behaviour of the co-moving size of bubbles with the initial amplitude of the field fluctuation. We find that for small to moderate non-Gaussianity $f_{\rm NL}\lesssim 2.6$, the threshold for the formation of vacuum bubbles agrees with previous analytical estimates arXiv:1908.11357 to $5\%$ accuracy or so. We also show that the mass distribution for the two channels is different, leading to a slightly broader range of PBH masses. The bubble channel is subdominant for small $f_{\rm NL}$, and becomes dominant for $f_{\rm NL}\gtrsim 2.6$. We find that the mass of PBHs in the bubble channel is determined by an adiabatic overdensity surrounding the bubble at the end of inflation. Remarkably, the profile of this overdensity turns out to be of type-II. This represents a first clear example showing that overdensities of type-II can be dominant relative to the standard type-I. We also comment on exponential tails and on the fact that in models with local type non-Gaussianity (such as the one considered here), the occurrence of alternative channels can easily be inferred from unitarity considerations.

astro-ph.CO↗

arXiv2026

Inflationary relics from an Ultra-Slow-Roll plateau

We investigate the formation of primordial black holes (PBHs) in inflationary scenarios featuring an ultra-slow-roll (USR) plateau with a sharp transition to slow roll. We focus on two coexisting production channels: PBHs originating from relic vacuum bubbles where the inflaton got trapped on the plateau, and PBHs arising from standard adiabatic density perturbations. From detailed numerical simulations we find that the bubbles are generically surrounded by type-II curvature fluctuations. Special attention is given to the distribution of initial conditions, including the relevant mean profiles and shape dispersion around them. For the adiabatic channel, we extend the logarithmic template formula $ζ[ζ_G]$, which maps the Gaussian curvature perturbation to the fully non-Gaussian one while incorporating mode evolution, and we compare this with numerical results obtained using the $δN$ formalism. While the template departs from numerical results near its logarithmic divergence, it still provides accurate threshold values for PBH formation in the parameter range relevant to our analysis. Finally, we compute the PBH mass functions for both channels. We find that the adiabatic channel dominates over the bubble-induced channel by a factor $\sim \mathcal{O}(10-10^{2})$, and that both contributions are largely dominated by the mean profiles.

astro-ph.CO↗

arXiv2025

A new approach for simulating PBH formation from generic curvature fluctuations with the Misner-Sharp formalism

Primordial Black Holes (PBHs) may have formed in the early Universe due to the collapse of super-horizon curvature fluctuations. Simulations of PBH formation have been essential for inferring the initial conditions that lead to black hole formation and for studying their properties and impact on our Universe. The Misner-Sharp formalism is commonly used as a standard approach for these simulations. Recently, type-II fluctuations, characterized by a non-monotonic areal radius, have gained interest. In the standard Misner-Sharp approach for simulating PBH formation with these fluctuations, the evolution equations exhibit divergent terms ($0/0$), which complicate and prevent the simulations. We formulate a new approach to overcome this issue in a simple manner by using the trace of the extrinsic curvature as an auxiliary variable, allowing simulations of type-II fluctuations within the Misner-Sharp formalism. Using a set of standard exponential-shaped curvature profiles, we apply and test our new approach and numerical code based on pseudospectral methods to study the time evolution of the gravitational collapse, threshold values of type A/B PBHs and PBH mass. Interestingly, we identify cases of type-II fluctuations that do not necessarily result in PBH formation.

astro-ph.CO↗

arXiv2025

Numerical simulation of type II primordial black hole formation

This study investigates the formation of type II primordial black holes (PBHs) resulting from extremely large amplitudes of initial fluctuations in a radiation-dominated universe. We find that, for a sufficiently large initial amplitude, the configuration of trapping horizons shows characteristic structure due to the existence of bifurcating trapping horizons. We call this type of configuration of the trapping horizons type II-B PBH, while the structure without a bifurcating trapping horizon type II-A PBH. In Ref. [1], in the dust-dominated universe, the type B PBH can be realized by the type II initial fluctuation, which is characterized by a non-monotonic areal radius as a function of the radial coordinate (throat structure) in contrast with the standard case, type A PBH with a monotonic areal radius (type I fluctuation). Our research reveals that a type II fluctuation does not necessarily result in a type B PBH in the radiation-dominated case. We also find that for an initial amplitude well above the threshold value, the resulting PBH mass may either increase or decrease with the initial amplitude, depending on its specific profile rather than its fluctuation type.

gr-qc↗

arXiv2025

Threshold for PBH formation in the type-II region and its analytical estimation

We numerically simulate the formation of Primordial Black Holes (PBHs) in a radiation-dominated Universe under the assumption of spherical symmetry, driven by the collapse of adiabatic fluctuations, for different curvature profiles $ζ$. Our results show that the threshold for PBH formation, defined as the peak value of the critical compaction function $\mathcal{C}_{c}(r_m)$ (where $r_m$ is the scale at which the peak occurs), does not necessarily asymptotically saturate to its maximum possible value in the type-I region for sufficiently sharp profiles. Instead, the threshold is found in the type-II region with $\mathcal{C}_{c}(r_m)$ being a minimum. We find, for the cases tested, that this is a general trend associated with profiles that exhibit extremely large curvatures in the linear component of the compaction function $\mathcal{C}_{l}(r) \equiv -4r ζ'(r)/3$ shape around its peak $r_m$ (spiky shapes). To measure this curvature at $r_m$, we define a dimensionless parameter, $κ\equiv -r^{2}_m \mathcal{C}_l''(r_m)$, and we find that the thresholds observed in the type-II region occur for sufficiently large $κ$ for the profiles we have used, contrary to expectations. By defining the threshold in terms of $\mathcal{C}_{l,c}(r_m)$, we extend previous analytical estimations to the type-II region, which is shown to be accurate within a few percent when compared to the numerical simulations for the tested profiles. Our results suggest that current PBH abundance calculations for models where the threshold lies in the type-II region may have been overestimated due to the general assumption that it should saturate at the boundary between the type-I and type-II regions.

astro-ph.CO↗

arXiv2025

Non-spherical effects on the mass function of Primordial Black Holes

In this letter, we investigate the impact of non-spherical effects on the Primordial Black Hole mass function, based on the ellipticity-dependent threshold calculated by performing $3+1$ relativistic numerical simulations. We consider an equation of state of radiation $w:=P/ρ=1/3$ and a softer one $w=1/10$ with $P$ and $ρ$ being the pressure and energy density, respectively. We suppose that the curvature perturbations obey Gaussian statistics with a monochromatic power spectrum and examine the most probable ellipsoidal configurations utilizing peak theory. We also suppose the critical scaling law of the PBH mass near the threshold following the known results. The simulations arXiv:2410.03452 show that the non-sphericity can easily prevent the system from black hole formation when the initial fluctuation amplitude is near the threshold (critical scaling regime). Nevertheless, we show that the non-spherical effects make the mass function just a few times smaller and are insignificant on the mass function distribution, including the power-law scaling in the small mass region.

gr-qc↗

arXiv2025

Simulations of Ellipsoidal Primordial Black Hole Formation

We perform $3+1$ relativistic numerical simulations to study primordial black hole (PBH) formation from the collapse of adiabatic super-horizon non-spherical perturbations generated from curvature fluctuations obeying random Gaussian statistics with a monochromatic power spectrum. The matter field is assumed to be a perfect fluid of an equation of state $w:=P/ρ={\rm const.}$ with $P$ and $ρ$ being the pressure and the energy density, respectively. The initial spatial profile of the curvature perturbation is modeled with the amplitude $μ$ and non-spherical parameters $e$ (ellipticity) and $p$ (prolateness) according to peak theory. We focus on the dynamics and the threshold for PBH formation in terms of the non-spherical parameters $e$ and $p$. We find that the critical values ($e_c, p_c$) with a fixed value of $μ$ closely follow a superellipse curve. With $p=0$, for the range of amplitudes considered, we find that the critical ellipticity for non-spherical collapse follows a decaying power law as a function of $(μ-μ_{\rm c,sp})$ with $μ_{\rm c,sp}$ being the threshold for the spherical case. Our results also indicate that, for both cases of $w = 1/3$ and $w = 1/10$, small deviations from sphericity can avoid collapsing to a black hole when the amplitude is near its critical threshold. Finally we discuss the significance of the ellipticity on the rate of the PBH production.

gr-qc↗

arXiv2025

Primordial black hole formation from a type II perturbation in the absence and presence of pressure

We investigate primordial black holes (PBHs) formed from extremely large amplitudes of primordial curvature fluctuations, classified as type II. Type II fluctuations differ from type I by the presence of a stationary point on the initial time slice, when we see the areal radius as a function of the radial coordinate. Starting from these type II perturbations to form black holes, the nonlinear evolution governed by the Einstein equations generally results in two distinct types, A and B, of horizon configurations, respectively characterized by the absence and presence of a bifurcating trapping horizon where past and future trapping horizons meet. In this paper, we use the Lemaitre-Tolman-Bondi solution to show that type I/II and type A/B classifications are equivalent for a spherically symmetric dust fluid system, regardless of the fluctuation profile. However, this equivalence does not generally hold in the presence of pressure.

gr-qc↗

arXiv2025

Primordial Black Holes

Aspects of primordial black holes, i.e. black holes formed in the early Universe, are reviewed. Special emphasis is put on their formation, their role as dark matter candidates and their manifold signatures, particularly through gravitational waves.

astro-ph.CO↗

arXiv2025

The LISA forecast on a smooth crossover beyond the Standard Model through the scalar-induced gravitational waves

Supposing the Laser Interferometer Space Antenna (LISA) gravitational wave (GW) detector, we exhibit the detectability of a hypothetical smooth crossover in the early universe beyond the Standard Model of particle physics through the scalar-induced gravitational wave (SIGW) in terms of the Fisher forecast. A crossover at $\sim100\,\mathrm{TeV}$ can leave a signal on the GW spectrum in the $\sim\mathrm{mHz}$ frequency range, the sweet spot of the LISA sensitivity. These possibilities are also interesting in the primordial black hole (PBH) context as the associated PBH mass $\sim10^{22}\,\mathrm{g}$ lies at the window to explain the whole dark matter. We found that the properties of the crossover can be well determined if the power spectrum of primordial scalar perturbations are as large as $\sim5\times10^{-4}$ on the corresponding scale $\sim10^{12}\,\mathrm{Mpc^{-1}}$.

astro-ph.CO↗

arXiv2024

Were you born in an aborted primordial black hole?

We propose a mechanism of electroweak baryogenesis based on the Standard Model and explaining the coincidence between the baryon and Dark Matter (DM) densities. Large curvature fluctuations slightly below the threshold for Primordial Black Hole (PBH) formation locally reheat the plasma above the sphaleron barrier when they collapse gravitationally, leading to regions with a maximal baryogenesis at the Quantum Chromodynamics epoch. Using numerical relativity simulations, we calculate the overdensity threshold for baryogenesis. If PBH significantly contribute to the DM, aborted PBHs can generate a baryon density and an averaged baryon-to-photon ratio consistent with observations.

astro-ph.CO↗

arXiv2024

Primordial Black Holes and Induced Gravitational Waves from a Smooth Crossover beyond Standard Model

Gravitational waves (GWs) induced by primordial fluctuations can be affected by the modification of the sound speed $c^2_{\rm s}$ and the equation of state parameter $w$ once the curvature fluctuations reenter the cosmological horizon. That softening can also significantly boost the production of Primordial Black Holes (PBHs) at the mass scale where the softening arises. In this work, we consider a hypothetical softening of $w$ and $c^2_{\rm s}$ caused by a smooth crossover beyond Standard Model theories, for what we numerically compute the secondary induced GW considering the case of a flat scale-invariant power spectrum. We find that if the amplitude of the power spectrum is sufficiently large, the characteristic feature of the GW signal caused by the smooth crossover can be detected by future space-based gravitational wave interferometers and differentiated from the pure radiation case. At the same time, depending on the mass scale where the crossover occurs, such a scenario can have compatibility with PBHs being all the dark matter when $\mathcal{A} \sim \mathcal{O}(10^{-3})$, with a mass function very sharply peaked around the horizon mass scale of the minimum of the sound speed. Our results show that the GW signal can be used to resolve the existing degeneracy of sharply peaked mass function caused by peaked power spectrums and broad ones in the presence of softenings of $w$ and $c^2_{\rm s}$.

astro-ph.CO↗