arXiv subjects

Albert Escrivà

Publications and source records attributed to Albert Escrivà.

31 records · Page 2Linked to original sources

arXiv2024

Primordial Black Hole formation from overlapping cosmological fluctuations

We consider the formation of primordial black holes (PBHs), during the radiation-dominated Universe, generated from the collapse of super-horizon curvature fluctuations that are overlapped with others on larger scales. Using a set of different curvature profiles, we show that the threshold for PBH formation (defined as the critical peak of the compaction function) can be decreased by several percentages, thanks to the overlapping between two peaks in the profile of the compaction function. In the opposite case, when the fluctuations are sufficiently decoupled the threshold values behave as having the fluctuations isolated (isolated peaks). We find that the analytical estimates of arXiv:1907.13311 can be used accurately when applied to the corresponding peak that is leading to the gravitational collapse. We also study in detail the dynamics and estimate the final PBH mass for different initial configurations, showing that the profile dependence has a significant effect on that.

gr-qc↗

arXiv2023

Primordial Black Hole Formation during a Strongly Coupled Crossover

The final mass distribution of primordial black holes is sensitive to the equation of state of the Universe at the scales accessible by the power spectrum. Motivated by the presence of phase transitions in several beyond the Standard Model theories, some of which are strongly coupled, we analyze the production of primordial black holes during such phase transitions, which we model using the gauge/gravity duality. We focus in the (often regarded as physically uninteresting) case for which the phase transition is just a smooth crossover. We find an enhancement of primordial black hole production in the range $M_{\rm{PBH}}\in[10^{-16},10^{-6}]M_{\odot}$.

astro-ph.CO↗

arXiv2022

Simulations of PBH formation at the QCD epoch and comparison with the GWTC-3 catalog

The probability of primordial black hole (PBH) formation is known to be boosted during the Quantum Chromodynamics (QCD) crossover due to a slight reduction of the equation of state. This induces a high peak and other features in the PBH mass distribution. But the impact of this variation during the PBH formation has been so far neglected. In this work we simulate for the first time the formation of PBHs by taking into account the varying equation of state at the QCD epoch, compute the over-density threshold using different curvature profiles and find that the resulting PBH mass distributions are significantly impacted. The expected merger rate distributions of early and late PBH binaries is comparable to the ones inferred from the GWTC-3 catalog for dark matter fractions in PBHs within $0.1 < f_{\rm PBH} <1 $. The distribution of gravitational-wave events estimated from the volume sensitivity could explain mergers around $30-50 M_\odot$, with asymmetric masses like GW190814, or in the pair-instability mass gap like GW190521. However, none of the considered cases leads to a multi-modal distribution with a secondary peak around $8-15 M_\odot$, as suggested by the GWTC-3 catalog, possibly pointing to a mixed population of astrophysical and primordial black holes.

astro-ph.CO↗

arXiv2022

Simulation of Primordial Black Holes with large negative non-Gaussianity

In this work, we have performed numerical simulations of primordial black hole (PBH) formation in the Friedman-Lemaître-Robertson-Walker universe filled by radiation fluid, introducing the local-type non-Gaussianity to the primordial curvature fluctuation. We have compared the numerical results from simulations with previous analytical estimations on the threshold value for PBH formation done in the previous paper arXiv:2109.00791, particularly for negative values of the non-linearity parameter $f_{\rm NL}$. Our numerical results show the existence of PBH formation of (the so-called) type I also in the case $f_{\rm NL} \lesssim -0.336$, which was not found in the previous analytical expectations using the critical averaged compaction function. In particular, although the universal value for the averaged critical compaction function $\bar{\mathcal{C}}_{c}=2/5$ found previously in the literature is not satisfied for all the profiles considered in this work, an alternative direct analytical estimate has been found to be roughly accurate to estimate the thresholds, which gives the value of the critical averaged density with a few $\%$ deviation from the numerical one for $f_{\rm NL}\gtrsim -1$.

astro-ph.CO↗

arXiv2022

PBH formation from spherically symmetric hydrodynamical perturbations: a review

Primordial black holes, which could have been formed in the very early Universe due to the collapse of large curvature fluctuations, are nowadays one of the most attractive and fascinating research areas in cosmology for their possible theoretical and observational implications. This review article presents the current results and developments on the conditions for primordial black hole formation from the collapse of curvature fluctuations in spherical symmetry on a Friedman-Lemaitre-Robertson-Walker background and its numerical simulation. We review the appropriate formalism for the conditions of primordial black hole formation, and we detail a numerical implementation. We then focus on different results regarding the threshold and the black hole mass using different sets of curvature fluctuations. Finally, we present the current state of analytical estimations for the primordial black hole formation threshold, contrasted with numerical simulations.

gr-qc↗

arXiv2021

Static properties of two linearly coupled discrete circuits

Bosonic two-ring ladders constitute an important class of atomtronic circuits, where coherent current flows not only can offer a new insight into many-body physics, but also can play the role of actual degrees of freedom, and hence allow for a viable implementation of cold-atom based devices and qubit systems. In this work, we exhaustively investigate the ground state properties and the low-lying energy spectrum of two linearly coupled Bose-Hubbard rings. We show that the competition among interactions, intra- and inter-ring hopping processes gives place to a rather rich physical scenario, where Mott-like states and (different kinds of) superfluid-like states emerge. The latter ones depend also on the (in)commensurate filling of the atoms. Our analysis, carried out within a simple analytical framework and by means of the exact numerical diagonalization of the system Hamiltonian, provides one with a rather complete characterization of the static properties of the two-ring ladder, including, but not limited to, coherence, fragmentation, correlations, and entanglement. We complement our investigation by studying how these indicators depend on the commensurability of the total number of bosons with respect to the total number of sites and show that the two stacked rings are always entangled for an odd number of atoms.

cond-mat.quant-gas↗

arXiv2021

Effects of the shape of curvature peaks on the size of primordial black holes

We simulate numerically the formation of spherically symmetric primordial black holes (PBHs) seeded by different families of primordial curvature perturbations profiles on a Friedman-Robertson-Walker (FRW) Universe filled by radiation fluid. We have studied the dependency on the curvature profile of the initial mass $M_{\rm BH,i}$ of the PBHs at the time of apparent horizon formation $t_{AH}$, and the final mass $M_{\rm BH,f}$ after the accretion process, using an excision technique, comparing $M_{\rm BH,i}$ to previous analytical estimations obtained using compensated PBHs model approach. The analytical estimations are in agreement with numerical results, except for large values of the initial perturbation amplitude, when the compensated model is less accurate. The masses $M_{\rm BH,f}$ and $M_{\rm BH,i}$ do not depend only on the shape around the compaction function peak, but on the full profile of the initial curvature perturbation. We also estimate the accretion effects, and for those PBHs with masses relevant for the dark matter abundance, with a final mass equal to the horizon crossing mass, we find $M_{\rm BH,f}\approx 3 M_{\rm BH,i} $.

gr-qc↗

arXiv2020

Analytical thresholds for black hole formation in general cosmological backgrounds

We consider black holes which form from an initially spherically symmetric super-Hubble perturbation of a cosmological background filled by a perfect fluid $p=w ρ$ with $w\in (0,1]$. Previous work has shown that when $w = 1/3$ (radiation), there is a critical threshold for black hole formation ($δ_c$), which, to a very good approximation, only depends upon the curvature of the compaction function around its peak value. We find that this generalizes to all $w\gtrsim 1/3$; for smaller $w$s the knowledge of the full shape of the compaction function is necessary. We provide analytic approximations for $δ_c$ which are accurate for $w\in [1/3,1]$.

gr-qc↗

arXiv2020

Tunneling vortex dynamics in linearly coupled Bose-Hubbard rings

The quantum dynamics of population-balanced fractional vortices and population-imbalanced vortices in an effective two-state bosonic system, made of two coupled discrete circuits with few sites, is addressed within the Bose-Hubbard model. % We show that for low on-site interaction, the tunneling of quantized vortices between the rings performs a coherent, oscillating dynamics connecting current states with chiral symmetry. The vortex-flux transfer dually follows the usual sinusoidal particle current of the Josephson effect, in good agreement with a mean-field approximation. Within such regime, the switch of persistent currents in the rings resembles flux-qubit features, and is feasible to experimental realization. On the contrary, strong interatomic interactions suppress the chiral current and lead the system into fragmented condensation.

cond-mat.quant-gas↗

arXiv2020

A universal threshold for primordial black hole formation

In this letter, we argue and show numerically that the threshold to form primordial black holes from an initial spherically symmetric perturbation is, to an excellent approximation, universal, whenever given in terms of the compaction function averaged over a sphere of radius $r_m$, where $r_m$ is the scale on which the compaction function is maximum. This can be understood as the requirement that, for a black hole to form, each shell of the averaged compaction function should have an amplitude exceeding the so-called Harada-Yoo-Kohri limit. For a radiation dominated universe we argued, supported by the numerical simulations, that this limit is $δ_c = 0.40$, which is slightly below the one quoted in the literature. Additionally, we show that the profile dependence of the threshold for the compaction function is only sensitive to its curvature at the maximum. We use these results to provide an analytic formula for the threshold amplitude of the compaction function at its maximum in terms of the normalised compaction function curvature at $r_m$.

gr-qc↗

arXiv2020

Simulation of primordial black hole formation using pseudo-spectral methods

In this work we have used for the first time pseudo-spectral methods to perform numerical simulations of spherically symmetric black hole formations on a Friedman-Robertson-Walker universe. With these methods, the differential equations describing the gravitational collapse are partially solved algebraically. With our publicly available code we then independently check, and confirm, previous numerical estimations of the thresholds to form primordial black holes. By using an excision technique and analytical estimations of accretion rates, we were also able to estimate the black holes mass even in the case of large deviations from the threshold. There, we confirm, with an explicit example, that the estimation of the black hole mass via the self-similar scaling law is only accurate up to $O(15\%)$, for the largest allowed mass.

gr-qc↗

arXiv2019

PBH in single field inflation: the effect of shape dispersion and non-Gaussianities

Primordial black holes (PBHs) may result from high peaks in a random field of cosmological perturbations. In single field inflationary models, such perturbations can be seeded as the inflaton overshoots a small barrier on its way down the potential. PBHs are then produced through two distinct mechanisms, during the radiation era. The first one is the familiar collapse of large adiabatic overdensities. The second one is the collapse induced by relic bubbles where the inflaton field is trapped in a false vacuum, due to large backward fluctuations which prevented horizon sized regions from overshooting the barrier. We consider (numerically and analytically) the effect of non-Gaussianities on the threshold for overdensities to collapse into a PBH. Since typical high peaks have some dispersion in their shape or profile, we also consider the effect of such dispersion on the corresponding threshold for collapse. With these results we estimate the most likely channel for PBH production as a function of the non-Gaussianity parameter $f_{\rm NL}$. We also compare the threshold for collapse coming from the perturbative versus the non perturbative template for the non-Gaussianity arising in this model. We show that i) for $f_{\rm NL}\gtrsim 3.5$, the population of PBH coming from false vacuum regions dominates over that which comes from the collapse of large adiabatic overdensities, ii) the non-perturbative template of the non-Gaussianities is important to get accurate results. iii) the effect of the dispersion is small in determining the threshold for the compaction function, although it can be appreciable in determining the threshold amplitude for the curvature perturbation at low $f_{\rm NL}$. We also confirm that the volume averaged compaction function provides a very accurate universal estimator for the threshold.

astro-ph.CO↗

arXiv2017

Beyond dimensional analysis: Higgs and new Higgs inflations {\it do not} violate unitarity

Naïve dimensional analysis seems to suggest possible unitarity violations in the framework of the Higgs and new Higgs inflationary scenarios. These violations seem to happen around the value in which the potential energy, per given Higgs boson's vacuum expectation value, crosses the perturbative cut-off scale calculated around the electroweak vacuum. Conversely to these expectations, in this paper we show that, by using an exact analysis of the background dependent cut-off scale, and by including the contribution of the phase-space volume in the perturbative scattering amplitudes, no violation of (perturbative) unitarity might ever happen during the whole Universe evolution.

hep-ph↗