Article
Astronomy & Astrophysics
Masahiro Kawasaki, Kai Murai, Hiromasa Nakatsuka
Summary: The study found that primordial black holes (PBHs) formed by Affleck-Dine (AD) baryogenesis exhibit strong clustering at formation, which is important for estimating their merger rates. Taking clustering into account, the evaluation of the PBH merger rate and isocurvature perturbations show significant deviations from those without clustering.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Astronomy & Astrophysics
Milad Solbi, Kayoomars Karami
Summary: Recent observational constraints suggest that primordial black holes with mass scale similar to 10(-12) solar masses can account for most of the dark matter in the Universe. Through studying a specific inflation model, it has been found that the model can generate primordial black holes with mass scale around 10(-13) solar masses and high abundance of 0.96 under certain parameter values. Additionally, the energy density parameter of induced gravitational waves behaves as a power-law function in the infrared limit.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Astronomy & Astrophysics
G. Rigopoulos, A. Wilkins
Summary: In this study, the Hamilton-Jacobi formulation of stochastic inflation is applied to describe the evolution of the inflaton during Ultra-Slow Roll, emphasizing the impact of the field's velocity and gravitational backreaction. The calculation of the mass fraction of Primordial Black Holes formed by a plateau in the inflationary potential reveals potential issues with overproduction due to the inflaton velocity before reaching zero. This suggests that the evolution of the inflaton is predominantly classical, with diffusion effects being subdominant.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Astronomy & Astrophysics
Lilia Anguelova
Summary: In this study, rapid-turn trajectories in a class of two-field cosmological models are investigated, showing that certain solutions can induce primordial black hole formation through a transient rapid-turn period. By relaxing the symmetry condition, modified solutions were found with improved behavior of the Hubble eta-parameter, including a brief ultra-slow roll phase followed by long-term slow roll inflation. Slow roll was observed near the center of the Poincare disk, in contrast to the standard alpha-attractor case.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Astronomy & Astrophysics
Marco Taoso, Alfredo Urbano
Summary: The study analyzes the impact of primordial non-gaussianities in the presence of an ultra-slow phase during inflationary dynamics, focusing on scenarios relevant for the production of primordial black holes. By computing the three-point correlation function of comoving curvature perturbations, it is found that non-gaussianities are significant and mainly local, affecting the estimated abundance of primordial black holes obtained with the Gaussian approximation. However, it is shown that this effect can be compensated by slightly adjusting the amplitude of the primordial power spectrum of curvature perturbations through a small tuning of the parameters of the inflationary model.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Astronomy & Astrophysics
Jacopo Fumagalli, Sebastien Renaux-Petel, John W. Ronayne, Lukas T. Witkowski
Summary: We propose a new mechanism for producing primordial black holes during a period of multi-field inflation. This mechanism requires an enhancement of primordial fluctuations at short scales compared to those at CMB scales. We show that this amplification naturally occurs when the inflationary trajectory deviates strongly from a geodesic in field space, and can subsequently produce enough primordial black holes to account for all or a fraction of dark matter. Our mechanism is applicable to inflation models in a multi-dimensional field space, as occurs in high-energy theories. We analytically and numerically study how the duration and strength of the trajectory deviation affect the primordial fluctuation power spectrum and the abundance of primordial black holes. Our mechanism offers valuable insights into the dynamics of inflation through observable features in the primordial black hole spectrum and the stochastic background of gravitational waves.
Article
Astronomy & Astrophysics
Matthew W. Davies, Pedro Carrilho, David J. Mulryne
Summary: In this study, we work within an idealized framework to match a series of evolution phases defined by the second slow-roll parameter eta. We calculate the reduced bispectrum, f(NL), for inflation models with a significant peak in their primordial power spectra. Our findings show that f(NL) remains relatively constant over the scales where the peak is located, and we provide an analytic approximation for this value. Additionally, we identify the conditions under which f(NL) is large enough to have a significant impact on the production of primordial black holes (PBHs) and scalar induced gravitational waves (SIGWs). The analytic formulas for the gradient of the rise and fall in the power spectrum, along with these findings, offer a toolkit for designing or quickly analyzing inflationary models that generate PBHs and SIGWs.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Astronomy & Astrophysics
Jessica L. Cook
Summary: This paper considers the formation of primordial black holes (PBHs) sourced by an increase in the power spectrum. Two background inflaton models, natural inflation and hilltop inflation, are examined. Instead of a peaked power spectrum, this paper explores the formation of PBHs from perturbations closer to the end of inflation, ensuring that the PBHs are too small to violate bounds. Understanding PBHs sourced from an inflationary power spectrum would provide valuable evidence for inflation on a different energy scale from the cosmic microwave background (CMB), shedding light on what occurred during inflation.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2023)
Article
Astronomy & Astrophysics
Chiara Animali, Vincent Vennin
Summary: In this work, we study cosmological fluctuations and the formation of Primordial Black Holes (PBHs) through the process of stochastic tunneling, where the inflaton escapes a local minimum of its potential through quantum fluctuations. We analyze two different toy models and find that when the potential barrier is small enough compared to its width, the potential can be approximated as flat and PBHs are not massively produced. However, when the potential barrier height exceeds a certain critical value, the PBH abundance grows exponentially or even super-exponentially.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2023)
Article
Astronomy & Astrophysics
Chengjie Fu, Chao Chen
Summary: We investigate the amplification of curvature perturbations in a two-field inflation model featuring a Gaussian potential bump. When the inflaton encounters a potential bump along the inflationary trajectory, its rolling speed is generally reduced, potentially causing a violation of the slow-roll condition. Our paper offers a simple example of the extension of a bump-like potential for primordial black hole (PBH) formation from single-field inflation to a two-field case, which helps alleviate the fine-tuning of initial conditions to some extent.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2023)
Article
Astronomy & Astrophysics
Matteo Braglia, Andrei Linde, Renata Kallosh, Fabio Finelli
Summary: We explore the two-stage inflation regime in the hybrid cosmological alpha-attractors theory. The inflationary perturbations spectrum is consistent with the latest Planck/BICEP/Keck Array results due to the attractor properties of the model. However, at smaller scales, there may be a highly controllable peak of considerable width and position, which can lead to the abundant production of primordial black holes (PBH) and the generation of a stochastic background of gravitational waves (SGWB).
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2023)
Article
Astronomy & Astrophysics
Soma Heydari, Kayoomars Karami
Summary: This study investigates the creation of primordial black holes (PBHs) through the nonminimal coupling between gravity and field derivative setup. By fine-tuning the model parameters, the evolution of the inflaton field is slowed down, leading to enhanced curvature perturbations. The study also examines the production of PBHs with different masses and the resulting gravitational waves, finding that the density parameter spectra of gravitational waves for all cases are within the sensitivity ranges of gravitational wave detectors.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Astronomy & Astrophysics
Theodoros Papanikolaou, Andreas Lymperis, Smaragda Lola, Emmanuel N. Saridakis
Summary: Primordial black holes (PBHs) can be formed through non-canonical inflation, and can provide observational evidence of the early Universe. Constraints on the non-canonical exponents are extracted by requiring significant PBH production. Asteroid-mass PBHs can explain the dark matter, and solar-mass PBHs within the LIGO-VIRGO detection band can be produced. The collapse of enhanced cosmological perturbations that form PBHs can also generate a detectable stochastic gravitational wave (GW) background.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2023)
Review
Astronomy & Astrophysics
Ogan Ozsoy, Gianmassimo Tasinato
Summary: We review the conceptual aspects of inflationary scenarios that can lead to the formation of primordial black holes by amplifying the size of curvature fluctuations. Various mechanisms are identified for both single-field and multiple-field inflation. In single-field inflation, the enhancement of curvature fluctuations occurs through non-slow-roll inflationary evolution induced by pronounced gradients of background quantities. In multiple-field inflation, amplification is achieved through appropriate couplings with additional sectors characterized by tachyonic instabilities.
Article
Astronomy & Astrophysics
Mar Bastero-Gil, Marta Subias Diaz-Blanco
Summary: Research shows that in some warm inflation models, interactions with other light degrees of freedom can enhance the primordial spectrum during the final stages of inflation and lead to the formation of evaporating Primordial Black Holes. These fluctuations also act as a source for tensors at second order and peak near the end of inflation, resulting in a spectral density of Gravitational Waves with frequencies around O(10^5 - 10^6) Hz and an amplitude of around 10^-9.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)