Article
Astronomy & Astrophysics
Tingqi Cai, Jie Jiang, Yi Wang
Summary: This study presents the first lattice simulation to investigate the nature of multi-stream inflation. The simulation confirms the physical picture of multi-stream inflation and reveals new findings in parameter space and field behaviors. It shows that gradient energy plays a significant role in multi-stream inflation. The bifurcation probability in a double field potential with a shifted Gaussian barrier is controlled by the shift distance with an error function relation. The bubbles created by bifurcation tend to be more spherical as bifurcation probability decreases. Furthermore, bifurcation is more likely to introduce oscillations of field values inside the bubbles than outside.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Astronomy & Astrophysics
Jason Kristiano, Jun'ichi Yokoyama
Summary: By calculating the one-loop correction to the two-point functions of curvature perturbation in single-field inflation generated by cubic self-interaction, we find that the correction is finite and inversely proportional to the spectral tilt. Requiring the correction to be much smaller than the tree-level contribution leads to an upper bound on primordial non-Gaussianity. Observationally, the allowed region of non-Gaussian parameter space is entirely included by the region where the one-loop correction is smaller than the tree-level contribution, but there exists a significantly large region where the one-loop correction is larger than 1% or even 10% of the latter. If future observations confirm non-Gaussianity falling within such a region, it would be important to incorporate higher-order corrections to the spectrum in order to achieve precise cosmology. In some extreme cases, where the one-loop correction has a comparable magnitude to the tree-level contribution, it might indicate a breakdown of the cosmological perturbation theory in the context of single-field inflation.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Astronomy & Astrophysics
Guido D'Amico, Nemanja Kaloper
Summary: Inflation does not have to occur all at once, and can be solved by a series of short bursts of cosmic acceleration interrupted by brief periods of decelerated expansion. This allows for more flexibility in theory and can lead to interesting predictions regarding scalar and tensor spectra of perturbations at short wavelengths. Future CMB spectroscopy searches and primordial gravity probes may help test these features and reveal potential populations of rare particles or primordial black holes as dark matter.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Astronomy & Astrophysics
Fengge Zhang, Yungui Gong, Jiong Lin, Yizhou Lu, Zhu Yi
Summary: The study of non-Gaussianities of primordial curvature perturbations in G-inflation models reveals that even though f(NL) becomes large at certain scales, it remains to be small at peak scales. This suggests that the contributions of non-Gaussianity to scalar induced secondary gravitational waves and primordial black hole abundance are expected to be negligible.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Astronomy & Astrophysics
Jinn-Ouk Gong, Maria Mylova
Summary: In this study, we examine the validity of the classical approximation of the waterfall phase transition in hybrid inflation from an effective field theory perspective. By integrating out the fluctuations of the waterfall field up to one-loop order, an effective field theory is constructed. Assuming slow-roll conditions are satisfied, we find that the backreaction of the waterfall field fluctuations can significantly impact the evolution of the system, rendering the classical approximation invalid. We derive the necessary constraint to ensure the validity of the effective field theory.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Astronomy & Astrophysics
Markus B. Froeb, William C. C. Lima
Summary: We introduce a recent approach to construct gauge-invariant relational observables in gravity within the framework of cosmological perturbation theory. These observables are built using a field-dependent coordinate system, specifically geodesic lightcone coordinates. We demonstrate that these observables are gauge-independent in the fully nonlinear theory and take the expected form when the geodesic lightcone gauge for the metric is adopted. Explicit expressions for the Sasaki-Mukhanov variable at linear order and the Hubble rate, as measured by both geodesic and inflaton co-moving observers, to second order are provided. Furthermore, we show that the well-known linearized equations of motion for the Sasaki-Mukhanov variable and the scalar constraint variables are derived from the gauge-invariant Einstein's equations.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Astronomy & Astrophysics
Harry Goodhew, Sadra Jazayeri, Mang Hei Gordon Lee, Enrico Pajer
Summary: This paper discusses the initial conditions of the universe and the impact of quantum mechanics on late-time observables, deriving a set of single-cut rules, discussing the analytical structure of the wave function, and verifying the applicability of these rules in some specific examples.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Astronomy & Astrophysics
Arunoday Sarkar, Chitrak Sarkar, Buddhadeb Ghosh
Summary: By defining the k-modes of quantum fluctuations during inflation through the dynamical horizon crossing condition k = aH, and solving the equations of cosmological first-order perturbations self-consistently with chaotic alpha-attractor type potentials, we were able to study the behavior of various parameters in k-space. Comparison with Planck data in the low-k regime constrained the values of the alpha parameter through microscopic calculations. The calculated results matched the Planck-2018 data with 68% or near 95% CL for various values of alpha.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Astronomy & Astrophysics
Mohammad Ali Gorji, Hayato Motohashi, Shinji Mukohyama
Summary: We investigate a novel single field inflationary scenario that allows a transition from slow-roll inflation to ghost inflation, achieved through smoothly unifying the two phases with the introduction of a higher derivative scordatura term. The model avoids strong coupling and gradient instability and provides a self-consistent approach to accessing ghost inflation.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Astronomy & Astrophysics
Matteo Braglia, Xingang Chen, Dhiraj Kumar Hazra
Summary: This paper introduces a methodology for directly comparing numerical predictions from complicated multi-field feature models with Planck data using a complete model of classical primordial standard clocks as an example. Although no statistically significant candidates were found, this methodology can facilitate future research on primordial features and data analysis, providing a framework for further testing with upcoming cosmic microwave background polarization observations and galaxy surveys.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Astronomy & Astrophysics
Manuel Alejandro Jaramillo Rodrguez, Antonio Enea Romano, Sergio Andres Vallejo-Pena
Summary: This study analyzes the effects of a momentum dependent effective sound speed (MESS) on cosmic microwave background (CMB) data, showing a significant improvement in fit compared to models without MESS. The research suggests that primordial entropy perturbations could explain deviations observed in the curvature perturbation spectrum.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Astronomy & Astrophysics
Amjad Ashoorioon, Ghazal Geshnizjani, Hyung J. Kim
Summary: In this paper, we study the validity and non-Gaussianity of Extended Effective Field Theory of Inflation (EEFToI) with initial conditions set with dispersion relations omega(2) a k(6). By computing the bispectrum and investigating the shape of triangles, we find interesting regions of parameter space where EEFToI with these initial conditions is sensible.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Astronomy & Astrophysics
Nicola Bartolo, Giovanni Battista Carollo, Sabino Matarrese, Luigi Pilo, Rocco Rollo
Summary: “We analyze the physical content of squeezed bispectra involving long-wavelength tensor perturbations and show that these modes cannot be gauged away, except in the unphysical limit of infinite wavelength, k = 0. This result has a direct implication on the validity of the Maldacena consistency relation, which is respected by a subclass of inflationary models. Consequently, future experiments can observe squeezed mixed correlators in the squeezed limit, similar to the scalar-scalar-scalar bispectrum, and they remain a key channel to study Early Universe physics and discriminate among different models of inflation.”
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Astronomy & Astrophysics
Keisuke Inomata, Evan McDonough, Wayne Hu
Summary: Future experiments on cosmic microwave background, gravitational wave, and large scale structure will allow us to study the primordial power spectrum on small scales, potentially revealing the mechanisms and correlations behind the formation of primordial black holes.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Astronomy & Astrophysics
Yuichiro Tada, Vincent Vennin
Summary: This study presents a generic framework to compute the one-point statistics of cosmological perturbations at an arbitrary scale, considering the presence of quantum diffusion. The study derives explicit formulae for the probability density function of the curvature perturbation, the comoving density contrast, and the compaction function. The framework is applied to calculate the mass distribution of primordial black holes and confirms the heavy-tailed distribution and the impact of stochastic contamination effects.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Astronomy & Astrophysics
Yashar Akrami, Misao Sasaki, Adam R. Solomon, Valeri Vardanyan
Summary: Models of dark energy with multiple fields are theoretically motivated and predict distinct observational signatures, potentially addressing issues present in standard single-field dark energy. While these multi-field models may appear similar to concordance cosmology at the background level, dark energy perturbations can cluster and enhance the growth of large-scale structure, which may be testable in future cosmological surveys.
Article
Astronomy & Astrophysics
A. Banerjee, E. O. Colgain, M. Sasaki, M. M. Sheikh-Jabbari, T. Yang
Summary: Quasars show potential as standard candles at high redshifts beyond Type Ia supernovae. Recent research has found that the Hubble diagram of quasars matches the standard flat Lambda CDM model up to z around 1.5-2, but deviates at higher redshifts. The reliability of the polynomial expansion for luminosity distance may only be trusted up to around z 1.5-2.
Article
Physics, Particles & Fields
Borna Salehian, Hong-Yi Zhang, Mustafa A. Amin, David Kaiser, Mohammad Hossein Namjoo
Summary: This paper systematically derives the SP equations and relativistic corrections from the nonlinear and fully relativistic KGE equations in an expanding universe, providing insights into deviations and applicability beyond the SP system. The method presented simplifies the analysis of scalar dark matter dynamics and accurately captures deviations from the SP system towards the full KGE case, particularly in calculating the mass-radius relationship of solitons.
JOURNAL OF HIGH ENERGY PHYSICS
(2021)
Article
Physics, Multidisciplinary
Yi-Fu Cai, Jie Jiang, Misao Sasaki, Valeri Vardanyan, Zihan Zhou
Summary: The proposed mechanism enhances primordial gravitational waves without affecting curvature perturbations during inflation, providing a new perspective for detectable inflationary tensor modes with low-scale inflation. This mechanism can be tested with upcoming cosmic microwave background B-mode observations.
PHYSICAL REVIEW LETTERS
(2021)
Article
Astronomy & Astrophysics
Guillem Domenech, Volodymyr Takhistov, Misao Sasaki
Summary: Primordial black holes from the early Universe can significantly affect cosmological history. Exploring the formation mechanisms of these black holes can be done through coincidental dark radiation and density fluctuation gravitational wave signatures.
Article
Philosophy
Feraz Azhar, Alan H. Guth, Mohammad Hossein Namjoo
Summary: This article discusses Adam Elga's principle of indifference for self-locating beliefs and uses a Bayesian approach to argue against Elga's circular reasoning.
Article
Astronomy & Astrophysics
Sina Hooshangi, Mohammad Hossein Namjoo, Mahdiyar Noorbala
Summary: This paper investigates the limitations of perturbative treatment in predicting the abundance of primordial black holes (PBHs) and proposes a nonperturbative estimation method, called the SN formalism, for the tail of the probability distribution function (PDF). The results show that the SN formalism can provide more accurate predictions on the tail behavior, leading to a significant enhancement of PBH formation probability compared to perturbation theory.
Correction
Philosophy
Feraz Azhar, Alan H. Guth, Mohammad Hossein Namjoo
Article
Astronomy & Astrophysics
Guillem Domenech, Misao Sasaki
Summary: The end state of Hawking evaporation of a black hole is uncertain. Some quantum gravity theories suggest the existence of Planck sized remnants, such as loop quantum gravity and asymptotic safe gravity. If this is the case, the Universe might be filled with remnants of tiny primordial black holes, formed with mass M<109 M & SIM; 5x105.
CLASSICAL AND QUANTUM GRAVITY
(2023)
Article
Astronomy & Astrophysics
Sina Hooshangi, Alireza Talebian, Mohammad Hossein Namjoo, Hassan Firouzjahi
Summary: We study the effects of curvature perturbations and non-Gaussianities in a model of two-field ultraslow-roll inflation bounded by a curve in the field space. We find that the abundance of primordial black holes can be significantly enhanced by nonlinear effects. The probability distribution function for curvature perturbation is sensitive to the geometry of the boundary.
Article
Astronomy & Astrophysics
Chul-Moon Yoo, Tomohiro Harada, Shin'ichi Hirano, Hirotada Okawa, Misao Sasaki
Summary: In this study, we numerically investigate the formation of primordial black holes (PBHs) caused by an isocurvature perturbation in the radiation-dominated Universe. Our simulations of spherically symmetric configurations show that a PBH is formed if the amplitude of the scalar field profile is sufficiently large. However, we find that the late-time behavior of the gravitational collapse is dominated by the dynamics of the fluid, rather than the scalar field.
Article
Astronomy & Astrophysics
Guillem Domenech, Misao Sasaki
Summary: This paper discusses the gauge dependence issue of induced gravitational wave spectrum in cosmological backgrounds, providing simple formulas and highlighting the difference between observable quantities and gauge-invariant variables. It suggests that the Newton gauge is suitable for calculations and interpretations of induced gravitational waves, and shows that the spectrum remains invariant under reasonable gauge transformations when the source term becomes inactive.
Article
Astronomy & Astrophysics
Zihan Zhou, Jie Jiang, Yi-Fu Cai, Misao Sasaki, Shi Pi
Article
Physics, Multidisciplinary
Alexander Kusenko, Misao Sasaki, Sunao Sugiyama, Masahiro Takada, Volodymyr Takhistov, Edoardo Vitagliano
PHYSICAL REVIEW LETTERS
(2020)
Article
Astronomy & Astrophysics
Rong-Gen Cai, Shi Pi, Misao Sasaki
