Article
Astronomy & Astrophysics
Emanuela Dimastrogiovanni, Matteo Fasiello, A. Emir Gumrukcuoglu
Summary: This paper investigates the possibility of extra spinning particles during inflation, focusing on the spin-2 case. The study explores the parameter space of the inflationary Lagrangian and identifies regions with signatures detectable by upcoming CMB probes. The analysis reveals the presence of a local-type non-Gaussianity in the gravitational wave spectrum and three-point function, which may be within the sensitivity range of both LiteBIRD and CMB-S4 experiments.
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
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
Sabino Matarrese, Luigi Pilo, Rocco Rollo
Summary: By carefully implementing gauge transformations involving long-wavelength modes, it is shown that effects involving squeezed bispectrum configurations cannot be gauged away, except for the unphysical exactly infinite-wavelength limit. This result is particularly relevant for the Maldacena consistency relation for single-field inflation and the f(NL)(GR) = -5/3 term appearing in dark matter bispectrum and halo bias, indicating their physical and observable nature in principle.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
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
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
Lucas Pinol
Summary: This article explores linear dynamics and cubic interactions for N-field scalar fields during inflation, using observable curvature perturbations and entropic fluctuations. It reveals rich geometrical effects beyond scalar curvature, particularly when the field space dimension is larger than two. The article also highlights potential instability in background dynamics when N-field is greater than or equal to 3, due to negative eigenvalues in the entropic mass matrix from fast rotation of local entropic basis.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Astronomy & Astrophysics
Christopher S. Gallagher, Timothy Clifton, Chris Clarkson
Summary: Two-parameter perturbation theory is a framework designed to study the relativistic gravitational effects of small-scale nonlinear structures on the large-scale properties of the Universe. The approach in this paper uses Newtonian perturbation theory to model the gravitational fields of quasi-nonlinear structures and then applies them as source terms for large-scale cosmological perturbations. This work represents a first step towards deploying a formalism that can simultaneously model the weak gravitational fields of both linear and nonlinear structures in a realistic model of the Universe.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Astronomy & Astrophysics
Enrico Pajer
Summary: The study focuses on the three-point correlators of gravitons and scalar curvature perturbations around a quasi de Sitter space-time and establishes Bootstrap Rules that fully fix the form of these correlators in the asymptotic future at the boundary. The Boostless Bootstrap approach is shown to account for the breaking of de Sitter boosts caused by inflationary backgrounds. Derivations of bispectra involving gravitons in single-clock, canonical inflation are easily derived in this approach, as well as the scalar bispectrum in the Effective Field Theory of inflation to any order in derivatives. In many cases, the derivations are computationally simpler than the corresponding explicit calculations, emphasizing the implications of locality, vacuum choice, and underlying symmetries.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Astronomy & Astrophysics
Raphal van Laak, Sam Young
Summary: Primordial black holes are black holes that may have formed in high density regions in the early universe. The fluctuations in their formation rate can be used to constrain the amplitude of non-Gaussianity, especially if primordial black holes make up a significant fraction of dark matter. By extending the calculation to include peaks theory and considering the non-linearities between compaction C and curvature perturbation C, we find that the constraints on quadratic models of non-Gaussianity are largely unchanged, while the constraints on cubic models significantly worsen. If all of the dark matter is composed of primordial black holes, the parameters of non-Gaussianity are -2.9 & BULL; 10-4 < f < 3.8 & BULL; 10-4 and -1.5 & BULL; 10-3 < g < 1.9 & BULL; 10-3 for quadratic and cubic models respectively.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2023)
Article
Astronomy & Astrophysics
Sam Young
Summary: In this study, we reassess the impact of local-type non-Gaussianity on the abundance of primordial black holes (PBHs) and find that the effect is much less significant than previously believed. The non-Gaussianity parameters need to be significantly larger to have a similar effect as before, which weakens the constraints on PBH abundance and the primordial power spectrum dependence on non-Gaussianity parameters. Furthermore, we question the existing calculations of PBH abundance due to the correlation between curvature perturbation and compaction.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Astronomy & Astrophysics
Jia-Xi Feng, Fengge Zhang, Xian Gao
Summary: In this study, we investigate the polarized properties of scalar induced gravitational waves (SIGWs) in the Chern-Simons gravity with a dynamical scalar field. We find that the correction from the parity-violating Chern-Simons term is negligible on large scales, indicating a very small degree of circular polarization for these gravitational waves.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2023)
Article
Astronomy & Astrophysics
Katsuki Aoki, Mohammad Ali Gorji, Shinji Mukohyama, Kazufumi Takahashi
Summary: The study focuses on the relativistic effective field theory describing a non-dissipative gravitating continuum, uncovering the more symmetric continuum called aether and its behavior akin to a cosmological constant. Formulating the EFT in the unitary/comoving gauge offers a geometrical understanding of continua, while a thread-based spacetime decomposition allows for systematic identification of invariant building blocks at higher orders in the derivative expansion. Additionally, the linear dynamics analysis demonstrates the acquisition of mass by gravitons and phonons in a gravitating background.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Astronomy & Astrophysics
Mio Kubota, Kin-ya Oda, Keigo Shimada, Masahide Yamaguchi
Summary: This study investigates cosmological perturbations ofscalar-tensor theories in Palatini formalism. By introducing actions and computing perturbations in different frames, it is shown that the sound speed of gravitational waves is unity for certain models. Additionally, the presence of ghosts and potential deviations in sound speed in Palatini formalism are explored, with the conclusion that ghost-free terms can still serve as dark energy and inflaton.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
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
Antonio De Felice, Andreas Doll, Francois Larrouturou, Shinji Mukohyama
Summary: This study investigates spherically symmetric vacuum solutions in the context of the recently proposed type-II minimally modified gravity theory. Despite local differences from the traditional metric, the solutions can be recovered to the standard metric by imposing suitable asymptotic conditions.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Astronomy & Astrophysics
Antonio De Felice, Shinji Mukohyama, Masroor C. Pookkillath
Summary: The study proposes a theory of minimally modified gravity called VCDM to reduce the H-0 tension puzzle, and after analyzing data, a transition in the expansion history of the universe is found at low-redshift z around 0.3. By using low redshift Pantheon data, the local Hubble expansion rate today within this theory is inferred to be 73.69, leading to a reduced tension within the VCDM theory.
Article
Astronomy & Astrophysics
Antonio De Felice, Shinji Mukohyama, Kazufumi Takahashi
Summary: The study focuses on U-DHOST theories, specifically examining the extra mode that arises in a generic coordinate system. The analysis reveals that this extra mode does not propagate, satisfying a three-dimensional elliptic differential equation on a spacelike hypersurface. The study also delves into how to handle this mysterious mode at both linear and nonlinear levels.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Astronomy & Astrophysics
Antonio De Felice, Shinji Mukohyama, Masroor C. Pookkillath
Summary: The Minimal theory of Massive Gravity (MTMG) includes two tensor modes in the gravity sector with non-zero mass, showing self-accelerating and normal branches with constraints on the graviton mass for the latter branch giving an upper bound at 95%CL as mu(0) < 8.4 x 10(-34) eV.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Astronomy & Astrophysics
Jibril Ben Achour, Antonio De Felice, Mohammad Ali Gorji, Shinji Mukohyama, Masroor C. Pookkillath
Summary: This study explores disformal transformations in modified gravity by revisiting the Petrov classification, providing formulas for capturing changes in Petrov type under disformal transformation. The application of this method to various solutions reveals that Petrov type O and Petrov type D remain unchanged, while the disformed Kerr black hole shifts from type D to general Petrov type I. These results offer a new toolkit for constructing and comparing disformal solutions in modified gravity.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Physics, Multidisciplinary
Antonio De Felice, Shinji Mukohyama, Kazufumi Takahashi
Summary: In modified gravity theories, the strong coupling problem of stealth solutions can be avoided with the use of U-DHOST theories. Additionally, the existence of a nonpropagating mode in U-DHOST theories is clarified.
PHYSICAL REVIEW LETTERS
(2022)
Article
Astronomy & Astrophysics
Joshua A. Kable, Giampaolo Benevento, Noemi Frusciante, Antonio De Felice, Shinji Tsujikawa
Summary: This study investigates the physics of late-time cosmic acceleration using the cross-correlation power spectrum of the integrated Sachs-Wolfe effect and galaxy fluctuations in the cosmic microwave background temperature anisotropy. Three dark energy models belonging to a subclass of Horndeski theories are considered: Galileon Ghost Condensate (GGC), Generalized Cubic Covariant Galileon (GCCG), and K-mouflage. The GGC and GCCG models predict negative ISW-galaxy cross-correlations, while the K-mouflage model predicts a positive correlation similar to the A-cold-dark-matter (ACDM) model. By fitting the best-fit models to the ISW-galaxy cross-correlation power spectrum extracted from photometric redshift surveys, it is found that the GGC and GCCG models have a poorer fit compared to the ACDM model, attributed to the suppressed ISW tails caused by the cubic-order scalar self-interaction.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Astronomy & Astrophysics
Antonio De Felice, Kei-ichi Maeda, Shinji Mukohyamaa, Masroor C. Pookkillatha
Summary: We study the collapse of a spherically symmetric dust cloud in the VCDM gravitational theory and find that it corresponds to a specific foliation of the Oppenheimer-Snyder solution in general relativity. The resulting collapse leads to a static configuration with a vanishing lapse function at a radius inside the apparent horizon. This implies the need for a UV completion to describe the physics inside the resulting black hole.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2023)
Article
Astronomy & Astrophysics
Antonio De Felice, Shinji Mukohyama, Kazufumi Takahashi
Summary: We investigate a generic quadratic higher-order scalar-tensor theory with a scor-datura term and show that exact stealth solutions cannot be realized in theories beyond DHOST. However, approximate stealth solutions exist, where the deviation from the exact stealth configuration is controlled by the mass scale M. The accretion of the scalar field leads to time-dependent approximately stealth solutions, which can be considered stealth at astrophysical scales for all practical purposes.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2023)
Article
Astronomy & Astrophysics
Antonio De Felice, Shinji Tsujikawa
Summary: Einsteinian cubic gravity is a higher-order gravitational theory that allows the existence of a static and spherically symmetric black hole solution with a modified Schwarzschild geometry induced by cubic curvature terms. However, this theory is plagued by ghost and Laplacian instabilities, with at least one of the dynamical perturbations behaving as a ghost mode. Additionally, one dynamical degree of freedom shows a negative sound speed squared -1/2 for high angular momentum modes.
Article
Astronomy & Astrophysics
Masato Minamitsuji, Antonio De Felice, Shinji Mukohyama, Michele Oliosi
Summary: We investigate the dynamical properties of static and spherically symmetric systems in the self-accelerating branch of the minimal theory of bigravity (MTBG). In the first part, we study the gravitational collapse of pressureless dust and find special solutions that represent gravitational collapse in MTBG. In the latter part, we study odd-parity perturbations of the Schwarzschild-de Sitter solutions and find that for higher-multipole modes, the system reduces to four physical modes with two dynamical modes and two shadowy modes.
Article
Astronomy & Astrophysics
Masato Minamitsuji, Antonio De Felice, Shinji Mukohyama, Michele Oliosi
Summary: In this study, static and spherically symmetric solutions are investigated in the minimal theory of bigravity (MTBG). It is found that a pair of Schwarzschild-de Sitter spacetimes with different cosmological constants and black hole masses is a solution in the self-accelerating branch of MTBG, but not in the normal branch. It is also shown that the Schwarzschild-de Sitter solutions can become compatible with the normal branch by using different coordinates. Furthermore, it is confirmed that the self-accelerating branch of MTBG admits static and spherically symmetric general relativity solutions with matter written in the spatially flat coordinates, including neutron stars with arbitrary matter equations of state. Finally, it is demonstrated that nontrivial solutions in the self-accelerating branch are given by the Schwarzschild-de Sitter metrics written in nonstandard coordinates.
Article
Astronomy & Astrophysics
Antonio De Felice, Shinji Mukohyama, Masroor C. Pookkillath
Summary: In this work, a class of extended minimal theories of massive gravity is introduced, which does not require the same cosmological solutions as the de Rham-Gabadadze-Tolley massive gravity. The theory is constructed to have only two degrees of freedom in the gravity sector, and the unwanted degrees of freedom are removed by adding constraints. The gravitational waves are the only propagating gravitational degrees of freedom that acquire a nontrivial mass. The theory's effective gravitational force is investigated by studying cosmological scalar perturbations. The class of models is further restricted by imposing certain conditions, leading to finite contributions of the Integrated Sachs-Wolfe (ISW) effect and the possibility for nontrivial modifications of gravity.
Article
Astronomy & Astrophysics
Antonio De Felice, Shinji Mukohyama, Masroor C. Pookkillath
Summary: Static, spherically symmetric solutions representing stars made of barotropic perfect fluid are studied in the context of two theories of type-II minimally modified gravity, VCDM and VCCDM. It is found that the solutions in V(C)CDM exactly coincide with the ones in GR.
Article
Astronomy & Astrophysics
Jose C. N. de Araujo, Antonio De Felice, Suresh Kumar, Rafael C. Nunes
Summary: The authors investigated the minimal theory of massive gravity (MTMG) with the Planck-cosmic microwave background (CMB) data for the first time and found that the MTMG model can provide solutions to tensions in observational data within the A cold dark matter cosmology. They also showed that the graviton in the MTMG scenario has a small, positive, non-zero mass and that the theory remains consistent with CMB observations, positioning it as a viable candidate among other modified gravity theories.
