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
Yonadav Barry Ginat
Summary: This paper discusses the consideration of small-scale inhomogeneities in modeling the universe on a cosmic scale, introducing a multiple-scales method based on singular perturbation theory and deriving an effective Einstein equation. Conditions are established to ensure that deviations from the large-scale space-time metric do not grow unboundedly, and it is shown that these conditions are satisfied in the case of non-relativistic matter.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
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
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
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
Fengge Zhang, Jia-Xi Feng, Xian Gao
Summary: This study investigates scalar induced gravitational waves (SIGWs) in Chern-Simons modified gravity during the radiation dominated era, finding that they are circularly polarized. The study derives semi-analytic expressions to evaluate the fractional energy density of SIGWs, QGW, and reveals that the contribution from the parity-violating term is of the same order as that from general relativity.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Astronomy & Astrophysics
Katsuki Aoki, Mohammad Ali Gorji, Shuntaro Mizuno, Shinji Mukohyama
Summary: The study focuses on slow-roll single field inflation in the context of consistent D -> 4 Einstein-Gauss-Bonnet gravity. Apart from the standard attractor regime, a new attractor regime known as the Gauss-Bonnet attractor is identified, providing insights into power spectra, spectral tilts, and consistency relations. The Gauss-Bonnet term introduces a nonlinear contribution to the gravitational waves dispersion relation, offering a new scenario for primordial gravitational waves that can be tested through observations. Furthermore, the analysis delves into the non-Gaussianity of gravitational waves and estimates nonlinear parameters for different helicities.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Astronomy & Astrophysics
Alexander Ganz, Paul Martens, Shinji Mukohyama, Ryo Namba
Summary: We present an asymmetric bouncing scenario within the VCDM model, a modified gravity theory with two local physical degrees of freedom. This scenario avoids ghost and gradient instability, ad-hoc matching conditions, and anisotropic stress issues. It also successfully reproduces cosmological perturbations compatible with observations. The choice of equation of state and VCDM potential allows for an almost scale-invariant power spectrum, while satisfying the CMB bounds on the tensor-to-scalar ratio results in a blue tensor spectrum.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2023)
Article
Multidisciplinary Sciences
Julio C. Fabris, Marcelo H. H. Alvarenga, Hermano Velten
Summary: Unimodular gravity is an alternative theory to general relativity based on the Einstein-Hilbert Lagrangian with an additional constraint on the determinant of the metric. It has been shown that this theory can be recast as general relativity in the presence of a cosmological constant. However, our analysis of classical scalar perturbations around a cosmological background reveals that the usual conservation laws do not hold in this theory. We also find that perturbations in unimodular gravity exhibit instabilities, indicating that the equivalence between the two theories is not fully validated at a cosmological perturbative level.
Article
Astronomy & Astrophysics
Damiano Anselmi
Summary: This study investigates primordial cosmology with two scalar fields participating in inflation, revealing the existence of an asymptotically de Sitter cosmic RG flow in two couplings. The importance of quantum gravity theory's predictiveness and the role of RG invariance are highlighted.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Physics, Particles & Fields
Jaume Haro, Jaume Amoros, Supriya Pan
EUROPEAN PHYSICAL JOURNAL C
(2019)
Article
Astronomy & Astrophysics
Jaume de Haro, Supriya Pan, Llibert Areste Salo
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2019)
Article
Physics, Particles & Fields
Jaume Haro, Jaume Amoros, Supriya Pan
EUROPEAN PHYSICAL JOURNAL C
(2020)
Letter
Physics, Particles & Fields
Jaume Haro
EUROPEAN PHYSICAL JOURNAL C
(2020)
Article
Astronomy & Astrophysics
Jaume Haro Cases, Llibert Areste Salo
Article
Astronomy & Astrophysics
Jaume Haro, Llibert Areste Salo
GENERAL RELATIVITY AND GRAVITATION
(2020)
Article
Physics, Particles & Fields
Llibert Areste Salo, Jaume Haro
Summary: For exponential type potentials used to depict quintessential inflation, solutions with large n values do not belong to the basin of attraction of the scaling solution. A late time mechanism to exit this behavior and depict correctly the current cosmic acceleration is not needed, but an improvement introducing another parameter is required to deal with the late time acceleration of our universe.
EUROPEAN PHYSICAL JOURNAL C
(2021)
Article
Astronomy & Astrophysics
L. Areste Salo, D. Benisty, E. Guendelman, J. D. Haro
Summary: A new type of quintessential inflation based on the Lorentzian distribution has been introduced, with a simple potential that aligns with recent observations and depicts the acceleration of the universe, including reheating constraints.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Astronomy & Astrophysics
Jaume de Haro, Llibert Areste Salo
Summary: The study details important inflation models that can explain the accelerated expansion of the universe and reheating process, ultimately aligning with the theory of the Hot Big Bang universe.
Article
Astronomy & Astrophysics
Llibert Areste Salo, Jaume de Haro
Summary: This study numerically calculates the reheating temperature caused by the gravitational production of conformally-coupled superheavy particles during the phase transition from the end of inflation to the beginning of kination in two different quintessential inflation scenarios. It shows that the reheating temperature in both scenarios is higher than expected, contrary to traditional beliefs.
Article
Astronomy & Astrophysics
L. Areste Salo, D. Benisty, E. Guendelman, J. d Haro
Summary: An exponential kind of quintessential inflation potential motivated by supergravity is studied, which belongs to the class of alpha-attractor models. The model accurately depicts the early- and late-time acceleration of the Universe and is compatible with recent observations, showing an effective equation of state equal to -1 for late time cosmic acceleration.
Article
Astronomy & Astrophysics
Weiqiang Yang, Supriya Pan, Llibert Areste Salo, Jaume de Haro
Summary: The study focuses on the energy flow interaction between dark matter and dark energy, using various interaction functions in four distinct cosmic scenarios. The analysis reveals the importance of handling these interaction models with caution.
Article
Astronomy & Astrophysics
Supriya Pan, Jaume de Haro, Weiqiang Yang, Jaume Amoros
Article
Astronomy & Astrophysics
Jaume Haro, Llibert Areste Salo
Article
Astronomy & Astrophysics
Jaume Haro