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
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
Damiano Anselmi
Summary: In this study, inflationary perturbation spectra and the quantity r + 8n(T) were computed to the next-to-next-to-leading log order in quantum gravity with solely virtual particles. The spectra are functions of inflationary running coupling and satisfy cosmic renormalization group flow equations. Tensor fluctuations receive contributions from the spin-2 fakeon chi(mu nu), while the scalar spectrum's dependence on chi(mu nu) starts from alpha(2) corrections. The theoretical predictions have errors ranging from alpha(4) to alpha(3), and nontrivial issues regarding the fakeon projection at higher orders are discussed.
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
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
Luca Marchetti, Daniele Oriti
Summary: This research derives effective dynamics for scalar cosmological perturbations from quantum gravity in the framework of group field theory condensate cosmology. It establishes a connection between fundamental quantum gravity models and cosmological observations.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
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
Yugo Abe, Takeo Inami, Keisuke Izumi
Summary: The study reveals that in the quadratic curvature theory of gravity, the tree-level unitarity bound is violated in the UV region, but the S-matrix unitarity is satisfied. The theory is renormalizable and the failure of tree unitarity acts as a counter example to Llewellyn Smith’s conjecture. A new conjecture is proposed suggesting that S-matrix unitarity and renormalizability share similar conditions, which is demonstrated through matter-graviton scattering in R-mu nu(2) gravity.
MODERN PHYSICS LETTERS A
(2021)
Article
Physics, Multidisciplinary
Eugeny Babichev, Keisuke Izumi, Norihiro Tanahashi, Masahide Yamaguchi
Summary: We discuss a field transformation from fields psi(a) to other fields phi(i) involving derivatives. We derive conditions for this transformation to be invertible, primarily focusing on the simplest case that maps between a pair of fields and involves up to their first derivatives. Our derivation is based on the method of characteristics, which is used to count the number of independent solutions of a given differential equation. We show some non-trivial examples of invertible field transformations with derivatives, and provide a rigorous proof that a simple extension of the disformal transformation involving a second derivative of the scalar field is not invertible.
PROGRESS OF THEORETICAL AND EXPERIMENTAL PHYSICS
(2022)
Article
Physics, Particles & Fields
Keisuke Izumi, Tetsuya Shiromizu, Kenta Suzuki, Tadashi Takayanagi, Norihiro Tanahashi
Summary: In this paper, we study various dynamical aspects of the AdS/BCFT correspondence in higher dimensions. By analyzing the metric perturbation in the gravity dual, we study the properties of the holographic stress energy tensor and calculate the stress energy tensor for a locally excited state on a half plane in a free scalar CFT. We also study the behavior of the scalar field perturbation in the AdS/BCFT setup and find complete reflections. Moreover, we provide support for the Island/BCFT correspondence in higher dimensions by comparing the entanglement entropy of a BCFT computed from the AdS/BCFT with that calculated from the Island formula. Finally, we show how one point functions in a BCFT can be calculated in our gravity dual.
JOURNAL OF HIGH ENERGY PHYSICS
(2022)
Article
Physics, Particles & Fields
Yugo Abe, Takeo Inami, Keisuke Izumi
Summary: This paper investigates the matter-graviton scattering amplitude in the gravitational theory of quadratic curvature, which includes an R-mu upsilon(2) term in the action. The existence of negative norm states leads to the violation of unitarity bound, although a version of unitarity bound for S matrix unitarity is still held due to the cancelation among positive and negative norm states in the unitarity summation in the optical theorem. The violation of unitarity bound serves as a counter example for Llewellyn Smith's conjecture, and a new conjecture relating S-matrix unitarity to renormalizability is proposed.
JOURNAL OF HIGH ENERGY PHYSICS
(2023)
Correction
Astronomy & Astrophysics
Masaya Amo, Keisuke Izumi, Yoshimune Tomikawa, Hirotaka Yoshino, Tetsuya Shiromizu
Correction
Astronomy & Astrophysics
Masaya Amo, Keisuke Izumi, Yoshimune Tomikawa, Hirotaka Yoshino, Tetsuya Shiromizu
Article
Astronomy & Astrophysics
Tetsuya Shiromizu, Keisuke Izumi, Kangjae Lee, Diego Soligon
Summary: Based on current models of the accelerating Universe, this study takes into account the variables of angular momentum, gravitational waves, and matter and finds an upper bound for the area of stable marginally outer trapped surfaces. Compared to previous studies, which consider only some of these variables, the bound is tighter and provides a concrete limit on the size of black holes, particularly relevant in the early Universe.
Article
Astronomy & Astrophysics
Kangjae Lee, Tetsuya Shiromizu, Keisuke Izumi, Hirotaka Yoshino, Yoshimune Tomikawa
Summary: This article reexamines the concept of the attractive gravity probe surface as an indicator for gravity strength, proposing three new variant concepts and providing refined inequalities for the four types of these surfaces, considering angular momentum, gravitational waves, and matter.
Article
Astronomy & Astrophysics
Takeshi Kobayashi, Daniele Perri
Summary: In this study, we present new bounds on the cosmic abundance of magnetic monopoles by examining the survival of primordial magnetic fields during the reheating and radiation-dominated epochs. These new bounds can be stronger than the conventional Parker bound and bounds from direct searches. We also investigate the monopoles produced by the primordial magnetic fields themselves and derive additional conditions for the survival of the primordial fields.
Article
Astronomy & Astrophysics
Masaya Amo, Tetsuya Shiromizu, Keisuke Izumi, Hirotaka Yoshino, Yoshimune Tomikawa
Summary: By analyzing the behavior of geometrical quantities in the Bondi coordinates, the condition for a nonexpanding photon surface to exist is determined by a key quantity that determines the fate of photons initially emitted in angular directions. In four dimensions, such a surface can exist even near future null infinity with enormous energy flux, while in higher-dimensional cases, it is not possible. This result also suggests that the dynamically transversely trapping surface can have arbitrarily large radius in four dimensions.
Article
Astronomy & Astrophysics
Kangjae Lee, Tetsuya Shiromizu, Keisuke Izumi
Summary: This paper reexamines the proposal of a loosely trapped surface as an indicator for strong gravity and an attractive gravity probe surface for gravity. Refined inequalities for them are derived by taking into account angular momentum, gravitational waves, and matters.
Article
Physics, Particles & Fields
Eugeny Babichev, Keisuke Izumi, Norihiro Tanahashi, Masahide Yamaguchi
Summary: This article explicitly formulates the necessary and sufficient conditions for the local invertibility of a field transformation involving derivative terms, by applying the method of characteristics of differential equations. The obtained results generalize the widely used inverse function theorem and will have many useful applications in modern physics and mathematics where field transformations are common.
ADVANCES IN THEORETICAL AND MATHEMATICAL PHYSICS
(2021)
Article
Astronomy & Astrophysics
Keisuke Izumi, Yoshimune Tomikawa, Tetsuya Shiromizu
Summary: In this paper, we discuss the uniqueness of asymptotically flat and static spacetimes in the n-dimensional Einstein-conformal scalar system, pointing out a potential singularity in the field equations and the corresponding uniqueness result outside a certain surface associated with the singular point.
Article
Astronomy & Astrophysics
Masaya Amo, Keisuke Izumi, Yoshimune Tomikawa, Hirotaka Yoshino, Tetsuya Shiromizu
Summary: This study investigates the behavior of null geodesics near future null infinity in asymptotically flat spacetimes. The analysis is conducted for general dimensions, highlighting the difference between four-dimensional and higher-dimensional cases. In four dimensions, additional assumptions are required for null geodesics to reach future null infinity, while in higher dimensions, such assumptions are not necessary and gravitational waves do not affect the asymptotic behavior of null geodesics.
Article
Physics, Multidisciplinary
Kouki Kushihara, Keisuke Izumi, Tetsuya Shiromizu
Summary: The study on de Sitter entropy in the braneworld model with Gauss-Bonnet/Lovelock terms reveals that the de Sitter entropy computed through the Euclidean action coincides exactly with the holographic entanglement entropy.
PROGRESS OF THEORETICAL AND EXPERIMENTAL PHYSICS
(2021)
