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
Pediatrics
Ranjith Kumar Manokaran, Harshavardhan Mahalingam, Shubha Shankaranarayanan, Devaram Sowmya, Padmasani Venkat Ramanan
Summary: AESD is a clinicoradiological syndrome in children caused by viral or bacterial infections. This case report presents an infant with dengue infection and AESD, who recovered completely following treatment with human immunoglobulin therapy. The study expands the reported spectrum of neurological manifestations of dengue infection.
JOURNAL OF TROPICAL PEDIATRICS
(2021)
Article
Astronomy & Astrophysics
Joseph P. Johnson, Archana Sangwan, S. Shankaranarayanan
Summary: In this study, we investigate an interacting field theory model for the interaction between dark energy and dark matter. By comparing with cosmological data, we find that this interacting model is consistent with observations and obtain quantitative tools to distinguish between interacting and non-interacting dark energy scenarios.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Physics, Multidisciplinary
Manu Srivastava, S. Shankaranarayanan
Summary: This study investigates the effects of quantum fluctuations of scalar field stress-tensors in black-hole space-times using semi-classical analysis. A critical length-scale is obtained at which gravitational interactions become significant.
Review
Astronomy & Astrophysics
S. Shankaranarayanan, Joseph P. Johnson
Summary: This review discusses three aspects of modified gravity (MG) theories: why we need to consider MG theories, how to modify general relativity (GR), and the observational consequences. The review aims to serve as a reference for theorists, observers, and those interested in bridging the gap between theory and observations, by exploring the differences between GR and modified gravity theories.
GENERAL RELATIVITY AND GRAVITATION
(2022)
Article
Astronomy & Astrophysics
Ashu Kushwaha, Abhishek Naskar, Debottam Nandi, S. Shankaranarayanan
Summary: At astrophysical and cosmological scales, there is a detectable amount of magnetic field. This paper proposes an Effective Field Theory (EFT) approach to describe the origin and generation mechanism of magnetic field in the early Universe, based on expansion about the Hubble parameter and its derivatives. By analyzing a specific model, it is confirmed that broken conformal invariance and causal propagation are two necessary conditions for the generation of primordial magnetic fields.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2023)
Article
Astronomy & Astrophysics
Saurya Das, S. Shankaranarayanan, Vasil Todorinov
Summary: A recent study establishes the correspondence between the Generalized Uncertainty Principle (GUP) and Modified theories of gravity, particularly Stelle gravity. The study investigates the implications of this correspondence for inflation and cosmological observables by evaluating the power spectrum of perturbations using two different methods. By utilizing PLANCK observations, the GUP parameter gamma(0) is determined and its value is used to study the effects of quantum gravity on the power spectrum of primordial gravitational waves and their detectability in future detectors.
Article
Physics, Multidisciplinary
Indranil Das, Joseph P. Johnson, S. Shankaranarayanan
Summary: In this study, two classes of Ricci-inverse models are considered and numerically solved. The results show that these two classes of models cannot explain the late-time evolution of the Universe. By using the reduced action approach, it is found that the no-go theorem for Ricci-inverse gravity models cannot be bypassed. Finally, the implications for early-Universe cosmology are discussed.
EUROPEAN PHYSICAL JOURNAL PLUS
(2022)
Article
Astronomy & Astrophysics
Swastik Bhattacharya, S. Shankaranarayanan
Summary: This work describes the interaction between non-stationary black hole horizons and external fields using effective field theory methods, providing insights beyond classical black hole physics. The authors construct a low-energy effective field theory description for the horizon-fluid of a 4-dimensional, asymptotically flat, Einstein black hole, finding that a deformed Conformal Field Theory can naturally satisfy the requirements of near-horizon symmetries and length scales due to external perturbations. The study also determines the mass and viscosity of the horizon-fluid, which affects the scrambling time of black holes.
Article
Multidisciplinary Sciences
Avijit Chowdhury, Semin Xavier, S. Shankaranarayanan
Summary: Motivations for modified gravity have grown in the last two decades, both at theoretical and observational levels. While f(R) and Chern-Simons gravity have received more attention as simpler generalizations, they lack other modes present in modified theories of gravity. In contrast, quadratic gravity (Stelle gravity) is a more general second-order modification that includes a massive spin-2 mode. Through the study of gravitational wave energy-flux and backreaction on the spacetime of black holes, it has been demonstrated that the massive spin-2 mode carries more energy than the spin-0 mode. These effects are particularly pronounced for intermediate-mass black holes, making them important targets for LISA.
SCIENTIFIC REPORTS
(2023)
Article
Astronomy & Astrophysics
Sandra Byju, Kinjalk Lochan, S. Shankaranarayanan
Summary: We investigate generalized thermalization in an isolated free fermionic chain that undergoes a sudden quench from an out of equilibrium initial state. We focus on the evolution of local observables after the quench, such as occupation number, hopping between nearest neighbors, information sharing, and out-of-time-order correlations. We find that the system relaxes to a generalized Gibbs ensemble, despite the belief that noninteracting or free fermionic models do not relax to such an ensemble. Our analysis reveals that the internal interactions within the system become less important once the quench is sufficiently strong.
Article
Astronomy & Astrophysics
S. Mahesh Chandran, S. Shankaranarayanan
Summary: In time-independent quantum systems, the entanglement entropy possesses a scaling symmetry that the energy of the system does not have. We extend this symmetry to time-dependent systems including coupled harmonic oscillators and quantum scalar fields. These time-dependent systems exhibit a dynamical scaling symmetry that preserves the evolution of various measures of quantum correlations. It is shown that instabilities in these systems can be quantified using scrambling time and Lyapunov exponents, and that the delayed decay of the Loschmidt echo is determined by inverted modes. We also discuss the implications of zero modes and inverted modes in time-dependent massive scalar fields in different spacetimes, such as cosmological and black hole spacetimes.
Article
Education, Scientific Disciplines
Karthik Rajeev, S. Shankaranarayanan
Summary: Formulating a satisfactory quantum theory of gravity is a challenging task in theoretical physics, and Thanu Padmanabhan's pioneering works in black hole physics, quantum cosmology, and quantum gravity are considered insightful and unique. This article briefly reviews his contributions in these fields.
RESONANCE-JOURNAL OF SCIENCE EDUCATION
(2023)
Article
Astronomy & Astrophysics
Susmita Jana, S. Shankaranarayanan
Summary: The gravitational memory effect and its electromagnetic analog are potential probes in the strong gravity regime. Researchers evaluated the electromagnetic (EM) memory effect for comoving observers in arbitrary curved spacetimes, providing a transparent and easily applicable expression for the EM memory in general curved spacetimes. The master equation derived in this study allows for a physical understanding of the contribution to the EM memory and demonstrates the advantages of this approach in obtaining EM memory for specific spacetime geometries.
Article
Statistics & Probability
S. Farzana, Gayathri Harikumar, S. Shankaranarayanan, N. Vikram
Summary: Banks are no longer solely focused on satisfying consumers, but are now paying attention to providing a delightful banking experience. Research shows that e-services have an impact on customer satisfaction in the banking industry, with responsiveness and reliability being the most important factors.
JOURNAL OF STATISTICS AND MANAGEMENT SYSTEMS
(2022)
Article
Astronomy & Astrophysics
Semin Xavier, Alan Sunny, S. Shankaranarayanan
Summary: In this study, an exact time-dependent solution modeling evaporating black holes in the cosmological background was obtained, considering mass-loss, mass distribution, and cosmological background as the three aspects of primordial black holes (PBHs). The research also found that the decay rate of PBHs is positively correlated with their mass. This is significant for understanding the theoretical constraints on PBHs as dark matter.
