Article
Astronomy & Astrophysics
Mindaugas Karciauskas, Jose Jaime Terente Diaz
Summary: This paper formulates slow-roll conditions in the Jordan frame and derives simple equations by comparing background quantities and approximations in different frames. These equations can be used to compute inflation model observables using Jordan frame quantities only.
Article
Physics, Particles & Fields
G. Lambiase, G. G. Luciano, A. Sheykhi
Summary: In this study, a new cosmological scenario is proposed based on Kaniadakis entropy and modified Friedmann equations. The research finds that the Kaniadakis parameter is constrained by observational limits and the correction term has a non-trivial effect on the growth of perturbations in the early stages of the Universe.
EUROPEAN PHYSICAL JOURNAL C
(2023)
Article
Astronomy & Astrophysics
Shu-Lin Cheng, Da-Shin Lee, Kin-Wang Ng
Summary: We develop a nonperturbative method to examine the quantum fluctuation effects on the single-field inflationary models in a spatially flat FRW cosmological space-time using the Hartree factorization. We derive the modified Mukhanov-Sasaki equations for the mode functions of the quantum scalar field by introducing the nonzero Delta(B) term. We find that the presence of ultra slow roll inflation triggers the growth of Delta(B) and boosts the curvature perturbations, but the cosmic friction term may inhibit this boost effect.
Article
Astronomy & Astrophysics
Nahid Ahmadi, Mahdiyar Noorbala, Niloufar Feyzabadi, Fatemeh Eghbalpoor, Zahra Ahmadi
Summary: This study investigates the impact of short non-slow-roll periods that occur during transitions between different inflationary slow-roll scenarios. By modeling a sharp transition using the Starobinsky potential, the researchers observe how stochastic noise induced by the transition affects the coarse-grained fields, resulting in a delayed boundary crossing.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Astronomy & Astrophysics
Hassan Firouzjahi, Alireza Talebian
Summary: We considered a model of single field inflation containing an intermediate phase of ultra slow-roll and calculated the induced gravitational waves from the enhanced curvature perturbations during this period. The model can accommodate the current observations but has non-trivial predictions for higher frequency ranges that can be tested in future observations.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2023)
Article
Astronomy & Astrophysics
Oliver Janssen
Summary: The study provides a detailed description of the complex O(4)-symmetric solutions to Einstein's equations on a four-ball in minimally coupled scalar field theories with a slow-roll type potential. The derivation demonstrates an anticipated result, sharpens previous findings in the classical realm of minisuperspace, and uses a complexified slow-roll approximation technique. The technique is applicable to both Hartle-Hawking and Vilenkin wave functions, which predict a family of inflationary universes with different exponential weighting in the semiclassical approximation.
CLASSICAL AND QUANTUM GRAVITY
(2021)
Article
Astronomy & Astrophysics
Pierre Auclair, Christophe Ringeval
Summary: The next generation of cosmological observations will be able to detect small deviations from a pure power law in the primordial power spectrum of curvature perturbations. These deviations correspond to the running of the spectral index and their measurement would provide as much information as the discovery of deviations from scale invariance. However, accurate parameter inference requires marginalizing over any possible higher-order uncertainties that have not been fully determined.
Article
Astronomy & Astrophysics
Keisuke Inomata
Summary: This study focuses on scalar perturbations induced by non-linear interactions at second order in perturbations. Analytic solutions for induced scalar perturbations in a perfect fluid are derived, with specific consideration for perturbations in radiation-dominated and matter-dominated eras. The evolution of induced scalar perturbations from outside to inside the horizon is also discussed using the analytic solutions.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Physics, Particles & Fields
Maksym Brilenkov, Ezgi Canay, Maxim Eingorn
Summary: Within the extension of the Lambda CDM model, this paper develops an analytical cosmological perturbation theory that allows for the presence of neutrinos or warm dark matter. The theory covers all spatial scales where the weak gravitational field regime is a valid approximation, including the case of relativistic discrete particles as sources.
EUROPEAN PHYSICAL JOURNAL C
(2023)
Article
Astronomy & Astrophysics
Gianmassimo Tasinato
Summary: The study found that introducing brief periods of nonattractor evolution in cosmological inflation can generate primordial black holes and enhance the spectrum of gravitational waves. For a single epoch of slow-roll violation, the steepest slope of the spectrum has a spectral index n(s) - 1 = 4, while multiple phases of violation result in an enhanced slope.
Article
Astronomy & Astrophysics
Alessandro Casalino, Lorenzo Sebastiani
Summary: This paper investigates the perturbation theory of Regularized Lovelock Gravity on curved FLRW spacetime, deriving a general expression for the velocity of gravitational waves. Application of the theory to slow-roll inflation on flat FLRW background yields power spectra of scalar and tensor perturbations, and equations for inflation observable quantities.
PHYSICS OF THE DARK UNIVERSE
(2021)
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
Dhiraj Kumar Hazra, Daniela Paoletti, Ivan Debono, Arman Shafieloo, George F. Smoot, Alexei A. Starobinsky
Summary: In this study, constraints on inflationary dynamics and features in the primordial power spectrum of scalar perturbations are presented using Cosmic Microwave Background temperature and polarization data from Planck 2018 data release. Models with suppression and oscillatory features are analyzed and compared with baseline slow-roll potentials. The significance of sharp features has decreased compared to previous data analysis, and bispectra are computed for the best fit candidates obtained from the analysis.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Astronomy & Astrophysics
Matteo Forconi, William Giare, Eleonora Di Valentino, Alessandro Melchiorri
Summary: Based on the latest cosmological observations, new constraints on slow roll inflation in different extended scenarios beyond the ΛCDM cosmological model have been provided. Differences in datasets can remarkably change the compatibility among different inflationary models.
Article
Astronomy & Astrophysics
Marius Oltean, Hossein Bazrafshan Moghaddam, Richard J. Epp
Summary: The quasi-local definitions of stress-energy-momentum in terms of boundary densities have proven useful in formulating and applying conservation laws in general relativity. This paper focuses on applying these definitions to cosmology, particularly using the Brown-York quasi-local stress-energy-momentum tensor. Emphasis is placed on the importance of vacuum energy in unperturbed FLRW spacetimes and the relation to effective local treatment of energy in cosmology for perturbed FLRW spacetimes.
CLASSICAL AND QUANTUM GRAVITY
(2021)
Article
Physics, Mathematical
Rabia Saleem, M. Zubair, Faisal Kramat, M. Israr Aslam, Sobia Sadiq
Summary: In this paper, we present exact anisotropic, interior solutions to the Einstein field equations with spherically symmetric geometry in the context of f(T, T) gravity. The developed model is analyzed extensively, including density profile, pressure profile, anisotropy factor, mass function, gravitational/surface redshift, compactness factor, energy bounds, stability criteria, and equilibrium condition. The analysis shows that the solutions behave well and are physically viable.
INTERNATIONAL JOURNAL OF GEOMETRIC METHODS IN MODERN PHYSICS
(2022)
Article
Astronomy & Astrophysics
R. Saleem, Aqsa Saleem, Zirwa Sohail
Summary: The paper uncovers a connection between cosmological models and the radially symmetric nonlinear Schrodinger equation, utilizing the Milne-Ermakov-Pinney equation. By applying Rastall's theory of gravity, the standard FRW cosmology is transformed into a time-independent NLS type formulation, deriving cosmological quantities in terms of Schrodinger quantities. The results suggest that Rastall's theory is a viable candidate for discussing the NLS type FRW formulation, as it is consistent with the standard theory of gravity.
INTERNATIONAL JOURNAL OF MODERN PHYSICS D
(2022)
Article
Physics, Multidisciplinary
R. Saleem, Aqsa Saleem
Summary: This article analyzes the baryogenesis of the universe in the framework of f (R, T, X) gravity under an isotropic universe model, exploring baryon asymmetry factor (BAF) in some recently proposed models of this gravity and concludes that this gravity is reliable for baryogenesis in some subspaces of the model parameter space.
EUROPEAN PHYSICAL JOURNAL PLUS
(2022)
Article
Physics, Multidisciplinary
R. Saleem, Aqsa Saleem
Summary: The aim of this article is to investigate baryogenesis in the isotropic universe model under f (R, T, Q, T) gravity, with R, T, Q, and T representing the Ricci scalar, the energy-momentum tensor (EMT) trace, non-metricity scalar, and torsion scalar, respectively. Two fluid types, w = 0 and w = 1, are used to study baryogenesis and its generalized form, using power-law and de-sitter type solutions for the scale factor. The study compares different gravity models and concludes that the linear model is more efficient in providing physically acceptable results for baryogenesis.
CHINESE JOURNAL OF PHYSICS
(2023)
Article
Physics, Multidisciplinary
Rabia Saleem, Shan Ali, M. Israr Aslam
Summary: This paper investigates the cosmological implications of Rastall gravity by using the new Tsallis agegraphic dark energy (NTADE) and Sharma-Mittal holographic dark energy (SMHDE) models. The results show that the equation of state parameter for NTADE lies in the phantom region, while for SMHDE it exhibits quintom and quintessence regions dependent on the model parameter delta. The deceleration parameter shows a phase transition from decelerating to accelerating phases for both models. The omega(D) - omega(D)' pair exhibits freezing and thawing regions for NTADE, and freezing region for SMHDE. The (J, s) pair for SMHDE indicates different dark energy eras, including phantom, quintessence, and Chaplygin gas, while the NTADE model only shows Chaplygin gas behavior. It is concluded that SMHDE is a more efficient model as it approaches the Lambda CDM limit and produces results within a stable region according to graphical analysis of the square speed of sound.
CHINESE JOURNAL OF PHYSICS
(2023)
Article
Astronomy & Astrophysics
Qanitah Ama-Tul-Mughani, Rabia Saleem, Wardat Us Salam, Sobia Sadiq
Summary: This paper presents a thermodynamic study of a Kerr-anti-de Sitter (KAdS) black hole surrounded by quintessence matter and a cloud of strings. The effects of the cloud parameter on various thermodynamic variables are analyzed, including Hawking temperature, entropy, Helmholtz free energy, Gibbs free energy, and specific heat capacity. The critical expressions of these variables are calculated using the Van-der-Waals-type equation of state and the Maxwell equal-area law. The influence of thermal fluctuations on the stability of the KAdS black hole is also discussed.
ASTROPARTICLE PHYSICS
(2023)
Article
Physics, Multidisciplinary
Rabia Saleem, M. Israr Aslam
Summary: In this paper, we investigate the existence of traversable wormholes in the framework of f(R,T) gravity with non-exotic matter and the hypothetical condition of stability inside the wormhole throat. By choosing suitable shape functions and considering the bounds on model parameters, we find the necessary conditions for stable solutions.
CHINESE JOURNAL OF PHYSICS
(2023)
Article
Physics, Multidisciplinary
Rabia Saleem, M. Israr Aslam, Komal Rasool
Summary: In this paper, we investigate the existence of traversable wormholes inspired by non-commutative geometry and conformal symmetries in Rastall-like-teleparallel gravity. Analytical solutions of the corresponding field equations are obtained using Gaussian and Lorentzian energy distributions. The viability of energy conditions at the wormhole throat is checked and the results are interpreted graphically for different choices of model parameters and Rastall parameter lambda. Constraints for the positivity of active gravitational mass are explained and the stability of the derived wormhole solutions is examined. Furthermore, embedding diagrams for the shape functions are plotted. Finally, it is concluded that the constructed wormhole solutions (sensitive to the parameter lambda) are physically viable and stable in the presence of standard matter for Gaussian energy distribution and exotic matter for Lorentzian energy distribution.
CHINESE JOURNAL OF PHYSICS
(2023)
Article
Physics, Multidisciplinary
R. Saleem, Aqsa Saleem
Summary: Entropy is a measure of disorder or randomness in a system and is unable to convert thermal energy into mechanical work. Different types of entropies, including Barrow entropy (BE), Sharma-Mittal entropy (SME), and generalized entropies are used to discuss baryogenesis. Constraints on entropy parameters are found to obtain desired physical results. Modified Friedmann field equations (FFEs) are derived using entropies and the first law of thermodynamics, resulting in modifications to the mass density and pressure content of the Universe. Baryon asymmetry factor (BAF) is shown to be non-zero even in the radiation-dominant era.
Article
Physics, Multidisciplinary
Rabia Saleem, Iqra Shahid
Summary: This manuscript explores the role of the complex quintessence field (CQF) in warm inflation within the Rastall theory of gravity. The authors investigate different models and find analytical solutions for the scalar field and effective potential required for inflation. The results demonstrate that CQF-inspired inflation in RTG provides interesting and feasible results that satisfy the Planck constraints.
Article
Physics, Mathematical
Rabia Saleem, M. Zubair, M. Israr Aslam, Faisal Karamat
Summary: The aim of this paper is to develop isotropic and anisotropic quark star configurations in the context of f(T, T) gravity in the static spherically symmetric background. The interior solutions of the field equations corresponding to a specific model are calculated, and the feasibility of the obtained solutions is confirmed by implementing several physical tests.
INTERNATIONAL JOURNAL OF GEOMETRIC METHODS IN MODERN PHYSICS
(2023)
Article
Physics, Multidisciplinary
Rabia Saleem, M. Israr Aslam, Kazuharu Bamba
Summary: In this manuscript, we obtained exact solutions for asymptotically flat wormhole geometry using symmetric f(Q) gravity. We explored two different types of f(Q) gravity models (logarithmic and exponential) along with specific choices for shape function and red-shift function. The viability of the shape function and energy conditions of the wormhole solutions were examined for each model, and the allowed parameter spaces were determined. The results showed that these modified gravity models can provide more realistic and stable wormhole geometries.
Article
Physics, Particles & Fields
Rabia Saleem, M. Israr Aslam
Summary: We study the shadow and observable features of a non-commutative charged Kiselev black hole surrounded by various profiles of accretions. The black hole's profile contains a dark interior region and a bright photon ring. The specific intensity observed from the black hole profile is darker for infalling accretion compared to the static case due to the Doppler effect.
EUROPEAN PHYSICAL JOURNAL C
(2023)
Article
Physics, Particles & Fields
Xiao-Xiong Zeng, M. Israr Aslam, Rabia Saleem
Summary: Thanks to the EHT, we now have images of supermassive black holes at the heart of the M87 galaxy. Scientists have studied the features of the black hole shadow under different gravitational backgrounds and found that the observed luminosity is mainly determined by direct emission, while the lensing ring and photon ring have smaller and negligible contributions, respectively. The observed regions and specific intensities of the emissions are also affected by changes in the model parameters. For optically thin accreting matters, the profile and specific intensity of the shadows differ between static and infalling accretion models. The findings indicate that changes in the BH state parameters affect the spacetime geometry and dynamics of the BH shadow.
EUROPEAN PHYSICAL JOURNAL C
(2023)
Article
Physics, Particles & Fields
Iqra Shahid, Rabia Saleem, Hafiza Rizwana Kausar
Summary: The study investigates the warm inflationary model in hybrid metric-Palatini f (X) gravity (HMPG) using standard and irreversible thermodynamical approach. The field equations for HMPG are derived and the cosmic inflation in f (X) gravity is explored by examining cosmic parameters such as slow-roll parameters, spectral index, running of spectral index, and tensor-to-scalar ratio. The early universe is considered as an open system and the thermodynamics and dynamical equations in f (X) gravity are applied to the interacting cosmic fluid within the basic formalism of warm inflationary model. The numerical results of thermodynamical equations are obtained and compared with the Planck-2018 data.
EUROPEAN PHYSICAL JOURNAL C
(2023)
