Article
Physics, Particles & Fields
Pham Van Ky, Nguyen Thi Hong Van, Nguyen Anh Ky
Summary: The f(R) theory of gravitation is developed around the general theory of relativity with a cosmological constant in a flat FLWR geometry. An explicit cosmological solution is derived, showing how the Hubble parameter depends on time, cosmological constant, and matter density. This approach is applied to specific test models, including one that describes three phases of the Universe's evolution. The perturbative f(R) theory can be considered as an effective GR with the cosmological constant replaced by an effective parameter.
EUROPEAN PHYSICAL JOURNAL C
(2023)
Article
Physics, Nuclear
Ion I. Cotaescu
Summary: This paper presents the kinematics of spatially flat FLRW spacetimes in local charts using physical coordinates, and discusses the conservation of momentum, definition of peculiar momentum, and energy loss phenomena in terms of cosmic time and proper Cartesian space coordinates. Additionally, examples of de Sitter expanding universe and a new Milne-type spacetime are extensively analyzed in this framework.
Article
Astronomy & Astrophysics
Chethan Krishnan, Roya Mohayaee, Eoin O. Colgain, M. M. Sheikh-Jabbari, Lu Yin
Summary: This study explores the correlation between higher H-0 and the CMB dipole direction based on the angular distribution of type Ia supernovae in the Pantheon compilation. It suggests the possibility of probing anisotropic Hubble expansions and provides concrete predictions for future inferences of H-0.
Article
Physics, Multidisciplinary
Vaclav Vavrycuk
Summary: The commonly used FLRW metric must be modified to accurately predict cosmological redshift, and the proposed conformal FLRW metric fits observational data well.
FRONTIERS IN PHYSICS
(2022)
Article
Physics, Particles & Fields
Patrocinio Perez, Ulises Nucamendi, Roberto De Arcia
Summary: The study applies dynamical system theory tools to examine the structure of a non-gravitational interaction between pressureless dark matter and dark energy described by a scalar field phi. It derives a coupling function that is linearly dependent on dark matter density and the kinetic term of the scalar field, and analyzes various scenarios to understand cosmological evolution. A notable finding is the emergence of a separatrix for alpha not equal to 0, which significantly modifies the phase space structure, a novel feature not previously mentioned in the literature.
EUROPEAN PHYSICAL JOURNAL C
(2021)
Article
Multidisciplinary Sciences
Cosmin Andrei, Anna Ijjas, Paul J. Steinhardt
Summary: In this paper, we investigate how short the remaining period of expansion can be given current observational constraints on dark energy, and discuss how this scenario fits naturally with cyclic cosmologies and recent conjectures about quantum gravity.
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
(2022)
Article
Astronomy & Astrophysics
Marina -Aura Dariescu, Ciprian Dariescu, Vitalie Lungu, Cristian Stelea, Alexandru Ioan Cuza
Summary: In this work, the authors reconsider the solution describing black holes surrounded by a quintessencelike fluid. They show that this geometry is an exact solution of the Einstein equations coupled to nonlinear electrodynamics, and investigate the motion of charged particles in this geometry as well as the interpretation of black-hole thermodynamics.
Article
Astronomy & Astrophysics
Fulvio Melia
Summary: Spontaneous symmetry breaking in grand unified theories is believed to have generated a large number of magnetic monopoles in the early Universe. However, none of these massive particles has ever been found, possibly because inflation diluted their number. If the inflationary paradigm is invalid, it would create a cosmological 'monopole problem' and pose a challenge to the standard model of particle physics. In the Rh = ct universe, all such anomalies are eliminated naturally, and the monopole energy density would be undetectable.
PHYSICS OF THE DARK UNIVERSE
(2023)
Article
Astronomy & Astrophysics
Bijan Saha
Summary: In this study, the role of a nonlinear spinor field in the evolution of the universe within a FLRW cosmological model is investigated. The FLRW models in both Cartesian and spherical coordinates are used. It is observed that the energy-momentum tensor of the spinor field has non-diagonal components when the FLRW model is given in spherical coordinates, which is not the case for Cartesian coordinates. These non-diagonal components are independent of both the nonlinearity of the spinor field and the curvature parameter k. The presence of these components imposes constraints on the spinor field. Open, flat, and closed geometries are considered, and the spinor field is used to simulate different types of sources including dark energies. Some qualitative numerical solutions are provided.
Article
Multidisciplinary Sciences
Vaclav Vavrycuk
Summary: Recent observations show that the Universe is partially opaque due to light absorption by cosmic dust. This paper studies the evolution of the Universe with increasing cosmic opacity and incorporates radiation pressure into the Friedmann equations. The model predicts a cyclic expansion/contraction of the Universe with no Big Bang, and removes fundamental tensions of the standard cosmological model.
JOURNAL OF ADVANCED RESEARCH
(2023)
Article
Astronomy & Astrophysics
Amin Salehi, M. Pourali, Y. Abedini
Summary: This paper investigates the Hubble IR cutoff in Barrow holographic dark energy with neutrino masses using the latest observational data. It shows that the holographic dark energy disfavors the Hubble parameter as a candidate for the IR cutoff in spatially flat FRW cosmologies. The exponent parameter Delta in Barrow holographic dark energy significantly affects the EoS parameter and under certain conditions, the universe could experience accelerated expansion. Constraint on the model parameters is also obtained using current cosmological observations.
GENERAL RELATIVITY AND GRAVITATION
(2023)
Article
Physics, Mathematical
Rashid Zia, Dinesh Chandra Maurya, Anil Kumar Shukla
Summary: The paper presents the f(Q,T) gravity theory and investigates a cosmological model based on it, determining the best fit model parameters using observational data and revealing the transition from decelerating to accelerating expansion of the Universe. The calculated signature-flipping point and universe's age are also provided in the study.
INTERNATIONAL JOURNAL OF GEOMETRIC METHODS IN MODERN PHYSICS
(2021)
Article
Astronomy & Astrophysics
Lorenzo Sebastiani
Summary: We investigate the thermodynamics of the apparent horizon in (non-flat) FLRW spacetime in different theories of modified gravity and in the presence of a perfect fluid. We focus on theories that have second order differential field equations on the FLRW background. Our findings suggest that it is possible to express the entropy solely in terms of the radius of the apparent horizon, which allows for the reconstruction of the gravitational lagrangian consistent with the first law.
PHYSICS OF THE DARK UNIVERSE
(2023)
Article
Multidisciplinary Sciences
Anirudh Pradhan, Archana Dixit, Dinesh Chandra Maurya
Summary: In this article, an anisotropic viscous cosmological model with f(Q) gravity is considered. The modified f(Q) gravity is investigated by applying observational constraints on the apparent magnitude. The results show that the universe undergoes accelerated expansion at late times, with dark energy dominating and an estimated current age of about 13.6 billion years.
Article
Astronomy & Astrophysics
R. K. Mishra, Heena Dua
Summary: This study examines the dynamics of the flat FLRW model of universe with time-varying cosmological constant Lambda(t) in Brans-Dicke theory. The derived cosmological model transitions from early cosmic deceleration to present cosmic acceleration, in agreement with recent empirical observations. The behavior of cosmographic parameters and the differentiation of various dark energy models from Lambda CDM model using statefinder and Om diagnostic tools are also explored in the study.
ASTROPHYSICS AND SPACE SCIENCE
(2021)
Article
Astronomy & Astrophysics
Umesh Kumar Sharma, Vipin Chandra Dubey, A. H. Ziaie, H. Moradpour
Summary: In this research, we construct the Kaniadakis holographic dark energy (KHDE) model within a nonflat Universe and investigate cosmic evolution by analyzing the density parameter, equation-of-state parameter, and deceleration parameter of the dark energy. We find that the KHDE scenario can define the thermal history of the Universe and experience a phantom regime. The model parameters are constrained using the latest observational data, and the classical stability of the KHDE model is also addressed.
INTERNATIONAL JOURNAL OF MODERN PHYSICS D
(2022)
Article
Multidisciplinary Sciences
Gunjan Varshney, Umesh Kumar Sharma
Summary: This research explores cosmic evolution in Bianchi type-III space-time using the Granda-Oliveros scale, focusing on the Tsallis entropy from Tsallis holographic dark energy. The study constructs cosmological parameters and reveals that the Universe is expanding in an accelerating form, represented by quintessence-like nature. Additionally, the research examines the geometric form of the model and explains the consistency between quintessence scalar fields and Tsallis holographic dark energy.
IRANIAN JOURNAL OF SCIENCE AND TECHNOLOGY TRANSACTION A-SCIENCE
(2022)
Article
Physics, Mathematical
A. Remya, Pankaj, Umesh Kumar Sharma
Summary: This work explores the cosmological scenario of Barrow holographic dark energy (BHDE) in relation to the time varying deceleration parameter. By investigating the evolution of a spatially flat Friedmann-Robertson-Walker (FRW) universe filled with pressure-less dark matter and BHDE density, the study analyzes the evolutionary history of essential cosmological parameters, such as the deceleration parameter, the equation of state parameter, and the density parameter. Additionally, the study examines the different structures of the model by reconstructing the scalar field potential to describe the universe's accelerated expansion phase.
INTERNATIONAL JOURNAL OF GEOMETRIC METHODS IN MODERN PHYSICS
(2022)
Article
Physics, Mathematical
Bramha Dutta Pandey, Pankaj, Umesh Kumar Sharma
Summary: This paper examines Tsallis holographic dark energy in a flat FLRW universe, with the future event horizon as an IR cutoff. The study observes suitable behavior in the model by analyzing the evolutionary behavior of parameters related to dark energy density and the equation of state. Additionally, efforts are made to reconstruct the potential of the phantom for delta > 1 with lower redshift by examining the dynamics of the scalar field.
INTERNATIONAL JOURNAL OF GEOMETRIC METHODS IN MODERN PHYSICS
(2022)
Article
Physics, Mathematical
Abdulla Al Mamon, Ambuj Kumar Mishra, Umesh Kumar Sharma
Summary: This study examines the evolution of holographic dark energy in a fractal universe, considering its interaction with Barrow entropy and dark matter. The results show that the universe recently underwent a smooth transition from deceleration to acceleration, and the behavior of holographic dark energy exhibits rich dynamics during this evolution.
INTERNATIONAL JOURNAL OF GEOMETRIC METHODS IN MODERN PHYSICS
(2022)
Article
Astronomy & Astrophysics
Pankaj, Bramha Dutta Pandey, P. Suresh Kumar, Umesh Kumar Sharma
Summary: This paper presents a model for studying the nature of dark energy using nonextensive Tsallis entropy. The model is based on the Karolyhazy relation, which combines ideas from quantum physics and general relativity. The agegraphic dark energy (ADE) models are proposed to explain the energy density of quantum fluctuations in spacetime. The study examines the cosmological implications of the hypothesized dark energy model, considering the expansion of the universe and the flow of energy between the dark matter and dark energy sectors.
INTERNATIONAL JOURNAL OF MODERN PHYSICS D
(2022)
Article
Astronomy & Astrophysics
P. Suresh Kumar, Pankaj, Umesh Kumar Sharma
Summary: In order to maintain consistency, entropy relations and holography are applied to the entire universe within a framework of gravitational non-extensivity, using the standard definition of universe horizon entropy known as Tsallis non-extensive entropy. The Tsallis holographic dark energy model, quantified by a dimensionless parameter 6, is an attempt to test the concept of dark energy within the framework of holographic principle and entropy formalism. The behavior of Tsallis holographic dark energy is analyzed by choosing an appropriate value for the dimensionless parameter 6.
Article
Physics, Mathematical
Ajitesh Kumar, Vandna Srivastava, Vipin Chandra Dubey, Umesh Kumar Sharma
Summary: By utilizing a Barrow entropy and the standard holographic method within a cosmic framework, we propose the Barrow agegraphic dark energy (BADE) model which incorporates the Universe age as an infrared cutoff scale in a flat FLRW Universe. The trajectories of the BADE model have been plotted in the (r,s) and (r,q) planes, revealing that the model exhibits characteristics of both Chaplygin gas and quintessence for various values of delta. Additionally, we examined the BADE model without interaction in the (omega(D),omega'(D)) plane, utilizing the observational data from Planck 2018 results for VI-lambda CDM and obtaining a dynamic study with the energy density BADE parameter omega(0)(D) = 0.70 and H-0 = 67.
INTERNATIONAL JOURNAL OF GEOMETRIC METHODS IN MODERN PHYSICS
(2023)
Article
Physics, Mathematical
Pankaj, Nisha Muttathazhathu Ali, Umesh Kumar Sharma, P. Suresh Kumar, Shikha Srivastava
Summary: In this work, a new Tsallis holographic dark energy model with an apparent horizon as an infrared (IR) cutoff is constructed in a non-flat Friedmann-Lemaitre-Robertson-Walker Universe. The transition of the NTHDE Universe from a decelerating to an accelerating phase is described using the deceleration parameter and equation of state parameter with different values of the NTHDE parameter delta. The behavior of the equation of state parameter and the stability of the model are investigated using Hubble data sets and distance modulus measurements of Type Ia Supernovae.
INTERNATIONAL JOURNAL OF GEOMETRIC METHODS IN MODERN PHYSICS
(2023)
Article
Physics, Mathematical
Vipin Chandra Dubey, Mukesh Kumar, Lokesh Kumar Sharma, Umesh Kumar Sharma
Summary: In this study, the Kaniadakis holographic dark energy (KHDE) model is investigated within the framework of a flat FLRW universe using an infrared cutoff as Hubble horizon. The analysis of the deceleration, equation of state, and energy density parameters for different values of the Kaniadakis parameter kappa and C-2 is performed. The KHDE model shows a change in sign of the deceleration parameter, indicating a transition from deceleration to acceleration, which may explain the current phase shift of the Universe. The stability analysis of the KHDE model reveals its unstable behavior throughout the history of the universe. Additionally, model parameters are optimized using distance modulus measurements from the Union 2.1 dataset of supernovae.
INTERNATIONAL JOURNAL OF GEOMETRIC METHODS IN MODERN PHYSICS
(2023)
Article
Astronomy & Astrophysics
Umesh Kumar Sharma, Mukesh Kumar, Gunjan Varshney
Summary: This research investigates Barrow holographic dark energy with an energy density of ρλ=CH2-δ, considering the Hubble horizon as the IR cut-off in the f(R,T) gravity framework. The study shows that under certain limitations, Barrow holographic quintessence, k-essence, and dilation scalar field models can achieve accelerated expansion.
Article
Physics, Mathematical
A. Remya, Pankaj, Umesh Kumar Sharma
Summary: In this study, Barrow holographic dark energy (BHDE) in a flat FRW universe is analyzed using a time-dependent scale factor. The cosmic consequences are investigated by taking the Hubble horizon as the IR-cutoff. The deceleration parameter and equation of state parameter are used to demonstrate the cosmic transition and characteristics of the model. The results show agreement with recent findings and indicate that the model behaves as quintessence and eventually moves towards the Λ-CDM model. Additionally, the pressure diagram is plotted to illustrate the dominance of dark energy and the scalar field and potential explaining the universe's accelerating expansion are reconstructed.
INTERNATIONAL JOURNAL OF GEOMETRIC METHODS IN MODERN PHYSICS
(2023)
Article
Astronomy & Astrophysics
Nisha Muttathazhathu Ali, Pankaj, Umesh Kumar Sharma, P. Suresh Kumar, Ambuj Kumar Mishra
Summary: In this study, a new Tsallis holographic dark energy model is constructed in a non-flat universe, considering the effects of different parameter values on the expansion of the universe. By deriving the differential equations for the dark energy density parameter and the equation of state parameter, it is found that there are specific behaviors in both closed and open universes, and the phase transition from deceleration to acceleration can be observed through the evolution of the deceleration parameter. The study shows that the model matches well with Hubble data and exhibits stability.
MODERN PHYSICS LETTERS A
(2022)
Article
Physics, Multidisciplinary
Ambuj Kumar Mishra, Shweta, Umesh Kumar Sharma
Summary: In this paper, wormholes in 4D Einstein-Gauss-Bonnet gravity are investigated without the need for exotic matter. The results show that the negative branch wormhole solutions satisfy the null energy conditions (NEC) throughout the entire space-time, while the positive branch reduces exactly to Morris-Thorne of GR.
PRAMANA-JOURNAL OF PHYSICS
(2022)
Article
Physics, Multidisciplinary
Umesh Kumar Sharma
Summary: The research delves into the Tsallis holographic dark energy, demonstrating the evolutionary behavior of the model under different Tsallis exponents and describing the phantom scalar field in certain conditions.
PRAMANA-JOURNAL OF PHYSICS
(2022)
