Article
Physics, Multidisciplinary
J. A. Astorga-Moreno, E. A. Mena-Barboza
Summary: Modified gravity theories have gained significant attention in the past decade. This study utilizes deformed phase space in f(R) gravity to derive the Wheeler-DeWitt equation in the Quantum Cosmology scenario for a Friedmann-Lemaitre-Robertson-Walker model. Furthermore, a function f(R) that corresponds to the -Cold Dark Matter model is also considered.
Article
Astronomy & Astrophysics
Chen Lan, Yi-Fan Wang
Summary: In this paper, the concept of ridgelines is introduced to investigate the semiclassical predictions of wave packets with arbitrary widths in quantum mechanics and quantum cosmology. The contour and the stream approaches are used for the exact calculation of the ridgelines. The results show that the semiclassical predictions in toy models have more abundant solutions than the classical theory, and interestingly, they may deviate from classical solutions due to quantum corrections.
Article
Physics, Multidisciplinary
Amir H. Rezaei, T. Azizi, N. Rashidi
Summary: In this paper, an exponential form of modified gravity is considered. The theory is consistent with local tests and various aspects of the model are investigated, including the static solution, scalar field potential, and stability of critical points. The realization of inflation and its graceful exit in this model are also studied.
Article
Multidisciplinary Sciences
Polina Petriakova, Arkady Popov, Sergey Rubin
Summary: Studying the evolution of the Universe from sub-Planckian scale to present times reveals the requirement for exponential expansion of space and significant restrictions on parameter values of a function f(R). The initial metric of the Universe is assumed to be maximally symmetric with positive curvature.
Article
Multidisciplinary Sciences
Joshua Foo, Estelle Asmodelle, Austin P. Lund, Timothy C. Ralph
Summary: Bohmian mechanics is a nonlocal hidden-variable interpretation of quantum theory that predicts deterministic trajectories for particles in spacetime. This study proposes an approach to construct relativistic Bohmian-type velocity field and applies it to obtain relativistic spacetime trajectories of photons in a Michelson-Sagnac interferometer.
NATURE COMMUNICATIONS
(2022)
Article
Physics, Multidisciplinary
Sijo K. Joseph
Summary: Researchers have discovered a potential breakthrough in the quest for exotic matter by coupling the Alcubierre warp drive metric with a quantum mechanical scalar matter field. By mapping the requirement of exotic matter into a conformal wave equation, the problem can be expressed as a fourth-order partial differential equation in terms of the quantum mechanical density. This research reveals that finding a proper quantum mechanical density that satisfies the proposed partial differential equation is the key to solving the exotic matter problem.
Article
Astronomy & Astrophysics
Saurya Das, Sourav Sur
Summary: Recent research has shown that any observed potential can be generated by a suitable wave function. This study focuses on the gravitational potential and determines the wave function that produces it, suggesting that the observed gravitational interaction at all length scales can be explained by an underlying wave function. The implications of this result are discussed.
INTERNATIONAL JOURNAL OF MODERN PHYSICS D
(2022)
Article
Astronomy & Astrophysics
Mariaveronica De Angelis, Laria Figurato, Giovanni Montani
Summary: In this study, the canonical quantum dynamics of the isotropic universe in metric f(R) gravity theory is analyzed, with investigations into Schrodinger evolution in both vacuum and scalar field cases. The results show nonspreading wave packet profiles in vacuum and increased localization of universe volume when an external scalar field is present. This suggests a spontaneous mechanism for Universe classicalization in metric f(R) gravity, with implications for the transition from a Planckian Universe to a classical de-Sitter phase.
Article
Physics, Particles & Fields
Isil Basaran Oz, Kazuharu Bamba
Summary: This paper investigates the f(R) theory in static cylindrically symmetric and plane-symmetric spacetimes. Solutions to the field equations of these models are found using the Noether symmetry method, leading to the discovery of new solutions. Additionally, the GR limit for each case is examined.
EUROPEAN PHYSICAL JOURNAL C
(2022)
Article
Physics, Multidisciplinary
Athanasios C. C. Tzemos, George Contopoulos
Summary: We investigate the impact of unstable points on the Bohmian flow in a 2D system composed of two non-interacting harmonic oscillators. Specifically, we analyze the unstable points in both the inertial frame of reference and the frame of reference of the moving nodal points, considering cases with 1, 2, and multiple nodal points. Furthermore, we examine the contributions of ordered and chaotic trajectories to the Born distribution, and whether the latter can be accessed by an initial particle distribution that does not conform to Born's rule.
Article
Astronomy & Astrophysics
Andronikos Paliathanasis
Summary: By studying the quantum potential of the Szekeres system, new conservation laws were discovered, leading to a wave function that can modify the system. These findings suggest that quantum correction terms add pressure to the solutions of Szekeres spacetimes.
Article
Astronomy & Astrophysics
Jafar Sadeghi, Behnam Pourhassan, Saeed Noori Gashti, Elaheh Naghd Mezerji, Antonio Pasqua
Summary: In this study, the inflationary scenario in logarithmic f (R) gravity is examined, with a focus on the constant-roll rate of inflation. The cosmic evolution of the logarithmic f (R) gravity is investigated using constant-roll conditions, and numerical and graphical analyses are presented. The resulting potential satisfying the constant-roll conditions is obtained and tested against the refined swampland conjecture and the latest observable data.
Article
History & Philosophy Of Science
Andrea Oldofredi
Summary: The author presents a new mentalistic reformulation of the measurement problem in quantum mechanics, suggesting that it is essentially a determinate-experience problem. The paper clarifies that the well-known measurement problem is a mathematical consequence of quantum theory's formalism and that its mentalistic variant does not capture the relevant causes behind this issue. The essay also discusses how Bohmian mechanics and GRW theories offer clear explanations for the localization of macroscopic objects without human intervention, distinguishing between the measurement problem and the determinate-experience problem.
Article
Astronomy & Astrophysics
Shiraz Khan, S. A. Mardan, M. A. Rehman
Summary: The main theme of this work is the development of complexity-induced generalized frameworks for static cylindrical polytropes. Two different definitions of generalized polytopes with charged anisotropic inner fluid distribution are considered. A new methodology, based on the complexity factor, is presented for generating consistent sets of differential equations. The work concludes with a graphical analysis of the developed frameworks.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Astronomy & Astrophysics
Georgios Fanaras, Alexander Vilenkin
Summary: We study the quantum cosmology of 2D Jackiw-Teitelboim gravity with Lambda > 0 and calculate the Hartle-Hawking wave function for this model in a minisuperspace framework. By establishing a correspondence between JT gravity and the Kantowski-Sachs model, we obtain the semiclassical Hartle-Hawking wave function and derive a probability distribution for the dilaton field using the methods of Picard-Lefschetz theory.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Astronomy & Astrophysics
R. Moti, A. Shojai
Article
Physics, Nuclear
R. Moti, A. Shojai
INTERNATIONAL JOURNAL OF MODERN PHYSICS A
(2020)
Article
Physics, Multidisciplinary
H. Khodabakhshi, F. Shojai
Article
Astronomy & Astrophysics
R. Saadati, F. Shojai
Summary: The study introduces new aspects of the Kiselev black hole and explores null and timelike thin shell collapse in this space-time. It demonstrates that the Kiselev black hole can be matched to a de Sitter core with a thin timelike dust shell to create a non-singular space-time. The stability of the shell's stationary solutions is discussed, and suitable parameter ranges for constructing a stable stationary black hole are identified within the Kiselev geometry.
CLASSICAL AND QUANTUM GRAVITY
(2021)
Article
Astronomy & Astrophysics
Raihaneh Moti, Ali Shojai
Summary: The paper explores the effects of improving pure affine theories of gravity using the running gravitational coupling obtained from asymptotically safe gravity. By comparing with other improvement methods, a general approach for affine improvement is presented in the framework of Schrodinger-Eddington affine theory.
PHYSICS OF THE DARK UNIVERSE
(2021)
Article
Astronomy & Astrophysics
S. M. M. Rasouli, F. Shojai
Summary: This paper explores the geodesic deviation equation within the context of the Brans-Dicke theory in D dimensions, focusing on cosmological models and exact solutions. By studying cosmological models in both general relativity and the Brans-Dicke theory, the authors provide settings for dynamical systems and investigate well-known cosmological models with modified and corrected solutions. They demonstrate the potential advantages of the modified Brans-Dicke theory in describing the universe according to observational data and theoretical viewpoints.
PHYSICS OF THE DARK UNIVERSE
(2021)
Article
Astronomy & Astrophysics
F. Shojai, A. Sadeghi, R. Hassannejad
Summary: This article examines the formation of a class of regular black holes from the gravitational collapse of massive stars and presents a mathematical model and results.
CLASSICAL AND QUANTUM GRAVITY
(2022)
Article
Astronomy & Astrophysics
Raihaneh Moti, Ali Shojai
Summary: In this paper, we demonstrate the possibility of a pure quantum gravastar solution to the quantum improved Einstein equations. This object is essentially a gravastar with the thin layer of matter replaced by quantum effects. The metric of a pure quantum gravastar is obtained and its stability is discussed.
INTERNATIONAL JOURNAL OF MODERN PHYSICS D
(2022)
Article
Astronomy & Astrophysics
Sh. Khodabakhshi, M. Farhang, A. Shojai, M. S. Esmaeilian, R. Moti
Summary: The de Sitter-Godel-de Sitter phase transition (dGd) is a possible geometrical phase transition in the very early universe, leaving observable traces on matter and radiation fields. A simulation based on dGd reveals no signs of the transition, and instead shows consistency with pure inflationary power spectrum. Future large-scale surveys could provide more precise constraints on the physics of the early universe.
GENERAL RELATIVITY AND GRAVITATION
(2022)
Article
Astronomy & Astrophysics
R. Hassannejad, A. Sadeghi, F. Shojai
Summary: In this paper, the 4-dimensional Einstein-Gauss-Bonnet (EGB) gravity is treated as general relativity with an effective stress-energy tensor. The modified Oppenheimer-Snyder-Datt model of the gravitational collapse of a star in a 4-dimensional EGB black hole is studied. The interior geometry of the star is described by the spatially flat Friedmann-Robertson-Walker metric, and the matter is uniformly distributed without any assumption about its equation of state. The time evolution of event and apparent horizons is also studied.
CLASSICAL AND QUANTUM GRAVITY
(2023)
Article
Physics, Multidisciplinary
S. Cheraghchi, F. Shojai, M. H. Abbassi
Summary: Apart from assuming the inflation started at an infinite time in the past, a more realistic initial state of quantum fluctuations is imposed at a finite initial time. The α-vacuum is an important non-trivial vacuum specified by a momentum cutoff. Therefore, different k-modes have different initial time conditions, which modify the amplitude of quantum fluctuations and the corresponding power spectra. This paper investigates the impact of the α-vacuum state on the power spectrum of scalar perturbations in f(R) gravity by considering an ultraviolet cutoff. The results show that the leading order corrections to the scalar power spectra in f(R) gravity exhibit an oscillatory behavior similar to general relativity, and are sufficiently consistent with the ΛCDM model.
Article
Astronomy & Astrophysics
R. Moti, A. Shojai
Article
Astronomy & Astrophysics
H. Khodabakhshi, A. Shirzad, F. Shojai, Robert B. Mann
Article
Astronomy & Astrophysics
R. Moti, A. Shojai
Article
Astronomy & Astrophysics
S. Cheraghchi, F. Shojai
