Article
Astronomy & Astrophysics
Vsevolod R. Ivanov, Sergei Ketov, Ekaterina O. Pozdeeva, Sergey Yu Vernov
Summary: We study extensions of the Starobinsky inflation model by demanding explicit dependence of the inflaton scalar potential and the F(R) gravity function on fields and parameters in terms of elementary functions. The models are continuously connected to the original Starobinsky model via parameter changes. We modify the Starobinsky model by adding additional terms and calculate the scalar potentials, inflationary observables, and limits on the deformation parameters. We also investigate the deformation of the scalar potential of the Starobinsky model in the Einstein frame and calculate the corresponding F(R) gravity functions.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Astronomy & Astrophysics
Salomeh Khoeini-Moghaddam
Summary: In the context of Starobinsky inflation, a non-canonic field is considered in the Einstein-frame with a scalar field called scalaron. The study investigates a model with a heavy scalaron trapped at the effective potential minimum, which is consistent with Planck results for appropriate parameters. The non-canonic field, a Dirac-Born-Infeld (DBI) field, governs inflation through an implicit dependence on Scalaron the boost factor, with differences from the standard DBI model.
PHYSICS OF THE DARK UNIVERSE
(2021)
Article
Astronomy & Astrophysics
Nephtali E. Martinez-Perez, Cupatitzio Ramirez-Romero, Victor M. Vazquez-Baez
Summary: Studied two homogeneous supersymmetric extensions for the f(R) modified gravity model of Starobinsky, with bosonic sectors consistent with cosmic inflation driven by the R2 term. In the N = 2 case, the additional scalar field remains in a low energy state during inflation.
Article
Astronomy & Astrophysics
Sergei Ketov, Ekaterina O. Pozdeevad, Sergey Yu. Vernovd
Summary: This paper investigates the influence of quantum corrections inspired by superstring theory on the Starobinsky inflation model by adding the Bel-Robinson tensor term. The derived physical bounds on the parameter reveal the constraints imposed by demanding the absence of ghosts and consistency with measurements of the cosmic microwave background radiation.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Astronomy & Astrophysics
J. Bezerra-Sobrinho, L. G. Medeiros
Summary: In the context of effective theories of gravity, this paper proposes a minimalist bottom-up approach that considers 1-loop quantum corrections. It introduces four extra terms in the Einstein-Hilbert action to ensure renormalizability and accounts for the integration of massless/light matter fields. The focus is on analyzing the impact of the nonlocal term R ln (square) R on Starobinsky inflation, where it is treated as a small correction to the R-2 term. The model is shown to behave like a local model in this context, with a canonical scalar field minimally coupled to general relativity in the approximate Einstein frame. The inflationary regime of the model is studied and its free parameters are constrained through observations of CMB anisotropies.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2023)
Article
Physics, Multidisciplinary
Ekaterina O. Pozdeeva, Sergey Yu Vernov
Summary: We propose a one-parametric extension of the Starobinsky R + R-2 model by adding the (R + m(2)beta(2))(3/2) term. The value of the tensor-to-scalar ratio r can be significantly larger than in the Starobinsky model. The considered inflationary model is in a good agreement with the current observational data.
Article
Astronomy & Astrophysics
Sergei Ketov
Summary: A novel gravitational theory, inspired by string theory, is proposed in four spacetime dimensions. This theory combines the modified (R+alpha R-2) gravity motivated by the Starobinsky inflation with the Bel-Robinson-tensor-squared correction from superstrings/M-theory compactified down to four dimensions. The origin of this theory from higher dimensions is also revealed. The proposed theory, called the Starobinsky-Bel-Robinson action, has only two free parameters, making it suitable for verifiable applications in black hole physics, cosmological inflation, and Hawking radiation.
Article
Astronomy & Astrophysics
Kim Berghaus, Tanvi Karwal
Summary: Thermal friction can solve the Hubble and the large-scale structure tensions by converting scalar field energy into dark radiation. The addition of extra radiation to the Universe can also mitigate the LSS tension. However, the CMB data is incompatible with linear density perturbations of the dark radiation when injected at redshifts close to matter-radiation equality.
Article
Physics, Multidisciplinary
Aisha Siddiqa, Syeda Z. B. Mehwish, Marcio E. S. Alves
Summary: This study investigates the propagation of cosmological axial gravitational waves in the framework of the f(R) gravity with f(R)=R+lambda R2, the Starobinsky model. It analyzes the effects of the higher-order curvature term on the evolution of axial GWs and how it depends on the model parameter lambda, providing initial conditions for axial GWs in the Starobinsky model. Further investigations are needed to understand the imprint this effect may have on the spectrum of axial GWs at the end of the Starobinsky inflation.
EUROPEAN PHYSICAL JOURNAL PLUS
(2021)
Article
Physics, Nuclear
A. Belhaj, M. Benali, Y. Hassouni, M. Oualaid, M. B. Sedra
Summary: In this paper, the brane cosmological behaviors of the Starobinsky inflationary model are studied. The associated parameters, including the perturbation ones, are computed. It is found that the spectral index and tensor-to-scalar ratio of the model are in good agreement with observational data. The thermal behaviors are also investigated by varying the five-dimensional Planck mass, and acceptable reheating temperatures are obtained.
INTERNATIONAL JOURNAL OF MODERN PHYSICS A
(2022)
Article
Astronomy & Astrophysics
Sung Mook Lee, Tanmoy Modak, Kin-ya Oda, Tomo Takahashi
Summary: This article investigates the impact of six-dimensional operators on inflation predictions in the general scalar-tensor theory and concludes that suppression is necessary to maintain successful predictions.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2023)
Article
Astronomy & Astrophysics
Daniel J. H. Chung, Sai Chaitanya Tadepalli
Summary: This article presents the strongly blue tilted axionic isocurvature spectrum in an underdamped time evolution parametric regime and discovers a resonant spectral behavior that leads to a rich isocurvature spectral shape.
Article
Astronomy & Astrophysics
Andronikos Paliathanasis
Summary: The Noether symmetry analysis is applied to study a multifield cosmological model in a spatially flat FLRW background geometry. The free parameters of the model are constrained by applying Noether's theorems to ensure the existence of conservation laws, and an analytic solution is derived for the field equations.
Article
Astronomy & Astrophysics
Daniel Frolovsky, Sergei Ketov, Sultan Saburov
Summary: In this paper, the researchers adapted the Appleby-Battye-Starobinsky model to study the double cosmological inflation and formation of primordial black holes. They found that the power spectrum of scalar curvature perturbations can be enhanced, allowing the resulting primordial black holes to survive in the present universe.
MODERN PHYSICS LETTERS A
(2022)
Article
Astronomy & Astrophysics
Andreas Mantziris, Tommi Markkanen, Arttu Rajantie
Summary: Based on current experimental data, it is predicted that the vacuum state of the Universe is metastable, leading to a non-zero rate of vacuum decay. Research shows that considering the standard model and the vacuum state during inflation, a lower bound on an unknown parameter can be obtained. This bound is stronger than in single field inflation models without Higgs-inflaton coupling.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Engineering, Multidisciplinary
Andronikos Paliathanasis, Genly Leon, P. G. L. Leach
Summary: This study applies the Painleve test to the Benney and Benney-Gjevik equations, which are used to describe waves in falling liquids. The research proves that these two nonlinear 1 + 1 evolution equations pass the singularity test for the traveling-wave solutions. Algebraic solutions based on Laurent expansions are presented.
INTERNATIONAL JOURNAL OF NONLINEAR SCIENCES AND NUMERICAL SIMULATION
(2023)
Article
Engineering, Multidisciplinary
Andronikos Paliathanasis
Summary: We apply Lie theory to determine the infinitesimal generators of point transformations that leave the 3 + 1 Kudryashov-Sinelshchikov equation invariant. We classify the one-dimensional optimal system and derive all possible independent Lie invariants. The existence of travel-wave solutions is proven using the results, and singularity analysis shows that the equation possesses the Painleve property and solutions can be written using a Laurent expansion.
INTERNATIONAL JOURNAL OF NONLINEAR SCIENCES AND NUMERICAL SIMULATION
(2023)
Article
Mathematics
Andronikos Paliathanasis
Summary: In this study, we analyze the group properties of a recently proposed 2+1 extended Boiti-Leon-Manna-Pempinelli equation using the theory of Lie symmetries. We find that the equation possesses an infinite number of Lie symmetries, leading to an infinite number of solutions. By applying Lie invariants, we obtain D'Alembert-type wave solutions and identify new periodic solutions.
QUAESTIONES MATHEMATICAE
(2023)
Article
Engineering, Multidisciplinary
Andronikos Paliathanasis
Summary: This paper presents a symmetry classification study of the hyperbolic system of partial differential equations describing a drift-flux two-phase flow in a one-dimensional pipe. The results show that the fluid equations are invariant under the elements of a three-dimensional Lie algebra for general polytropic indices, but additional Lie point symmetries occur for specific values of the polytropic indices. The one-dimensional systems are investigated in each case, with similarity transformations used to reduce the fluid equations into a system of ordinary differential equations. Exact solutions are derived and the reduced systems are studied numerically.
INTERNATIONAL JOURNAL OF NONLINEAR SCIENCES AND NUMERICAL SIMULATION
(2023)
Article
Mathematics, Applied
Andronikos Paliathanasis, Genly Leon
Summary: We investigate exact solutions and the asymptotic dynamics for the Friedmann-Lemaitre-Robertson-Walker universe with nonzero spatial curvature in the fourth-order modified teleparallel gravitational theory known as f(T,B) theory. The field equations can be described in minisuperspace and can reproduce any exact form of the scale factor. Equilibrium points are calculated and their stability is analyzed. Milne and Milne-like solutions are supported, and the existence of a de Sitter universe is shown. Poincare variables are used to investigate the dynamics at infinity in order to complete the analysis.
MATHEMATICAL METHODS IN THE APPLIED SCIENCES
(2023)
Article
Multidisciplinary Sciences
Andronikos Paliathanasis
Summary: We conducted a detailed study on the potential classification of the Klein-Gordon equation in anisotropic Riemannian manifolds. Specifically, we focused on the Klein-Gordon equations in four-dimensional anisotropic and homogeneous spacetimes of Bianchi I, Bianchi III, and Bianchi V. By deriving closed-form expressions for the potential function, we were able to find the Lie and Noether symmetries of the equations. Applying previous results connecting the Lie symmetries with the collineations of the Riemannian space, we systematically solved the classification problem.
Article
Mathematics
Genly Leon, Alfredo D. Millano, Andronikos Paliathanasis
Summary: In this study, we investigate the phase space of a scalar field theory obtained through minisuperspace deformation. We consider quintessence or phantom scalar fields in the action derived from minisuperspace deformation on the Einstein-Hilbert action. Our analysis utilizes a modified Poisson algebra with alpha-deformed Poisson brackets that are linked to the Moyal-Weyl star product. We discuss both early- and late-time attractors and reconstruct the cosmological evolution. Additionally, we demonstrate that the model can exhibit the lambda CDM model as a future attractor if we start with a massless scalar field without a cosmological constant term.
Article
Mathematics
Andronikos Paliathanasis, Peter G. L. Leach
Summary: We extend our analysis on the Lie symmetries in fluid dynamics to macroscopic traffic estimation models. Specifically, we study the Aw-Rascle-Zhang model, which consists of two hyperbolic first-order partial differential equations. We determine the Lie symmetries, the one-dimensional optimal system, and the corresponding Lie invariants. We find that the admitted Lie symmetries form the four-dimensional Lie algebra A(4,12). The resulting one-dimensional optimal system is composed of seven one-dimensional Lie algebras. We use the Lie symmetries to define similarity transformations and derive new analytic solutions for the traffic model, discussing the qualitative behavior of the solutions.
Article
Physics, Multidisciplinary
Andronikos Paliathanasis
Summary: A detailed analysis is presented on the phase-space for the field equations in scalar field cosmology with a chameleon cosmology. Four different sets of potential and coupling function are considered. The H-normalization approach and dimensionless variables are used to analyze the field equations. The asymptotic solutions describe the main eras of cosmological history and the existence of acceleration solutions. The Chameleon dark energy model is concluded to be a unified model for the dark sector of the universe.
FORTSCHRITTE DER PHYSIK-PROGRESS OF PHYSICS
(2023)
Article
Mathematics
Alfredo D. Millano, Genly Leon, Andronikos Paliathanasis
Summary: We perform a detailed study of the phase-space of the field equations of an Einstein-Gauss-Bonnet scalar field cosmology for a spatially flat Friedmann-Lemaitre-Robertson-Walker spacetime. We consider the exponential function for the scalar field potential and assume two cases for the coupling function of the scalar field with the Gauss-Bonnet term: the exponential function and the power-law function. By writing the field equations in dimensionless variables and studying the equilibrium points using normalized and compactified variables, we recover previous results and discover new asymptotic solutions. These couplings provide a rich cosmological phenomenology.
Article
Mathematics, Interdisciplinary Applications
Bayron Micolta-Riascos, Alfredo D. Millano, Genly Leon, Cristian Erices, Andronikos Paliathanasis
Summary: Recently, researchers have been using fractional calculus to address cosmological problems by altering the gravitational action integral, comparing the resulting theory with observational data. By studying the phase spaces for different fractional order derivatives and matter contents, equilibrium points can be classified, providing a range for investigating cosmological history and obtaining an accelerating power-law solution for the scale factor. This paper discusses the physical interpretation of these cosmological solutions and emphasizes the influence of fractional derivatives in a theory of gravity with a scalar field.
FRACTAL AND FRACTIONAL
(2023)
Editorial Material
Physics, Nuclear
Andronikos Paliathanasis
Summary: This paper reviews the Noether symmetry analysis for Chameleon cosmology presented in R. Bhaumik, S. Dutta and S. Chakraborty, Int. J. Mod. Phys. A 37, 2250018 (2022). It shows that the classification problem for the field equations in Chameleon cosmology is still open.
INTERNATIONAL JOURNAL OF MODERN PHYSICS A
(2023)
Article
Astronomy & Astrophysics
Andronikos Paliathanasis
Summary: This study analyzes the phase-space of an alternate scalar field cosmology that combines the concepts of dark energy and the dark sector. The findings indicate that a de Sitter universe can only be achieved when the potential function is constant. The presence of a de Sitter universe depends on the functional form of the potential function, with a finite regime for a constant potential and an infinite regime for an exponential potential. The cosmological viability of the theory is discussed.
Article
Multidisciplinary Sciences
Andronikos Paliathanasis
Summary: A detailed symmetry analysis is conducted for a microscopic model of traffic flow in two-lane motorways. The model is an extension of the Aw-Rascle theory and describes flow parameters using first-order partial differential equations. The model is expressed in terms of Euler and Lagrange variables, and different Lie algebras and optimal systems are found for each variable set. The Lie symmetries are then used to derive new closed-form solutions.
Article
Astronomy & Astrophysics
Andronikos Paliathanasis, P. G. L. Leach
Summary: We provide a complete algebraic classification of the Lie symmetries for generalized Zoomeron equations. For the generalized 1 + 1 and 2 + 1 Zoomeron equations, we solve the Lie symmetry conditions to constrain the free functions. It is found that the considered differential equations have the same number of Lie symmetries as the non-generalized equations. The admitted Lie symmetries form different Lie algebras for the two cases. A one-dimensional optimal system is constructed and similarity solutions are derived, leading to kink solutions.
MODERN PHYSICS LETTERS A
(2023)
