Article
Astronomy & Astrophysics
Johannes Noller, Luca Santoni, Enrico Trincherini, Leonardo G. Trombetta
Summary: Scalar-tensor theories often rely on a screening mechanism to avoid large couplings with ordinary matter, in order to comply with fifth force constraints. Some subsets of Horndeski theories are found to not require such a mechanism, while others are restricted by additional bounds from gravitational waves, solar system tests, and cosmological observables. Finally, certain subsets of scalar-tensor theories are identified to precisely recover predictions of standard (linearised) Lambda CDM cosmologies in the quasi-static limit.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Astronomy & Astrophysics
Natalia Sanchez-Kuntz, Alvaro Parra-Lopez, Mireia Tolosa-Simeon, Tobias Haas, Stefan Floerchinger
Summary: Motivated by the possibility to use Bose-Einstein condensates as quantum simulators for spacetime curvature, this study investigates the effects of a time-dependent background geometry on particle production in a massless relativistic scalar quantum field. New analytical results for several expansion scenarios are derived through the analysis of fluctuations and field correlation functions.
Article
Astronomy & Astrophysics
Dina Traykova, Emilio Bellini, Pedro G. Ferreira, Carlos Garcia-Garcia, Johannes Noller, Miguel Zumalacarregui
Summary: Efforts to constrain theories of late time accelerated expansion have shown that a more careful analysis of their dynamical evolution can lead to narrower prior settings, improving precision constraints. By studying shift-symmetric scalar-tensor theories, a simplified and accurate parameterization method has been proposed, suitable for observing cosmic evolution.
Article
Astronomy & Astrophysics
A. Borowiec, A. Kozak
Summary: This paper revisits the general minisuperspace formalism for scalar tensor Friedmann-Lemake-RobertsonWalker cosmological models in an arbitrary frame. It discusses the imposition of Cauchy data on the corresponding dynamical system and extends the study to an arbitrary frame with nonminimal coupling between matter and gravity. The paper explores the gauge freedom associated with the choice of lapse function and shows the relation between particular isothermal minisuperspace coordinates and equivalent classes in the Einstein frame.
Article
Astronomy & Astrophysics
Amit Dutta Banik, Rishav Roshan, Arunansu Sil
Summary: In this proposed dark matter setup, a two component system consisting of a singlet and a hyperchargeless triplet scalars is introduced, with the ability for interconversion allowing for lower mass dark matter candidates. The model also ensures the absolute stability of the electroweak vacuum up to the Planck scale, thanks to the coupling with the scalar dark matter components.
Article
Astronomy & Astrophysics
Fotios K. Anagnostopoulos, Alfio Bonanno, Ayan Mitra, Vasilios Zarikas
Summary: This article presents a model that can explain the observed cosmic acceleration without the need for extra energy scales, exotic fields, or fine-tuning. The model extends the concept of an evolving cosmological constant and considers the scaling of the Newton constant according to the IR-fixed point hypothesis. Two different scaling relations are analyzed and shown to be in good agreement with the standard ??CDM cosmology, with one of them having no fine-tuning problem.
Article
Astronomy & Astrophysics
Genly Leon, Esteban Gonzalez, Alfredo D. Millano, Felipe Orlando Franz Silva
Summary: This paper investigates scalar field cosmologies with a generalized harmonic potential in flat and negatively curved metrics. The interaction between the scalar field and matter is taken into account. Asymptotic methods and averaging theory are used to obtain information about the solution space, and numerical simulations are used to provide evidence for the results.
CLASSICAL AND QUANTUM GRAVITY
(2022)
Article
Astronomy & Astrophysics
Genly Leon, Felipe Orlando Franz Silva
Summary: In this study, local and global phase-space descriptions and averaging methods were used to investigate the qualitative features of solutions for FLRW and Bianchi I metrics in the context of scalar field cosmologies with arbitrary potentials and couplings to matter. Equilibrium points representing various cosmological solutions such as scaling solutions, kinetic-dominated solutions, and vacuum de Sitter solutions associated with the minimum of the potential were obtained, revealing a rich cosmological phenomenology.
CLASSICAL AND QUANTUM GRAVITY
(2021)
Article
Physics, Multidisciplinary
Felipe A. Asenjo, Sergio A. Hojman
Summary: It has been shown that any cosmological anisotropic model can generate supersymmetric theories for both massless scalar and electromagnetic fields. These theories are the time-domain equivalents of supersymmetric quantum mechanics algebra theory. The variations of the anisotropic scale factors in the Universe are responsible for triggering the supersymmetry. For scalar fields, the superpartner fields evolve in two different cosmological scenarios, while for propagating electromagnetic fields, supersymmetry manifests through polarization degrees of freedom in a single Universe.
Article
Astronomy & Astrophysics
Cecilia Nagy, Zoltan Keresztes, Laszlo A. Gergely
Summary: The study explores black hole solutions of Horndeski scalar-tensor theory using a nonorthogonal double foliation. It proves the compatibility of Horndeski Lagrangians with observations in an effective field theory approach. New solutions with intriguing logarithmic singularities and asymptotically nonflat behavior are derived, evading previous uniqueness theorems.
Article
Astronomy & Astrophysics
Soumya Chakrabarti, Amitabha Lahiri
Summary: In this study, an interacting scalar-fermion distribution is proposed to explain the cosmic acceleration in General Relativity. The model is supported by the generalized Om(z) parameter and comparison with observational data. Additionally, a toy model of unified cosmic expansion history is discussed, providing constraints on the scalar-fermion interaction profile and overall cosmological dynamics.
PHYSICS OF THE DARK UNIVERSE
(2022)
Article
Astronomy & Astrophysics
Nils Siemonsen, William E. East
Summary: The study shows that rotating scalar boson stars with m = 1 are always unstable, while adding nonlinear interactions to m = 1 boson stars may weaken this non-axisymmetric instability. Additionally, boson stars with m = 2 are unstable in all cases.
Article
Physics, Particles & Fields
Genly Leon, Esteban Gonzalez, Samuel Lepe, Claudio Michea, Alfredo D. Millano
Summary: Scalar-field cosmologies with a generalized harmonic potential and matter are investigated in different metrics, with a focus on global results. Different attractors are found for Kantowski-Sachs and closed Friedmann-Lemaitre-Robertson-Walker metrics, and the importance of time-averaged system in determining future asymptotics is highlighted.
EUROPEAN PHYSICAL JOURNAL C
(2021)
Article
Astronomy & Astrophysics
Bob Holdom
Summary: We explore singularity-free and geodesically-complete cosmologies based on manifolds that are not quite Lorentzian. The metric can be either smooth everywhere or non-degenerate everywhere, but not both, depending on the coordinate system. On such a manifold, the universe can transition between expanding and contracting without violation of standard energy conditions, and we obtain an extension of the Kasner vacuum solutions.
Article
Physics, Particles & Fields
William H. Pannell, Andreas Stergiou
Summary: In this study, the one-loop beta functions for systems of N-s scalars and N-f fermions interacting via a general potential are analyzed as tensorial equations in 4-epsilon dimensions. Two distinct bounds on combinations of invariants constructed from the couplings are derived and used to prove restrictions on the anomalous dimensions of the elementary fields. The concept of 'levels' of fixed points in scalar-fermion theories is introduced, and the stability properties of fixed points are examined.
JOURNAL OF HIGH ENERGY PHYSICS
(2023)
Article
Physics, Multidisciplinary
T. K. Kassenova, P. Yu Tsyba, O. Razina, R. Myrzakulov
Summary: This work examines the construction of a representation of braid group generators from vertex models with N-states, which offers a valuable approach for studying knot invariants. An algebraic formula is proposed to calculate the knot invariant when the knot components have different spins. The study presents a procedure for obtaining braid generator representations from three-partite vertex models and explores the invariant of multi-colored linked knots using these representations.
PHYSICA A-STATISTICAL MECHANICS AND ITS APPLICATIONS
(2022)
Article
Multidisciplinary Sciences
Zhanna Sagidullayeva, Gulgassyl Nugmanova, Ratbay Myrzakulov, Nurzhan Serikbayev
Summary: This paper studies the Kuralay equations and the integrable motion of space curves induced by these equations. The gauge equivalence between these two equations is established, and the simplest soliton solutions are presented using the Hirota bilinear method. The nonlocal and dispersionless versions of the Kuralay equations are considered, and some integrable generalizations and other related nonlinear differential equations are presented.
Article
Mathematics, Applied
Y. Myrzakulov, A. Sharlez, D. Kenzhalin, S. Myrzakul, G. Yergaliyeva
Summary: The article investigates cosmological solutions of the Starobinsky model in a flat inhomogeneous viscous Universe. It provides a brief overview of the F(R) theory of gravity and then focuses on the specific cosmological model of the Starobinsky F(R) = alpha R + beta R-2 model. The dynamics of the Hubble parameter H, viscosity, and time are analyzed, revealing a transition from accelerated expansion to instantaneous compression at a certain point in time, followed by a cessation of expansion.
INTERNATIONAL JOURNAL OF MATHEMATICS AND PHYSICS
(2022)
Article
Astronomy & Astrophysics
Damianos Iosifidis, Ratbay Myrzakulov, Lucrezia Ravera, Gulmira Yergaliyeva, Koblandy Yerzhanov
Summary: This study extends the previous research on quadratic Metric-Affine Gravity and investigates a new quadratic gravity action in vacuum. The research discusses the characteristics and cosmological aspects of the theory, as well as its implications in the context of F(R, T, Q, T, D) gravity.
PHYSICS OF THE DARK UNIVERSE
(2022)
Review
Astronomy & Astrophysics
V. K. Oikonomou, Pyotr Tsyba, Olga Razina
Summary: In this article, we discuss how Earth's climatological and geological history and the shadows of galactic black holes can provide insights into the past evolution of our universe. We propose that a pressure singularity in the universe's past may have affected Earth's history and the shadows of cosmological black holes. We explore the possibility of an abrupt physics change occurring 70-150 million years ago and its impact on Cepheid parameters. We also discuss how modified gravity, specifically F(R) gravity, can explain this evolution without the need for cosmic fluids or scalar fields.
Article
Physics, Mathematical
Yerlan Myrzakulov, Kairat Myrzakulov, Sudhaker Upadhyay, Dharm Veer Singh
Summary: In this paper, an exact regular black hole solution in the Einstein-Gauss-Bonnet theory coupled with nonlinear matter fields is presented. It is a generalization of a regular Einstein-Gauss-Bonnet black hole in 5D AdS spacetime. The obtained solution has the same causal structure as the Boulware-Deser black hole solution, except for the curvature singularity at the center. The solution incorporates the Boulware-Deser black holes in the absence of deviation parameters and satisfies a modified first law of thermodynamics. The stability of the black hole solution is discussed, revealing a double phase transition and the existence of critical points.
INTERNATIONAL JOURNAL OF GEOMETRIC METHODS IN MODERN PHYSICS
(2023)
Article
Physics, Multidisciplinary
Sudhaker Upadhyay, Surajit Mandal, Yerlan Myrzakulov, Kairat Myrzakulov
Summary: In this paper, we discuss the behavior of light in a charged black hole solution within the context of massive gravity. By analyzing the optical geometry of the black hole solution, we determine the Gaussian curvature in the weak gravitational lensing regime. Additionally, we investigate the deflection angle of light rays in both plasma and non-plasma media using the Gauss-Bonnet theorem. We also examine the implications of the Regge-Wheeler equation and derive strict bounds on the greybody factors of linearly charged massive BTZ black holes. Moreover, we study the shadow or silhouette produced by charged massive BTZ black holes, and explore the effects of charge and cosmological constant on the shadow radius.
Article
Physics, Nuclear
Surajit Mandal, Sudhaker Upadhyay, Yerlan Myrzakulov, Gulmira Yergaliyeva
Summary: In this paper, the authors discuss the shadow cast by the charged Reissner-Nordstrom (RN) anti-de Sitter (AdS) black hole. They calculate the geodesic equations for null particles using the Killing equation and Hamilton-Jacobi equation, and determine the celestial coordinates and shadow radius of the RN AdS black hole. The authors present a graphical analysis of the black hole shadow, showing it to be a perfectly dark circle. They also investigate the effects of charge, cosmological constant, and plasma medium on the shadow radius and energy emission rate of the RN AdS black hole.
INTERNATIONAL JOURNAL OF MODERN PHYSICS A
(2023)
Article
Physics, Particles & Fields
Prosenjit Paul, Sudhaker Upadhyay, Yerlan Myrzakulov, Dharm Veer Singh, Kairat Myrzakulov
Summary: In this paper, the authors investigate the thermodynamics of nonlinearly charged AdS black holes in four-dimensional critical gravity under the effect of small statistical fluctuations. They calculate the correction to the thermodynamics of these black holes at the leading order and discuss their stability under fluctuation. The authors also derive the isothermal and adiabatic compressibilities and study the impact of small fluctuations on the equation of states and the P - v diagram of the black holes.
Article
Physics, Multidisciplinary
S. A. Myrzakulova, O. Razina, N. A. Myrzakulov, A. B. Altaybaeva
Summary: In this paper, a periodic cosmological model is studied and the corresponding parameters and graphs are calculated. Additionally, the consistency of this model with previously proposed ones is explored. This has important implications for studying dark energy and cosmic expansion.
RECENT CONTRIBUTIONS TO PHYSICS
(2022)
Article
Physics, Multidisciplinary
D. Z. Rakhatov, P. Y. Tsyba, O. Razina
Summary: In this article, the Gauss-Bonnet model of gravity is investigated in a flat, isotropic and homogeneous universe. The solutions for the scale factor with power and modified power dependence on time are found using the method of variation. It is shown that the model satisfies the energy conditions but not the SEC. The parameters of the model correspond to modern cosmological data, confirming its realism in an accelerated expanding universe.
RECENT CONTRIBUTIONS TO PHYSICS
(2022)
Article
Physics, Multidisciplinary
G. S. Altayeva, O. Razina, P. Yu Tsyba
Summary: This paper analyzes a cosmological model that includes fermion field, scalar field, and vector field with Yukawa interaction. It investigates the contribution of different types of matter to the dynamics of the universe. The study shows that in a flat, homogeneous, and isotropic space-time, the coupling between fields can cause the accelerated expansion of the universe. By using cosmography and energy condition, the author obtained hybrid solutions for the cosmological equations. The analysis also relates the cosmographic parameters to the hybrid value of the scale factor and provides insights into the gravitational assumptions.
BULLETIN OF THE UNIVERSITY OF KARAGANDA-PHYSICS
(2022)
Article
Physics, Multidisciplinary
P. Yu Tsyba, O. Razina, N. T. Suikimbayeva
Summary: This paper examines models that combine modified Gauss-Bonnet gravity and general relativity to study the dynamics and energy conditions of the Universe. The study finds that the inclusion of higher-order invariants allows for additional degrees of freedom, and employing special functions to describe the change in the Hubble parameter leads to a quasi-Dieter law of scale factor evolution. The application of special equations of state and perturbation theory helps analyze the early and late stages of the Universe's evolution.
BULLETIN OF THE UNIVERSITY OF KARAGANDA-PHYSICS
(2022)
