Article
Astronomy & Astrophysics
David Benisty, Moshe M. Chaichian, Markku Oksanen
Summary: This passage studies the phenomenological implications of the Mimetic Tensor-Vector-Scalar theory (MiTeVeS). The theory extends the vector field model of mimetic dark matter by incorporating a scalar field, which is known to be ghost instability-free. When there is no interaction between the scalar field and the vector field, the obtained cosmological solution corresponds to the General Theory of Relativity (GR) with a minimally-coupled scalar field. However, introducing an interaction term between the scalar field and the vector field results in interesting dynamics.
PHYSICS OF THE DARK UNIVERSE
(2023)
Article
Physics, Particles & Fields
Ali H. Chamseddine
Summary: In this study, a supersymmetric version of gravity with mimetic dark matter was formulated, where a constrained chiral multiplet is coupled to N = 1 supergravity using tensor calculus rules. It was demonstrated that the system can spontaneously break supersymmetry, resulting in a model with a graviton, massive gravitino, and two scalar fields representing mimetic dark matter. The combination of the chiral multiplet and Lagrange multiplier multiplet was shown to act as the hidden sector breaking local N = 1 supersymmetry.
EUROPEAN PHYSICAL JOURNAL C
(2021)
Article
Physics, Particles & Fields
Federico Re
Summary: This research proposes a relativistic effect to explain dark matter and dark energy. Inhomogeneous matter generates gravitational distortions, significantly affecting the expansion of the universe and requiring corrections to the parameters of the standard cosmological model. Relativistic models offer various solutions, including those that fully explain dark energy and dark matter.
EUROPEAN PHYSICAL JOURNAL C
(2021)
Article
Astronomy & Astrophysics
Antonio De Felice, Shinji Mukohyama
Summary: This paper introduces a new cosmological framework integrating dark matter into a minimally modified gravity model, maintaining the same number of gravitational degrees of freedom through a series of transformations. The framework includes two time-dependent free functions to achieve desired evolutions of Hubble expansion rate and effective gravitational constant for dark matter.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Astronomy & Astrophysics
V. K. Oikonomou, F. P. Fronimos, Pyotr Tsyba, Olga Razina
Summary: Under the assumption that the axion scalar field forms the dark matter in the Universe, this paper extends the formalism of kinetic axion R2 gravity to include non-minimally coupled Gauss-Bonnet terms. It is shown that this Gauss-Bonnet term has significant effects on inflationary phenomenology and the kinetic axion scenario. Unlike in kinetic axion R2 gravity, the Gauss-Bonnet corrected kinetic axion R2 gravity leads to a non-extended inflationary era and immediate commencement of reheating driven by R2 fluctuations.
PHYSICS OF THE DARK UNIVERSE
(2023)
Article
Astronomy & Astrophysics
Miguel Aparicio Resco, Antonio L. Maroto
Summary: The study analyzes how to parametrize general modifications of the dark matter perturbations equations in a model-independent way, and shows that a general model with an imperfect and non-conserved dark matter fluid in a modified gravity scenario can be described with five general functions. It focuses on the sub-Hubble regime and finds that observable power spectra are sensitive to only three combinations of the initial five functions, which can help determine whether a modification of gravity or an imperfect/non-conserved dark matter is present. A Fisher forecast analysis for these three parameters is performed, with an example shown for a specific model with shear viscosity.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Astronomy & Astrophysics
Hooman Davoudiasl, Peter B. Denton, David A. McGady
Summary: The conventional lore excludes fermionic dark matter with mass lighter than a few hundred electronvolts based on the Pauli exclusion principle. A new method is proposed in this paper which involves numerous quasi-degenerate species of fermions without couplings to the standard model to evade this bound. Gravitational interactions impose constraints from measurements at the LHC, cosmic rays, supernovae, and black hole spins and lifetimes, with a particular limit on the number of distinct species of particles being less than or around 10^62.
Article
Physics, Particles & Fields
Yogendra Srivastava, Giorgio Immirzi, John Swain, Orlando Panella, Simone Pacetti
Summary: This article discusses a general class of axially symmetric metrics in general relativity that includes rotations, which are used to study the dynamics of rotationally supported galaxies. The exact vacuum solutions of the Einstein equations for this extended Weyl class of metrics lead to the following rigorous deductions: (i) The rotational velocity in general relativity always exceeds the Newtonian velocity due to Lenz's law. (ii) A non-zero intrinsic angular momentum for a galaxy requires the asymptotic constancy of the Weyl length parameter, similar to the Kerr metric. (iii) The asymptotic constancy of the parameter also implies a plateau in the rotational velocity. Unlike the Kerr metric, the extended Weyl metric can be extended within the galaxy, and it has been shown that Gauss and Ampere laws emerge along with Ludwig's extended gravito-electromagnetism (GEM) theory and non-linear rate equations for the velocity field. More accurate estimates for the Sun's escape velocity than those obtained from Newtonian theory have been presented.
EUROPEAN PHYSICAL JOURNAL C
(2023)
Article
Astronomy & Astrophysics
Alvaro de la Cruz Dombriz, Francisco Jose Maldonado Torralba, David F. Mota
Summary: The stable pseudo-scalar degree of freedom in the quadratic Poincare Gauge theory of gravity is identified as a suitable candidate for dark matter. The study determines the parameter space in the theory that can explain all predicted cold dark matter phenomena and constrains these parameters with astrophysical observations.
Article
Physics, Multidisciplinary
Anirban Chatterjee, Biswajit Jana, Abhijit Bandyopadhyay
Summary: This paper investigates the dynamics of a homogeneous k-essence scalar field that drives dark energy and demonstrates that even with time-dependent interactions between dark energy and dark matter, the constancy of the k-essence potential can lead to a modified scaling relation.
EUROPEAN PHYSICAL JOURNAL PLUS
(2022)
Article
Physics, Multidisciplinary
Mikhail Shaposhnikov, Andrey Shkerin, Inar Timiryasov, Sebastian Zell
Summary: This passage discusses a novel mechanism for producing singlet fermions in the early Universe through gravity-induced interactions. These fermions can act as dark matter particles and are applicable to a wide range of dark matter particle masses. The potential observational consequences of producing keV-scale dark matter in this way, particularly for right-handed neutrinos, are also explored. The authors suggest that determining the momentum distribution of primordial dark matter may shed light on gravity-induced fermionic interactions.
PHYSICAL REVIEW LETTERS
(2021)
Article
Astronomy & Astrophysics
Qing-Yang Wang, Yong Tang, Yue-Liang Wu
Summary: Dark matter and inflation are crucial in understanding the origin of cosmic structures. The Weyl scaling invariant theory of gravity provides a possible solution, where dark matter is represented by a massive gauge boson and inflation is achieved through R2. We investigate the production of dark matter in the Weyl R2 model and identify three viable parameter regions.
Article
Astronomy & Astrophysics
P. H. R. S. Moraes, G. Panotopoulos, I Lopes
Summary: This study investigates the properties of exotic stars made entirely of dark matter, considering intrinsic anisotropies that have been ignored so far. Semi-analytical solutions to the structure equations are obtained, showing that these solutions behave well within general relativity and can describe realistic astrophysical configurations. A direct comparison with isotropic counterparts with the same radius reveals that the latter are slightly more massive.
Article
Astronomy & Astrophysics
R. Mauland, O. Elgaroy
Summary: This research investigates the size and impact of vortices in a Superfluid Dark Matter (SFDM) model as well as explores the parameter space of the model. It is found that the vortices have a small size and are closely spaced. Varying the parameters of the model reveals that reducing the dark matter particle mass results in larger and more energetic vortices. However, none of the parameter combinations explored here produce vortices with both realistic values and enough energy to have an observational impact on the galaxy as a whole.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Physics, Particles & Fields
Zahra Haghani
Summary: The theory considers the growth rate of matter perturbations in the Einstein dark energy theory, with three fixed points. Due to the presence of the trace of the energy-momentum tensor, these fixed points occur at different locations compared to the Lambda CDM theory.
EUROPEAN PHYSICAL JOURNAL C
(2021)
Article
Physics, Multidisciplinary
V. K. Oikonomou
Summary: This study focuses on k-inflation theories with non-minimal coupling of the scalar field to gravity, investigating the evolution of the scalar field under slow-roll or constant-roll conditions when a scalar potential is present or absent. The results show that the theory is compatible with the latest Planck data in the slow-roll models with scalar potential, but less appealing in models without potential. Additionally, it is suggested that the Einstein frame counterpart of non-minimal k-inflation models with scalar potential may be a viable theory due to the conformal invariance of the observational indices.
EUROPEAN PHYSICAL JOURNAL PLUS
(2021)
Article
Astronomy & Astrophysics
A. V. Astashenok, S. Capozziello, S. D. Odintsov, V. K. Oikonomou
Summary: Investigated the causal limit of maximum mass for stars in the framework of f(R) gravity, numerically examining the combined effect of causal equation of state and sound speed on maximum mass of static neutron stars. This provides the most extreme upper bound for neutron star masses in extended gravity.
Article
Astronomy & Astrophysics
S. D. Odintsov, V. K. Oikonomou
Summary: This work examines the implications of a subclass of E-models cosmological attractors, known as a-attractors, on hydrodynamically stable slowly rotating neutron stars. By numerically solving the Tolman-Oppenheimer-Volkoff equations in the Einstein frame, the study finds that the masses and radii of neutron stars vary with the parameter a characterizing the a-attractors. Results indicate a complex relationship between non-minimal inflationary attractors and neutron star phenomenology in scalar-tensor theory.
PHYSICS OF THE DARK UNIVERSE
(2021)
Article
Physics, Multidisciplinary
V. K. Oikonomou
Summary: This study introduces a new theoretical framework of power-law f(R) gravity corrected canonical scalar field inflation and examines the inflationary dynamics of this new framework. The main characteristic is the dominance of a power-law f(R) gravity term, compared to the Einstein-Hilbert term, with good agreement with the latest Planck data for a wide range of free parameters. The resulting theory allows for viable inflationary theories which may otherwise be non-viable.
Article
Astronomy & Astrophysics
V. K. Oikonomou
Summary: In this work, a refined Einstein-Gauss-Bonnet inflationary theoretical framework is provided, which is compatible with observational constraints on the gravitational wave speed. By introducing new assumptions and conditions, much simpler expressions for the slow-roll indices, tensor and scalar spectral indices, and tensor-to-scalar ratio are successfully derived. A particular model with a blue-tilted tensor spectral index is exemplified, showing compatibility with the latest Planck data and potential to describe the NANOGrav result according to recent literature.
CLASSICAL AND QUANTUM GRAVITY
(2021)
Article
Astronomy & Astrophysics
V. K. Oikonomou
Summary: This study focuses on static neutron stars within a specific class of non-minimally coupled inflationary potentials, known as universal attractors. The analysis reveals that all studied cases predict larger maximum masses for neutron stars and are consistent with the GW170817 constraints on neutron star radii.
CLASSICAL AND QUANTUM GRAVITY
(2021)
Article
Physics, Multidisciplinary
A. Astashenok, S. Capozziello, S. D. Odintsov, V. K. Oikonomou
Summary: Novel implications on neutron stars come from extended gravity. Specifically, new research suggests the possibility of large mass stars in the mass gap region, which may require extensions of General Relativity to successfully describe this phenomenon and speculate on the largest allowed neutron star mass in a quantitative manner.
Article
Physics, Particles & Fields
G. G. L. Nashed, S. D. Odintsov, V. K. Oikonomou
Summary: This paper investigates spherically symmetric spacetime solutions that describe the interior of compact stellar objects within the context of higher-order curvature theory of the f(R) type. By deriving the non-vacuum field equations and solving the system of nonlinear differential equations, the study successfully identifies a specific solution for compact stars. Furthermore, the model is shown to be more stable and different from those in general relativity, with specific implications for the considered compact star Her X-1.
EUROPEAN PHYSICAL JOURNAL C
(2021)
Article
Physics, Mathematical
V. K. Oikonomou, Achilles Gitsis, Maria Mitrou
Summary: This study focuses on the phase space singularities of interactive quintessence model in the presence of matter fluid. The presence of matter fluid affects the dynamical system, making the singularities depend on initial conditions rather than occurring for general initial conditions.
INTERNATIONAL JOURNAL OF GEOMETRIC METHODS IN MODERN PHYSICS
(2021)
Review
Multidisciplinary Sciences
Sergei D. Odintsov, Vasilis K. Oikonomou, Ratbay Myrzakulov
Summary: In this work, the authors exhaustively study the effects of modified gravity on the energy spectrum of the primordial gravitational waves background. They provide calculations for various cases of modified gravity, focusing on specific forms of interest. They also present the exact form of a parameter involved in the calculation of the effects of modified gravity on the energy spectrum for the first time.
Article
Astronomy & Astrophysics
Sergei D. Odintsov, Tanmoy Paul
Summary: This work explores the influence of a Type-IV singularity on the dynamics of a bouncing universe in the context of a ghost-free Gauss-Bonnet theory of gravity. It is found that when the singularity has a global effect on spacetime, the scalar power spectrum becomes red-tilted and the tensor-to-scalar ratio is incompatible with observational data. However, if the singularity only locally affects spacetime around the time of occurrence, the observable quantities are compatible with Planck data.
Editorial Material
Multidisciplinary Sciences
Sergei D. D. Odintsov
Editorial Material
Multidisciplinary Sciences
Sergei D. Odintsov
Article
Multidisciplinary Sciences
Artyom V. Astashenok, Sergey D. Odintsov, Vasilis K. Oikonomou
Summary: This study investigates the Chandrasekhar mass limit of white dwarfs in various models of f (R) gravity. Two equations of state for stellar matter are used: the simple relativistic polytropic equation and the realistic Chandrasekhar equation of state. The solution for any model of f (R) = R + beta R-m gravity shows that the stellar mass decreases compared to standard General Relativity. For realistic equations of state, there is a value of the central density for which the mass of a white dwarf peaks. This implies that in modified gravity, there exists a minimum radius for stable white dwarfs, which is greater than in General Relativity. The behavior of the Chandrasekhar mass limit in f (R) gravity is also investigated.
Article
Astronomy & Astrophysics
V. K. Oikonomou
Summary: In this study, we analyze the scenario where the effective gravitational Lagrangian of a minimally coupled scalar field becomes a rescaled Einstein-Hilbert gravity at large curvatures, leading to changes in the inflationary phenomenology and satisfaction of swampland criteria. Two inflation models, fiber inflation and supergravity alpha-attractor models, are discussed to show their viability and satisfaction of swampland criteria. The late-time phenomenology of the fiber inflation potential in the presence of full f(R) gravity is examined, showing the production of a viable dark energy era similar to the Lambda-cold-dark-matter model. The modified gravity model presents a universe described by a rescaled Einstein-Hilbert gravity at early times, with the scalar field mainly controlling dynamics synergistically with f(R) gravity at late times.
