arXiv subjects

Tiberiu Harko

Publications and source records attributed to Tiberiu Harko.

At least 37 records · Page 2Linked to original sources

arXiv2025

Bose-Einstein Condensate dark matter with logarithmic nonlinearity

If dark matter is composed of massive bosons, a Bose-Einstein Condensation process must have occurred during the cosmological evolution. Therefore, galactic dark matter may be in a form of a self-gravitating condensate, in the presence of self-interactions. We consider the possibility that the self-interacting potential of the condensate dark matter is of the logarithmic form. In order to describe the condensate dark matter we use the Gross-Pitaevskii equation with a logarithmic nonlinearity, and the Thomas-Fermi approximation. With the use of the hydrodynamic representation of the Gross-Pitaevskii equation we obtain the equation of state of the condensate, which has the form of the ideal gas equation of state, with the pressure proportional to the dark matter density. The basic equation describing the density distribution of the static condensate is derived, and its solution is obtained in the form of a series solution, constructed with the help of the Adomian Decomposition Method. To test the model we consider the properties of the galactic rotation curves in the logarithmic Bose-Einstein Condensate dark matter scenario, by using a sample from the Spitzer Photometry and Accurate Rotation Curves (SPARC) data. The fit of the theoretical predictions of the rotation curves with the observational data indicate that the logarithmic Bose-Einstein Condensate dark matter model gives an acceptable description of the SPARC data, and thus it may be considered as a possible candidate for the in depth understanding of the dark matter properties.

gr-qc↗

arXiv2025

Schrödinger-type $f(Q,T)$ gravity-nonmetricity driven cosmological evolution from inflation to the late Universe

We consider an $f(Q, T)$ gravity theory with a Schrödinger type vectorial non-metricity. In the presence of such a non-metricity, the length of vectors is preserved under autoparallel transport. We obtain the field equations assuming a vanishing total scalar curvature, implemented by a Lagrange multiplier, and investigate their cosmological implications. To do this, we derive the generalized Friedmann equations which now have terms involving the non-metricity and the Lagrange multiplier. Then, we consider two distinct cosmological applications of the model. First of all, by adopting distinct forms of these two basic variables and investigate the possibility of the existence of warm inflationary scenarios within the framework of these models. In particular, we consider the case that the non-metricity is described by a constant vector, and we show that with this assumption we recover standard general relativity. The scenario in which the Lagrange multiplier is a constant is also investigated, and we show that radiation can be created during the very early phases of expansion. The amount of radiation peaks at a certain time after which, there is a transition from an accelerating inflationary phase to a decelerating one. Moreover, we perform a detailed comparison of the predictions of the considered Schrödinger type cosmology with a set of observational data for the Hubble function, including Cosmic Chronometers, Type Ia Supernovae, and Baryon Acoustic Oscillations, using a Markov Chain Monte Carlo (MCMC) analysis, by adopting a simple linear form for the Lagrange density. The model predictions are also compared with the results of the $Λ$CDM standard paradigm. Our results indicate that the Schrödinger $f(Q,T)$ type theory can give a good description of the observational data for both the very early and the late Universe.

gr-qc↗

arXiv2025

Observational tests of the conformal osculating Barthel-Kropina cosmological model

We consider detailed cosmological tests of dark energy models obtained from the general conformal transformation of the Kropina metric, representing an $(α,β)$-type Finslerian geometry. In particular, we restrict our analysis to the osculating Barthel Kropina geometry. The Kropina metric function is defined as the ratio of the square of a Riemannian metric $α$ and of the one-form $β$. In this framework, we also consider the role of the conformal transformations of the metric, which allows us to introduce a family of conformal Barthel-Kropina theories in an osculating geometry. The models obtained in this way are described by second-order field equations, in the presence of an effective scalar field induced by the conformal factor. The generalized Friedmann equations of the model are obtained by adopting for the Riemannian metric $α$ the Friedmann Lemaitre Robertson Walker representation. In order to close the cosmological field equations, we assume a specific relationship between the component of the one-form $β$ and the conformal factor. With this assumption, the cosmological evolution is determined by the initial conditions of the scalar field and a single free parameter $γ$ of the model. The conformal Barthel Kropina cosmological models are compared against several observational datasets, including Cosmic Chronometers, Type Ia Supernovae, and Baryon Acoustic Oscillations, using a Markov Chain Monte Carlo (MCMC) analysis, which allows the determination of $γ$. A comparison with the predictions of standard $Λ$CDM model is also performed. {Our results indicate that the conformal osculating Barthel Kropina model can be considered as a successful, and simple, alternative to standard cosmological models.

gr-qc↗

arXiv2025

Modified Gravity with Nonminimal Curvature-Matter Couplings: A Framework for Gravitationally Induced Particle Creation

Modified gravity theories with a nonminimal coupling between curvature and matter offer a compelling alternative to dark energy and dark matter by introducing an explicit interaction between matter and curvature invariants. Two of the main consequences of such an interaction are the emergence of an additional force and the non-conservation of the energy--momentum tensor, which can be interpreted as an energy exchange between matter and geometry. By adopting this interpretation, one can then take advantage of many different approaches in order to investigate the phenomenon of gravitationally induced particle creation. One of these approaches relies on the so-called irreversible thermodynamics of open systems formalism. By considering the scalar--tensor formulation of one of these theories, we derive the corresponding particle creation rate, creation pressure, and entropy production, demonstrating that irreversible particle creation can drive a late-time de Sitter acceleration through a negative creation pressure, providing a natural alternative to the cosmological constant. Furthermore, we demonstrate that the generalized second law of thermodynamics holds: the total entropy, from both the apparent horizon and enclosed matter, increases monotonically and saturates in the de Sitter phase, imposing constraints on the allowed particle production dynamics. Furthermore, we present brief reviews of other theoretical descriptions of matter creation processes. Specifically, we consider approaches based on the Boltzmann equation and quantum-based aspects and discuss the generalization of the Klein--Gordon equation, as well as the problem of its quantization in time-varying gravitational fields.

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arXiv2025

The Weyl Geometric Gravity black hole in light of the Solar System tests

The Weyl geometric gravity theory, in which the gravitational action is constructed from the square of the Weyl curvature scalar and the strength of the Weyl vector, has been intensively investigated recently. The theory admits a scalar-vector-tensor representation, obtained by introducing an auxiliary scalar field, and can therefore be reformulated as a scalar-vector-tensor theory in a Riemann space, in the presence of a nonminimal coupling between the Ricci scalar and the scalar field. By assuming that the Weyl vector has only a radial component, an exact spherically symmetric vacuum solution of the field equations can be obtained, which depends on three integration constants. As compared to the Schwarzschild solution, the Weyl geometric gravity solution contains two new terms, linear and quadratic in the radial coordinate, respectively. In the present work we consider the possibility of testing and obtaining observational restrictions on the Weyl geometric gravity black hole at the scale of the Solar System, by considering six classical tests of general relativity (gravitational redshift, the Eötvös parameter and the universality of free fall, the Nortvedt effect, the planetary perihelion precession, the deflection of light by a compact object, and the radar echo delay effect, respectively) for the exact spherically symmetric black hole solution of the Weyl geometric gravity. All these gravitational effects can be fully explained and are consistent with the vacuum solution of the Weyl geometric gravity. Moreover, the study of the classical general relativistic tests also allows to constrain the free parameter of the solution.

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arXiv2025

Big Bang Nucleosynthesis constraints on space-time noncommutativity

We consider the implications of the modified dispersion relations, due to the noncommutativity of the spacetime, for a photon gas filling the early Universe in the framework of the Big Bang Nucleosynthesis (BBN) processes, during the period of light elements formation. We consider three types of deformations present in the dispersion relations for the radiation gas, from which we obtain the low temperature corrections to the energy density and pressure. The cosmological implications of the modified equations of state in the BBN era are explored in detail for all radiation models. The effects induced on the nucleosynthesis process by spacetime noncommutativity are investigated by evaluating the abundances of relic nuclei (Hydrogen, Deuterium, Helium-3, Helium-4, and Lithium-7). The primordial mass fraction estimates and their deviations due to changes in the freezing temperature impose an upper limit on the energy density of the deformed photon gas, which follows from the modified Friedmann equations. The deviations from the standard energy density of the radiative plasma are therefore constrained by the abundances of the Helium-4 nuclei. Upper limits on the free parameters of the spacetime noncommutativity are obtained via a numerical analysis performed using the \texttt{PRyMordial} software package. The primordial abundances of the light elements are obtained by evaluating the thermonuclear reaction rates for the considered noncommutative spacetime models. An MCMC (Markov Chain Monte Carlo) analysis allows to obtain restrictions on the free parameters of the modified dispersion relations. The numerical and statistical approach is implemented in the python code \texttt{PRyNCe}, available on GitHub.

gr-qc↗

arXiv2025

The Stochastic-Dissipative Störmer Problem-Trajectories and Radiation Patterns

We consider a generalization of the classical nonrelativistic Störmer problem, describing the motion of charged particles in a purely magnetic dipole field, by taking into account the effects of the dissipation, assumed to be of friction type, proportional to the velocity of the particle, and of the presence of stochastic forces. In the presence of dissipative/stochastic effects, the motion of the particle in the magnetic dipole field can be described by a generalized Langevin type equation, which generalizes the standard Lorentz force equation. We perform a detailed numerical analysis of the dynamical behavior of the particles in a magnetic dipolar field in the presence of dissipative and stochastic forces, as well as of the electromagnetic radiation patterns emitted during the motion. The effects of the dissipation coefficient and of the stochastic force on the particle motion and on the emitted electromagnetic power are investigated, and thus a full description of the spectrum of the magnetic dipole type electromagnetic radiation and of the physical properties of the motion is also obtained. The power spectral density of the emitted electromagnetic power is also obtained for each case, and, for all considered Störmer type models, it shows the presence of peaks in the radiation spectrum, corresponding to certain intervals of the frequency.

astro-ph.HE↗

arXiv2025

Gravitational properties of Bose-Einstein condensate dark matter halos

Recent studies suggest that dark matter could take the form of a Bose-Einstein condensate (BEC), a possibility motivated by anomalies in galactic rotation curves and the missing mass problem in galaxy clusters. We investigate the astrophysical properties of BEC dark matter halos and their potential observational signatures distinguishing them from alternative models. In this framework, dark matter behaves as a self-gravitating Newtonian fluid with a polytropic equation of state of index $n=1$. We derive analytic expressions for the mass distribution, gravitational potential, and dynamical profiles such as the density slope and tangential velocity. The lensing behavior of BEC halos is analyzed, yielding a general series representation of the projected surface density that enables precise predictions for deflection angles, lensing potentials, and magnifications. Finally, halo equilibrium and stability are examined via the scalar and tensor virial theorems, leading to perturbation equations that describe their response to small disturbances. Together, these results provide a unified framework linking the microscopic physics of condensate dark matter to macroscopic halo observables.

gr-qc↗

arXiv2025

$f(Q,L_m)$ gravity, and its cosmological implications

Symmetric teleparallel gravity and its $f(Q)$ extensions have emerged as promising alternatives to General Relativity (GR), yet the role of explicit geometry-matter couplings remains largely unexplored. In this work, we address this gap by proposing a generalized $f(Q,\mathcal{L}_m)$ theory, where the gravitational Lagrangian density depends on both the non-metricity scalar $Q$ and the matter Lagrangian $\mathcal{L}_m$. This formulation naturally includes Coincident GR and the Symmetric Teleparallel Equivalent of GR as special cases. Working in the metric formalism, we derive the corresponding field equations, which generalize those of the standard $f(Q)$ gravity, and obtain the modified Klein-Gordon equation for scenarios involving scalar fields. The cosmological implications of the theory are explored in the context of the Friedmann-Lemaitre-Robertson-Walker (FLRW) universe. As a first step, we obtain the modified Friedmann equations for $f(Q,\mathcal{L}_m)$ gravity in full generality. We then investigate specific cosmological models arising from both linear and non-linear choices of $f(Q,\mathcal{L}_m)$, performing detailed comparisons with the standard $Λ$CDM scenario and examining their observational consequences.

gr-qc↗

arXiv2025

Big Bang Nucleosynthesis constraints on the cosmological evolution in a Universe with a Weylian Boundary

We investigate the effects that arise from the inclusion of Weylian boundary terms in the Einstein gravitational field equations in the Big Bang Nucleosynthesis (BBN) framework. With the help of the generalized Friedmann equations for a Universe with a Weylian boundary, obtained for a Friedmann-Lemaitre-Robertson-Walker FLRW metric, three distinct cosmological models can be constructed. The cosmological evolution is determined by a dissipative scalar field, and by the Weyl vector coming from the boundary. Several cosmological scenarios are obtained via the appropriate splitting of the generalized energy conservation equation. In the present work we obtain relevant constraints on these models by using the BBN data. In particular, the effects on the BBN that arise in the post warm-inflationary era will be examined by theoretically evaluating the measured abundances of relic nuclei (Hydrogen, Deuterium, Helium-3, Helium-4, and Lithium-7). We consider firstly the primordial mass fraction estimates, and their deviations due to changes in the freezing temperature, which impose an upper limit on the effective energy density obtained from the modified Friedmann equations. The deviation from the standard energy density of the radiative plasma is therefore constrained by the abundances of the Helium-4 nuclei. Secondly, an upper limit will be considered in a numerical analysis performed through the usage of the \texttt{PRyMordial} software package, with the help of which we calculate the primordial abundances of the light elements by evaluating the thermonuclear rates within the considered modified gravity framework. Finally, an MCMC analysis will validate the cosmological model with Weylian boundary contributions, imposing relevant constraints on the initial conditions of the cosmos. The methodology is implemented in the python code \texttt{genesys}, which is available on GitHub.

gr-qc↗

arXiv2025

From Barthel Randers Kropina Geometries to the Accelerating Universe: A Brief Review of Recent Advances in Finslerian Cosmology

We review recent developments in cosmological models based on Finsler geometry and extensions of general relativity within this framework. Finsler geometry generalizes Riemannian geometry by allowing the metric tensor to depend on position and an additional internal degree of freedom, typically represented by a vector field at each point of the spacetime manifold. We explore whether Finsler-type geometries can describe gravitational interaction and cosmological dynamics. In particular, we examine the Barthel connection and $(α, β)$ geometries, where $α$ is a Riemannian metric and $β$ is a one-form. For a specific construction of $β$, the Barthel connection coincides with the Levi-Civita connection of the associated Riemann metric. We review gravitational field and cosmological evolution in three geometries: Barthel-Randers ($F = α+ β$), Barthel-Kropina ($F = α^2 β$), and the conformally transformed Barthel-Kropina geometry. After presenting the mathematical foundations of Finslerian-type modified gravity theories, we derive generalized Friedmann equations in these geometries assuming a Friedmann-Lemaître-Robertson-Walker type metric. We also present the matter-energy balance equations, interpreting them from the perspective of thermodynamics with particle creation. The cosmological properties of Barthel-Randers and Barthel-Kropina models are explored in detail. The additional geometric terms in these models can be interpreted as an effective dark energy component, generating an effective cosmological constant. Several cosmological solutions are compared with observational data (Cosmic Chronometers, Type Ia Supernovae, Baryon Acoustic Oscillations) using MCMC analysis. A comparison with the $Λ$CDM model shows that Finslerian models fit observational data well, suggesting they offer a viable alternative to general relativity.

gr-qc↗

arXiv2025

f(R, $G$, T) Gravity: Cosmological Implications and Dynamical System Analysis

We consider the cosmological implications of a four-dimensional extension of the Gauss-Bonnet $f(G)$ gravity, where $G$ is the Gauss-Bonnet topological invariant, in which the Einstein-Hilbert action is replaced by an arbitrary function $f(R,G,T)$ of G, of the Ricci scalar $R$, and of the trace $T$ of the matter energy-momentum tensor. By construction, the extended Gauss-Bonnet type action involves a non-minimal coupling between matter and geometry. The field equations of the model are obtained by varying the action with respect to the metric. The generalized Friedmann equations, describing the cosmological evolution in the flat Friedmann-Lemaitre-Robertson-Walker geometry, are also presented in their general form. We investigate the cosmological evolution of the Universe in the generalized Einstein-Gauss-Bonnet theiry for a specific choice of the Lagrangian density, as given by $f(R,G,T) = α_1 G^{m} + α_2 R^β - 2α_3 \sqrt{-T},$ where $α_i$ $ i = 1, 2, 3$), $ m $, and $β$ are model parameters. First, the theoretical predictions of the model are compared with a set of observational data (Cosmic Chronometers, Type IA Supernovae, Baryon Acoustic Oscillations) via an MCMC analysis, which allows us to obtain constraints on the model parameters. A comparison with the predictions of the $Λ$CDM system is also performed. Next, the generalized Friedmann equations are reformulated as a dynamical system, and the properties of its critical points are studied by using the Lyapunov linear stability analysis. This investigation allows for the reconstruction of the Universe's history in this model, from the early inflationary era to the late accelerating phase. The statefinder diagnostic parameters for the model are also considered from the dynamical system perspective.

gr-qc↗

arXiv2025

Charged black hole solutions in $f(R,T)$ gravity coupled to nonlinear electrodynamics

In this work, we investigate static and spherically symmetric black hole solutions in $f(R,T)$ gravity, where $R$ is the curvature scalar and $T$ is the trace of the energy-momentum tensor, coupled to nonlinear electrodynamics (NLED). To construct our solutions, we adopt a linear functional form, $f(R,T) = R + βT$. In the limit $β= 0$, the theory reduces to General Relativity (GR), recovering $f(R,T) \approx R$. We propose a power-law Lagrangian of the form $\mathcal{L} = f_0 + F + αF^p$, where $α=f_0= 0$ corresponds to the linear electrodynamics case. Using this setup, we derive the metric functions and determine an effective cosmological constant. Our analysis focuses on specific cases with $p = 2$, $p = 4$, and $p = 6$, where we formulate analytic expressions for the matter fields supporting these solutions in terms of the Lagrangian as a function of $F$. Additionally, we verify the regularity of the solutions and study the structure of the event horizons. Furthermore, we examine a more specific scenario by determining the free forms of the first and second derivatives $\mathcal{L}_F(r)$ and $\mathcal{L}_{FF}(r)$ of the Lagrangean of the nonlinear electromagnetic field. From these relations, we derive the general form of $\mathcal{L}_{\text{NLED}}(r)$ using consistency relations. This Lagrangian exhibits an intrinsic nonlinearity due to the influence of two constants, $α$ and $β$. Specifically, $α$ originates from the power-law term in the proposed Lagrangian, while $β$ arises from the assumed linear function $f(R,T)$. The interplay of these constants ensures that the nonlinearity of the Lagrangian is governed by both $α$ and $β$, rather than $α$ alone.

gr-qc↗

arXiv2025

Matter really does matter, or Why $f(R,{\rm Matter})$ type theories are significant for gravitational physics and cosmology

In a recent paper (Lacombe, Mukohyama, and Seitz, JCAP {\bf 2024}, 05, 064 (2024)), the authors provided an in-depth analysis of a class of modified gravity theories, generally called $f(R,{\rm Matter})$ theories, which assume the existence of a non-minimal coupling between geometry and matter. It was argued that if the matter sector consists of Standard Model particles, then these theories suffer from the presence of ghosts, or are just scalar/vector-tensor theories. Hence, the relevance of these theories for cosmology was questioned. It is the goal of the present work to carefully analyze, discuss, and assess the line of arguments proposed in Lacombe et al. JCAP {\bf 2024}, 05, 064 (2024). After a qualitative critical discussion of the five general arguments proposed for the validity of a gravitational theory, we present the theoretical foundations of the $f(R,{\rm Matter})$ theories, including their possible relations with quantum gravity, and discuss in detail the role of matter. The matter source discussed in Lacombe et al., consisting predominantly of a massless scalar field, is extremely restrictive, and rather irrelevant for cosmology and the description of the observational data. We also devote a detailed discussion of the problem of the energy scales of the $f(R,{\rm Matter})$ theories. To test the observational relevance of this type of theories we present the comparison of a simple theoretical model with a small set of observational data and with the $Λ$CDM paradigm. We conclude by pointing out that the analysis of Lacombe et al., JCAP {\bf 2024}, 05, 064 (2024), even very useful for the understanding of some limited aspects of the $f(R,{\rm Matter})$ theories, and of their theoretical foundations, cannot be considered as a valid or definite criticism of these approaches to gravity.

gr-qc↗

arXiv2025

Mimetic Weyl geometric gravity

We consider a mimetic type extension of the Weyl geometric gravity theory, by assuming that the metric of the space-time manifold can be parameterized in terms of a scalar field, called the mimetic field. The action of the model is obtained by starting from a conformally invariant gravitational action, constructed, in Weyl geometry, from the square of the Weyl scalar, the strength of the Weyl vector, and an effective matter term, respectively. after linearizing the action in the Weyl scalar by introducing an auxiliary scalar field, we include the mimetic field, constructed from the same auxiliary scalar field used to linearize the action, via a Lagrange multiplier. The conformal invariance of the action is maintained by imposing the trace condition on the effective matter energy-momentum tensor, built up from the ordinary matter Lagrangian, and some specific functions of the Weyl vector, and the scalar field, respectively, thus making the matter sector of the action conformally invariant. We investigate the cosmological implications of the Mimetic Weyl geometric gravity by considering the dynamics of an isotropic and homogeneous FRW Universe. The generalized Friedmann equations of the model are derived, and their solutions are obtained numerically for a dust filled Universe. Moreover, we perform a detailed comparison of the predictions of the considered model with a set of observational data for the Hubble function, and with the results of the $Λ$CDM standard paradigm. Our results indicate that the present model give a good description of the observational data, and they reproduce almost exactly the predictions of the $Λ$CDM scenario. Hence, Mimetic Weyl geometric gravity can be considered a viable alternative to the standard approaches to cosmology, and to the gravitational phenomena.

gr-qc↗

arXiv2025

Length-preserving biconnection gravity and its cosmological implications

We consider a length-preserving biconnection gravitational theory, inspired by information geometry, which extends general relativity by using the mutual curvature as the fundamental object describing gravity. The two connections used to build up the theory are the Schrödinger connection, and its dual. It can be seen that the dual of a non-metric Schrödinger connection possesses torsion, even if the Schrödinger connection itself does not, and consequently the pair $(M,g,\nabla^{*})$ is a quasi-statistical manifold. The field equations are postulated to have the form of the standard Einstein equations, but with the Ricci tensor- and scalar replaced with the mutual curvature tensor- and scalar, resulting in additional torsion-dependent terms. The covariant divergence of the matter energy-momentum does not vanish in this theory. We derive the equation of motion for massive particles, which shows the presence of an extra force. The Newtonian limit of the equations of motion is also considered. We explore the cosmological implications by deriving the generalized Friedmann equations for the FLRW geometry. They contain additional terms that can be interpreted as describing an effective, geometric type dark energy. We examine two cosmological models: one with conserved matter, and one where dark energy and pressure are related by a linear equation of state. The predictions of both models are compared with a set of observational values of the Hubble function, and with the standard $Λ$CDM model. Length-preserving biconnection gravity models fit well the observational data, and also align with $Λ$CDM at low redshifts $(z<3)$. The obtained results suggest that a modified biconnection geometry could explain the late-time acceleration, as well as the formation of the supermassive black holes, since they predict a different age of our Universe as compared to standard cosmology.

gr-qc↗

arXiv2024

The first variation of the matter energy-momentum tensor with respect to the metric, and its implications on modified gravity theories

The first order variation of the matter energy-momentum tensor $T_{μν}$ with respect to the metric tensor $g^{αβ}$ plays an important role in modified gravity theories with geometry-matter coupling, and in particular in the $f(R,T)$ modified gravity theory. We obtain the expression of the variation $δT_{μν}/δg^{αβ}$ for the baryonic matter described by an equation given in a parametric form, with the basic thermodynamic variables represented by the particle number density, and by the specific entropy, respectively. The first variation of the matter energy-momentum tensor turns out to be independent on the matter Lagrangian, and can be expressed in terms of the pressure, the energy-momentum tensor itself, and the matter fluid four-velocity. We apply the obtained results for the case of the $f(R,T)$ gravity theory, where $R$ is the Ricci scalar, and $T$ is the trace of the matter energy-momentum tensor, which thus becomes a unique theory, also independent on the choice of the matter Lagrangian. A simple cosmological model, in which the Hilbert-Einstein Lagrangian is generalized through the addition of a term proportional to $T^n$ is considered in detail, and it is shown that it gives a very good description of the observational values of the Hubble parameter up to a redshift of $z\approx 2.5$.

gr-qc↗

arXiv2024

Semi-Symmetric Metric Gravity: A Brief Overview

We present a review of the Semi-Symmetric Metric Gravity (SSMG) theory, representing a geometric extension of standard general relativity, based on a connection introduced by Friedmann and Schouten in 1924. The semi-symmetric connection is a connection that generalizes the Levi-Civita one, by allowing for the presence of a simple form of the torsion, described in terms of a torsion vector. The Einstein field equations are postulated to have the same form as in standard general relativity, thus relating the Einstein tensor constructed with the help of the semi-symmetric connection, with the energy-momentum tensor. The inclusion of the torsion contributions in the field equations has intriguing cosmological implications, particularly during the late-time evolution of the Universe. Presumably, these effects also dominate under high-energy conditions, and thus SSMG could potentially address unresolved issues in General Relativity and cosmology, such as the initial singularity, inflation, or the $^7$Li problem of the Big-Bang Nucleosynthesis. The explicit presence of torsion in the field equations leads to the non-conservation of the energy-momentum tensor, which can be interpreted within the irreversible thermodynamics of open systems, as describing particle creation processes. We also review in detail the cosmological applications of the theory, and investigate the statistical tests for several models, by constraining the model parameters via comparison with several observational datasets.

gr-qc↗