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K. Myrzakulov

Publications and source records attributed to K. Myrzakulov.

16 recordsLinked to original sources
arXiv2026

Extended thermodynamics and $P-v$ Criticality of Kalb-Ramond black hole coupled with nonlinear electrodynamics

We present an exact black hole solution in anti-de Sitter (AdS) spacetime with a Kalb-Ramond field coupled to nonlinear electrodynamics (NLED), characterized by mass, magnetic monopole charge, and Lorentz-violating parameters. The geometry admits two horizons (inner and outer) that coalesce into a degenerate horizon at a critical monopole charge. Beyond this critical point, no black hole solutions exist. In the limit of vanishing Lorentz-violating parameters, the solution reduces to the modified Kalb-Ramond and Bardeen black holes, while suitable parameter choices reproduce the Reissner-Nordström-AdS and Schwarzschild-AdS geometries. We analyze the thermodynamics of the solution by computing the Hawking temperature, entropy, specific heat, and Gibbs free energy. The NLED source introduces nontrivial modifications: the Hawking temperature displays nonmonotonic behavior with possible local extrema, the entropy deviates from the standard area law, and the specific heat may assume negative values, signaling thermodynamic instabilities. The Gibbs free energy exhibits swallow-tail structures, indicative of first-order phase transitions. Furthermore, we derive the first law of black hole thermodynamics in the extended phase space, together with the Smarr relation, and confirm their validity for the Kalb-Ramond black holes with NLED sources. Our findings highlight the rich thermodynamic structure induced by Lorentz-violating effects and nonlinear electrodynamics in AdS black hole backgrounds.

gr-qc↗
arXiv2025

Quantum corrections to Dymnikova-Schwinger black holes in Einstein-Gauss-Bonnet gravity

This work investigates black holes within a modified framework of gravity that incorporates quantum-inspired corrections and a fundamental minimal length scale. By integrating Einstein-Gauss-Bonnet gravity with a specially tailored matter source that models quantum particle creation, we derive novel, non-singular black hole solutions. These black holes exhibit rich horizon structures and, notably, do not undergo complete evaporation -- instead, they stabilize into permanent remnants. In addition to analyzing the thermodynamic implications of quantum corrections to Dymnikova-Schwinger black holes, we examine their quasinormal mode spectra using the WKB approximation, alongside their associated energy emission rates. Our findings provide compelling new perspectives on how quantum effects may address foundational issues such as the black hole information loss paradox.

gr-qc↗
arXiv2025

Dehnen-type dark matter wormholes in the $f(\mathcal{R},\mathcal{L}_m,\mathcal{T})$ action

We are exploring the possibility of traversable wormholes existing in a more realistic context. Specifically, we are looking at scenarios that don't rely on exotic factors, like having a mass shell at the throat or allowing particles and antiparticles to coexist without annihilation. To do this, we are constructing wormholes with double power-law density distributions, drawing inspiration from the Dehnen-type dark matter halo in the framework of generalized geometry-matter coupling gravity. Our investigation carefully considers the challenges of traversability and stability, as well as the roles of exotic matter, the exoticity parameter, and the anisotropy parameter. We have discovered solutions that describe asymmetric, asymptotically flat traversable wormholes, supported by a smooth metric and double power-law density distributions. These solutions successfully avoid the problems, giving us hope that such wormholes could actually exist in nature.

gr-qc↗
arXiv2025

Possible wormholes in generalized geometry-matter coupling gravity induced by the Dekel-Zhao dark matter profile

In the late 1980s, Morris and Thorne led in theoretical physics by creating solutions to wormholes and formulating the crucial requirements for safe traversability of wormholes. They found that exotic matter must meet the requirement $P_r + ρ< 0$, where $P_r$ is radial pressure and $ρ$ is energy density. This is a rudimentary grasp of our understanding of general relativity. In this paper, we continue their excellent work by looking at how to build traversable wormhole solutions in an extended theory of gravity. We adopt a process of linearly modifying the matter Lagrangian and the energy-momentum tensor with some coupling strengths $λ$ and $χ$. This may be considered as a special case of linear $f(R, T)$ gravity with matter coupling variability or as an additively separable simple $f(R, L_m, T)$ model. We undertake a detailed analysis of static wormhole solutions with a constant redshift function. This allows us to present our results as a first-order approximation in the $f(R, L_m, T)$ scenario. We derive the wormhole shape function from the Dekel-Zhao dark matter distribution in such a way that our solutions satisfy the needed conditions for traversability as well as the requirement of exotic matter. This is particularly exciting as it shows that wormholes in $f(R, L_m, T)$ gravity can sustain both exotic as well as ordinary matter. To ensure that the shape function meets the requirement of flaring-out and is asymptotically flat, we place some constraints on the couplings. We also examine the gravitational lensing effects, which exhibit a repulsive gravitational force that appears in our extended gravity for positive couplings.

gr-qc↗
arXiv2024

Constraints on bulk viscosity in $f(Q,T)$ gravity from H(z)/Pantheon+ data

In this study, we investigate the role of bulk viscosity in $f(Q,T)$ gravity in explaining late-time cosmic acceleration. This model, an extension of symmetric teleparallel gravity, introduces viscosity into cosmic matter dynamics for a more realistic representation. Specifically, we consider the linear form of $f (Q, T) =αQ + βT$, where $α$ and $β$ are free model parameters. To assess the model, we derive its exact solution and use Hubble parameter $H(z)$ data and Pantheon + SNe Ia data for parameter estimation. We employ the $χ^2$ minimization technique alongside the MCMC random sampling method to determine the best-fit parameters. Then, we analyze the behavior of key cosmological parameters, including the deceleration parameter, bulk viscous matter-dominated universe density, effective pressure, and the effective EoS parameter, accounting for the viscous type fluid. We observe a transition in the deceleration parameter from a positive (decelerating) to a negative (accelerating) phase at transition redshift $z_t$. The matter density shows the expected positive behavior, while the pressure, influenced by viscosity, exhibits negative behavior, indicative of accelerating expansion. Furthermore, we investigate the energy conditions and find that while the NEC and DEC meet positivity criteria, the SEC is violated in the present and future epochs. The $Om(z)$ diagnostic suggests that our model aligns with quintessence behavior. Finally, our $f(Q,T)$ cosmological model, incorporating bulk viscosity effects, provides a compelling explanation for late-time cosmic behavior, consistent with observational data.

astro-ph.CO↗
arXiv2024

Metric-affine Myrzakulov gravity theories with Gauss-Bonnet and boundary term scalars

In this paper, we consider some metric-affine Myrzakulov gravity (MG) theories with Gauss-Bonnet scalars. Also we consider the MG theories with the boundary term scalars. Note that these MG theories with the Gauss-Bonnet and boundary term scalars were proposed in [arXiv:1205.5266]. Some examples of Metric-Affine Gravity (MAG) theories are reviewed in the context of the $F(R,T,Q,{\cal T}, {\cal D})$ type models. Then the generalized MAG theory with the curvature, torsion and nonmetricity (the so-called MG-VIII) was studied. For the FRW spacetime case, in particular, the Lagrangian, Hamilatonian and gravitational equations are obtained. The particular case $F(R,T)=αR+βT+μQ+ν{\cal T}$ is investigated in detail. In quantum case, the corresponding Wheeler-DeWitt equation is obtained. Finally, some gravity theories with the curvature, torsion and nonmetricity are presented.

gr-qc↗
arXiv2022

Reconstruction of the quintessence dark energy potential from a Gaussian process

The quintessence dark energy potential is reconstructed in a model-independent way. Reconstruction relies on a Gaussian process and on available expansion-rate data. Specifically, 40-point values of $H(z)$ are used, consisting of a 30-point sample deduced from a differential age method and an additional 10-point sample obtained from the radial BAO method. Results are obtained for two kernel functions and for three different values of $H_{0}$. They shed light on the $H_{0}$ tension problem for a universe described with quintessence dark energy. They are also a clear indication that the tension has to do with the physical understanding of the issue, rather than being just a numerical problem with statistics. Moreover, the model-independent reconstruction of the potential here obtained can serve as a reference to constraint available models and it can be also used as a reference frame to construct new ones. Various possibilities, including $V(ϕ) \sim e^{-λϕ}$, are compared with the reconstructions here obtained, which is notably the first truly model independent reconstruction of the quintessence dark energy potential. This allows to select new models that can be interesting for cosmology. The method can be extended to reconstruct the potential of related dark energy models, to be considered in future work.

gr-qc↗
arXiv2021

Viscous coupled fluids in terms of a log-corrected equation of state

We consider a class of cosmological fluids that possess properties analogous to those of crystalline solids undergoing isotropic deformations. Our research is based on a modified log-corrected power-law equation of state in the presence of a bulk viscosity. This formalism represents a class of so-called logotropic fluids, and allows explaining an accelerating late-time universe. In order to obtain a more detailed picture of its evolution, we add in our model a coupling of the log-corrected power-law fluid to dark matter, and study various interacting forms between them. We solve the system of equations for a modified log-power-law fluid coupled to dark matter, and obtain expressions for the log-corrected power-law energy density, and the energy density for dark matter. A comparative analysis is made with the model of a nonviscous log-corrected power-law fluid without interaction with dark matter.

gr-qc↗
arXiv2017

Cosmological parametrizations and their scalar field descendents

We reconstruct the field potentials in case of (non)phantom fields for different models resulting from parametrization of q(t), a(t) or H(t). In addition we carry out similar procedure for tachyonic field. We also discuss specific form of parametrization for reconstruction of scalar field potential.

gr-qc↗
arXiv2014

FRW cosmology of the generalized model of LQG

In this paper, we study the main cosmological properties of the classical Friedmann equations in the case of homogeneous and isotropic Friedmann-Robertson-Walker Universe and we also generalized the expression of the Friedmann equation in the case of Loop Quantum Cosmology (LQC). Considering the $M_{35}$-model, we found the solutions of the equations considered for two particular cases, i.e. $Q=0$ (i.e., the de Sitter solution) and $Q>0$. Moreover, we considered and studied two exact cosmological solutions of the $M_{35}$-model, in particular the power-law and the exponential ones. Futhermore, we also considered a third more complicated case and we derived the solution for an arbitrary function of the time $f\left(t\right)$. A scalar field description of the model is presented by constructing its self-interacting potential.

gr-qc↗
arXiv2010

Classical gauge field as a dark matter

The model of dark matter is presented where the dark matter is a \emph{classical} gauge field. A spherical symmetric solution of Yang-Mills equation is obtained. The asymptotic behavior of the gauge fields and matter density is investigated. It is shown that the distribution of the matter density allows us interpret it as the dark matter. The fitting of a typical rotational curve with the rotational curve created by the spherical solution of SU(3) Yang-Mills equation is made.

astro-ph.CO↗
arXiv2009

Decelaration/acceleration phases with the Higgs field

It is shown that the Einstein gravity + Higgs scalar field have cosmological regular solutions with deceleration/acceleration phases and with bouncing off from a singularity. The behavior of the solution near to a flex point is in detail considered.

gr-qc↗
arXiv2006

Boson stars from a gauge condensate

The boson star filled with two interacting scalar fields is investigated. The scalar fields can be considered as a gauge condensate formed by SU(3) gauge field quantized in a non-perturbative manner. The corresponding solution is regular everywhere, has a finite energy and can be considered as a quantum SU(3) version of the Bartnik - McKinnon particle-like solution.

gr-qc↗
arXiv2006

Cosmic string with two interacting scalar fields

The model of cosmic string formed from two gravitating and interacting scalar fields is considered. It is shown that the regular solutions exist at special choice of the model's parameters only.

gr-qc↗