arXiv subjects

R. Myrzakulov

Publications and source records attributed to R. Myrzakulov.

At least 19 recordsLinked to original sources

arXiv2026

Integrable Zhaidary equations: reductions and gauge equivalence

The present work addresses the study and characterization of the integrability of some generalized spin systems (ISS) in 1+1 dimensions. Lax representations for these ISS are successfully obtained. The gauge equivalent counterparts of these integrable ISS are presented. Finally, we consider Zhanbota transcendents and some integrable Zhanbota equations. In particular, the gauge equivalence between some Zhanbota equations and the six Painleve equations is established.

nlin.SI↗

arXiv2025

Integrability, geometry and wave solutions of some Kairat equations

In this paper, we study some Kairat equations. The relation between the motion of curves and Kairat equations is established. The geometrical equivalence between the Kairat-I equation and the Kairat-II equation is proved. We also proves that these equations is gauge equivalent to each other. Three types traveling wave solutions of the Kairat-II equation as well as its some integrals of motion are found. The techniques used in this paper can be adopted to study other integrable spin systems and nonlinear models. In particular, using these methods we study some Zhanbota equations.

nlin.SI↗

arXiv2025

Integrable Kuralay equations: geometry, solutions and generalizations

In this paper, we study the Kuralay equations, namely, the Kuralay-I equation (K-IE) and the Kuralay-II equation (K-IIE). The integrable motion of space curves induced by these equations is investigated. The gauge equivalence between these two equations is established. With the help of the Hirota bilinear method, the simplest soliton solutions are also presented. The nonlocal and dispersionless versions of the K-IE and K-IIE are considered.

nlin.SI↗

arXiv2024

FLRW Cosmology in Metric-Affine $F(R,Q)$ Gravity

We investigate some FLRW cosmological models in the context of Metric-Affine $F(R,Q)$ gravity, as proposed in [arXiv:1205.52666]. Here, $R$ and $Q$ are the curvature and nonmetricity scalars using non-special connections, respectively. We get the modified field equations using a flat Friedmann-Lemaître-Robertson-Walker (FLRW) metric. We then find a connection between the Hubble constant $H_{0}$, the density parameter $Ω_{m0}$, and the other model parameters in two different situations involving scalars $u$ and $w$. Next, we used new observational datasets, such as the cosmic chronometer (CC) Hubble datasets and the Pantheon SNe Ia datasets, to determine the optimal model parameter values through MCMC analysis. Using these best-fit values of model parameters, we have discussed the results and behavior of the derived models. We have also discussed the AIC and BIC criteria for the derived models in the context of $Λ$CDM. We have found that the geometrical sector dark equation of state parameter $ω_{de}$ behaves just like a dark energy candidate. We have found that both models are transit phase models and Model-I approaches to the Lambda CDM model in the late-time universe and Model-II approaches to quintessence scenarios.

gr-qc↗

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↗

arXiv2024

On the dilation current in metric-affine gravity

We review $F(R,\mathcal{D})$ gravity in the metric-affine framework, where $\mathcal{D}$ is the divergence of the dilation current appearing in the hypermomentum tensor. We assume only linear couplings between the general affine connection and the matter fields (minimal coupling) and break projective invariance to preserve a nonvanishing dilation current. For $F(R,\mathcal{D})$ linear in $\mathcal{D}$ the dilation current dependence in the function $F(R,\mathcal{D})$ does not contribute to the field equations of the theory. We show that, on the other hand, in more complicated cases (e.g., considering the function $F(R,\mathcal{D})=R+α\mathcal{D}^2$), the $\mathcal{D}$ contribution to the metric field equations is nontrivial and can affect the cosmology of the theory.

hep-th↗

arXiv2024

Myrzakulov $F(T,Q)$ gravity: cosmological implications and constraints

In this paper, we investigate some exact cosmological models in Myrzakulov $F(T,Q)$ gravity or the Myrzakulov gravity-III (MG-III) proposed in [arXiv:1205.5266], with observational constraints. The MG-III gravity is some kind of unification of two known gravity theories, namely, the $F(T)$ gravity and the $F(Q)$ gravity. The field equations of the MG-III theory are obtained by regarding the metric tensor and the general affine connection as independent variables. We then focus on the particular case in which the $F(T,Q)$ function characterizing the aforementioned metric-affine models is linear that is $F(T,Q)=λT+μQ$. We investigate this linear case and consider a Friedmann-Lemaître-Robertson-Walker background to study cosmological aspects and applications. We have obtained three exact solutions of the modified field equations in different cases $T$ and $Q$, in the form of Hubble function $H(t)$ and scale factor $a(t)$ and placed observational constraints on it through the Hubble $H(z)$ datasets on it using the MCMC analysis. We have investigated the deceleration parameter $q(z)$, effective EoS parameters and a comparative study of all three models with $Λ$CDM model has been carried out.

gr-qc↗

arXiv2024

Generic autonomous system approach to interacting dark energy models

We explore an autonomous system analysis of dark energy models with interactions between dark energy and cold dark matter in a general systematic approach to cosmological fluids. We investigate two types of models such as local and non-local ones. In particular, a local form of interaction is directly proportional to only the energy density, while a non-local interaction is directly proportional to the energy density as well as the Hubble parameter. As a consequence, it is explicitly demonstrated that in both cases there exist the stability points in terms of cosmological parameters. This work aims at obtaining acceleration and stability using interaction models without modifying the matter or geometric component of the Universe.

gr-qc↗

arXiv2024

Dynamical system analysis in descending dark energy model

In this paper, we study the dynamical system analysis for a recently proposed decaying dark energy model, namely, Q-SC-CDM. First we investigate the stationary points to find the stable attractor solution under the conditions discussed recently in the literature. In this case, we do not find any stable attractor solution. Therefore, we avoid the parameter space of Q-SC-CDM model discussed in arXiv:2201.07704. Second, we make different choice for the model parameters and re-investigate the stationary points and their stability. Our analysis shows that a simple choice of model parameters allows to capture a stable attractor solution. Moreover, we obtain phase portrait where all trajectories move towards the stable attractor point.

gr-qc↗

arXiv2023

Phase structure of charged AdS black holes surrounded by exotic fluid with modified Chaplygin equation of state

By considering the concept of the modified Chaplygin gas (MCG) as a single fluid model unifying dark energy and dark matter, we construct a static, spherically charged black hole (BH) solution in the framework of General Relativity. The $P-V$ criticality of the charged anti-de Sitter (AdS) BH with a surrounding MCG is explored in the context of the extended phase space, where the negative cosmological constant operates as a thermodynamical pressure. This critical behavior shows that the small/large BH phase transition is analogous to the van der Waals liquid/gas phase transition. Accordingly, along the $P-V$ phase spaces, we derive the BH equations of state and then numerically evaluate the corresponding critical quantities. Similarly, critical exponents are identified, along with outcomes demonstrating the scaling behavior of thermodynamic quantities near criticality into a universal class. The use of \emph{geometrothermodynamic} (GT) tools finally offers a new perspective on discovering the critical phase transition point. At this stage, we apply a class of GT tools, such as Weinhold, Ruppeiner, HPEM, and Quevedo classes I and II. The findings are therefore non-trivial, as each GT class metric captures at least either the physical limitation point or the phase transition critical point. Overall, this paper provides a detailed study of the critical behavior of the charged AdS BH with surrounding MCG.

gr-qc↗

arXiv2023

Nonlocal Reductions of a Generalized Heisenberg Ferromagnet Equation

We study nonlocal reductions of coupled equations in $1+1$ dimensions of the Heisenberg ferromagnet type. The equations under consideration are completely integrable and have a Lax pair related to a linear bundle in pole gauge. We describe the integrable hierarchy of nonlinear equations related to our system in terms of generating operators. We present some special solutions associated with four distinct discrete eigenvalues of the scattering operator. Using Lax pair diagonalization method, we derive recurrence formulas for the conserved densities and find the first two simplest conserved densities.

nlin.SI↗

arXiv2022

Spectrum of Primordial Gravitational Waves in Modified Gravities: A Short Overview

In this work we shall exhaustively study the effects of modified gravity on the energy spectrum of the primordial gravitational waves background. S. Weinberg has also produced significant works related to the primordial gravitational waves with the most important one being the effects of neutrinos on primordial gravitational waves. With this sort review, our main aim is to gather all the necessary information for studying the effects of modified gravity on primordial gravitational waves in a concrete and quantitative way and in a single paper. After reviewing all the necessary techniques for extracting the general relativistic energy spectrum, and how to obtain in a WKB way the modified gravity damping or amplifying factor, we concentrate on specific forms of modified gravity of interest. The most important parameter involved for the calculation of the effects of modified gravity on the energy spectrum is the parameter $a_M$ which we calculate for the cases of $f(R,ϕ)$ gravity, Chern-Simons-corrected $f(R,ϕ)$ gravity, Einstein-Gauss-Bonnet-corrected $f(R,ϕ)$ gravity, and higher derivative extended Einstein-Gauss-Bonnet-corrected $f(R,ϕ)$ gravity. The exact forms of $a_M$ is presented explicitly for the first time in the literature. With regard to Einstein-Gauss-Bonnet-corrected $f(R,ϕ)$ gravity, and higher derivative extended Einstein-Gauss-Bonnet-corrected $f(R,ϕ)$ gravity theories, we focus on the case that the gravitational wave propagating speed is equal to that of light's in vacuum. We provide expressions for $a_M$ expressed in terms of the cosmic time and in terms of the redshift, which can be used directly for the numerical calculation of the effect of modified gravity on the primordial gravitational wave energy spectrum.

gr-qc↗

arXiv2022

Three-partite vertex model and knot invariants

This work is dedicated to the consideration of the construction of a representation of braid group generators from vertex models with $N$-states, which provides a great way to study the knot invariant. An algebraic formula is proposed for the knot invariant when different spins $(N-1)/2$ are located on all components of the knot. The work summarizes procedure outputting braid generator representations from three-partite vertex model. This representation made it possible to study the invariant of a knot with multi-colored links, where the components of the knot have different spins. The formula for the invariant of knot with a multi-colored link is studied from the point of view of the braid generators obtained from the $R$-matrices of three-partite vertex models. The resulting knot invariant $5_2$ corresponds to the Jones polynomial and HOMFLY-PT.

cond-mat.stat-mech↗

arXiv2022

Integrable motion of anisotropic space curves and surfaces induced by the Landau-Lifshitz equation

In this paper, we have studied the geometrical formulation of the Landau-Lifshitz equation (LLE) and established its geometrical equivalent counterpart as some generalized nonlinear Schrödinger equation. When the anisotropy vanishes, from this result follows the well-known results corresponding for the isotropic case, i.e. to the Heisenberg ferromagnet equation and the focusing nonlinear Schrödinger equation. The relations between the LLE and the differential geometry of space curves in the local and nonlocal cases are studied. Using the well-known Sym-Tafel formula, the soliton surfaces induced by the LLE are briefly considered.

nlin.SI↗

arXiv2021

Metric-Affine Myrzakulov Gravity Theories

In this paper we review the Myrzakulov Gravity models (MG-N, with $\mathrm{N = I, II, \ldots, VIII}$) and derive their respective metric-affine generalizations (MAMG-N), discussing also their particular sub-cases. The field equations of the theories are obtained by regarding the metric tensor and the general affine connection as independent variables. We then focus on the case in which the function characterizing the aforementioned metric-affine models is linear and consider a Friedmann-Lemaître-Robertson-Walker background to study cosmological aspects and applications.

gr-qc↗

arXiv2021

Cosmological bouncing scenarios in symmetric teleparallel gravity

Symmetric Teleparallel Gravity is an exceptional theory of gravity that is consistent with the vanishing affine connection. This theory is an alternative and a simpler geometrical formulation of general relativity, where the non-metricity $Q$ drives the gravitational interaction. Our interest lies in exploring the cosmological bouncing scenarios in a flat Friedmann-Limaître-Robertson-Walker (FLRW) spacetime within this framework. We explore bouncing scenarios with two different Lagrangian forms of $f(Q)$ such as a linearly and non-linearly dependence on $Q$. We have successfully examined all the energy conditions and stability analysis for both models to present a matter bounce.

gr-qc↗

arXiv2021

Late time attractors of some varying Chaplygin gas cosmological models

The goal of this paper is to study new cosmological models where the dark energy is a varying Chaplygin gas. This specific dark energy model with non-linear EoS had been often discussed in modern cosmology. Contrary to previous studies, we consider new forms of non-linear non-gravitational interaction between dark matter and assumed dark energy models. We applied the phase space analysis allowing understanding the late time behavior of the models. It allows demonstrating that considered non-gravitational interactions can solve the cosmological coincidence problem. On the other hand, we applied Bayesian Machine Learning technique to learn the constraints on the free parameters. In this way, we gained a better understanding of the models providing a hint which of them can be ruled out. Moreover, the learning based on the simulated expansion rate data shows that the models cannot solve the $H_{0}$ tension problem.

gr-qc↗

arXiv2020

Cosmological Einstein-Maxwell model with $g$-essence

In this paper, we study the model of the late universe with the homogeneous, isotropic and flat Friedmann-Robertson-Walker metric, where the source of the gravitational field is based on the fermion and boson field, with the Maxwell term $F_{μν}F^{μν} $ in four dimensions. The actuation of the Maxwell term for the Einstein gravity makes it possible to find new approaches to solve the problem of the observed accelerated expansion of the universe. Energy conditions have been obtained and studied. These conditions impose very simple and model-independent restrictions on the behaviour of energy density and pressure since they do not require a specific equation of state of matter. To consider the model, the energy conditions NEC, WEC, DEC are realized, and the SEC condition is violated. The boson and fermion fields are responsible for the accelerated regime at early times, but since the total pressure is tending toward zero for large times, a transition to a decelerated regime occurs. Maxwell field is crucial only in the early times.

gr-qc↗