arXiv subjects

Y. Myrzakulov

Publications and source records attributed to Y. Myrzakulov.

4 recordsLinked to original sources

arXiv2026

Event Horizon Telescope Observational Constraints on Dymnikova-Type Non-Singular Black Holes in Higher Dimensions

Black holes are among the most compelling predictions of general relativity (GR) and are now strongly supported by observations from gravitational-wave detectors and the Event Horizon Telescope (EHT). While standard black hole solutions suffer from central singularities, regular black holes avoid this issue by introducing a nonsingular core. In this work, we extend the Dymnikova regular black hole to higher dimensions using a smooth matter distribution. The resulting spacetime features a de Sitter-like core and two horizons. We analyze photon motion and show that circular photon orbits remain unstable, giving rise to a well-defined black hole shadow. Our results indicate that the shadow size grows with the black hole scale but decreases slightly as the number of dimensions increases. We also investigate thermodynamic properties, including Hawking temperature and energy emission, and find a strong dependence on dimensionality. Finally, we compare our model with EHT observations to place constraints on the parameters and highlight potential observational signatures of higher-dimensional regular black holes.

gr-qc↗

arXiv2025

Modified cosmology in $f(Q, L_m)$ gravity

In this letter, we investigate cosmology within the framework of modified $f(Q, L_m)$ gravity using the non-linear model $f(Q, L_m) = -Q + αL_m^n + β$, where $α$, $β$, and $n$ are free parameters. The modified Friedmann equations are derived for a matter-dominated universe, and an analytical solution is obtained. Using Hubble, Pantheon+, and joint datasets, we constrain the model parameters and examine their implications. The results indicate that the model accommodates varying $H_0$ values, contributing to the Hubble tension, while $n \neq 1$ suggests deviations from general relativity (GR). The deceleration parameter confirms a transition to acceleration at $z_t \approx 0.6 - 0.8$, with present values supporting cosmic acceleration. This model offers a viable alternative to GR-based cosmology.

astro-ph.CO↗

arXiv2025

Energy conditions in $f(Q, L_m)$ gravity

We are experiencing a golden age of experimental cosmology, with exact and accurate observations being used to constrain various gravitational theories like never before. Alongside these advancements, energy conditions play a crucial theoretical role in evaluating and refining new proposals in gravitational physics. We investigate the energy conditions (WEC, NEC, DEC, and SEC) for two $f(Q, L_m)$ gravity models using the FLRW metric in a flat geometry. Model 1, $f(Q, L_m) = -αQ + 2L_m + β$, features linear parameter dependence, satisfying most energy conditions while selectively violating the SEC to explain cosmic acceleration. The EoS parameter transitions between quintessence, a cosmological constant, and phantom energy, depending on $α$ and $β$. Model 2, $f(Q, L_m) = -αQ + λ(2L_m)^2 + β$, introduces nonlinearities, ensuring stronger SEC violations and capturing complex dynamics like dark energy transitions. While Model 1 excels in simplicity, Model 2's robustness makes it ideal for accelerated expansion scenarios, highlighting the potential of $f(Q, L_m)$ gravity in explaining cosmic phenomena.

astro-ph.CO↗

arXiv2025

Constraining $f(Q, L_m)$ gravity with bulk viscosity

We investigate the influence of bulk viscosity on late-time cosmic acceleration within an extended $f(Q, L_m)$ gravity framework, where the non-metricity $Q$ is non-minimally coupled with the matter Lagrangian $L_m$. Analyzing the function $f(Q, L_m) = αQ + βL_m$, we derive exact solutions under non-relativistic matter domination. Using observational datasets ($H(z)$, Pantheon supernovae, and their combination), we constrain the model parameters $H_0$, $α$, $β$, and $ζ$. The deceleration parameter transitions from positive to negative values around redshifts $z_t \approx 0.80$ to $0.99 $, indicating current accelerated expansion. Moreover, the effective equation of state parameter, $ω_{eff}$, resembles quintessence dark energy ($-1 < ω_{eff} < -\frac{1}{3}$), with corresponding values from respective datasets. Finally, we use the $Om(z)$ diagnostic, which confirms that our model demonstrates quintessence-like behavior. Our findings underscore the significant role of bulk viscosity in understanding accelerated expansion in the universe within alternative gravity theories.

astro-ph.CO↗