arXiv subjects

G. S. Nurbakova

Publications and source records attributed to G. S. Nurbakova.

4 recordsLinked to original sources

arXiv2026

Quasinormal modes in the field of a dyon-like dilatonic black hole corresponding to $A_1 + A_1$ Toda chain

We explore the quasinormal modes of a massless test scalar field in the gravitational background of a non-extremal dilatonic dyonic black hole. The dyon-like black hole solution is considered within a four-dimensional gravitational model that includes two scalar fields and two 2-forms. It is governed by two dilatonic coupling vectors $\vecλ_s$ (with $s=1,2$) that satisfy $\vecλ_1 = \vecλ_2 = \vecλ$ and $\vecλ^2 = 1/2$. We derive and examine the quasinormal modes of a massless scalar test field in the eikonal limit. These modes are governed by the solution parameters $μ> 0$, $P_1 > 0$, and $P_2 > 0$. In the two limiting scenarios -- namely $P_1 = P_2 = 0$ and $P_1 = P_2 = P > 0$ -- our results reduce exactly to the known (eikonal) quasinormal spectra for the Schwarzschild and Reissner-Nordström black holes, respectively. Numerical higher-order WKB analysis of quasinormal frequencies for two lower levels (for various values of parameters) is also presented.

gr-qc↗

arXiv2026

Photon Sphere for a Dilatonic Dyonic Black Hole in a Model with an Abelian Gauge Field and a Scalar Field

Dilatonic dyon black hole solution with gravitational radius $2 μ$ and two charges $Q_1$ and $Q_2$ (electric and magnetic ones) in the gravitational $4d$ model with one scalar field and one 2-form is considered. Dilatonic coupling constant $λ$ obeys $λ^2 = \frac{1}{2}$. The circular orbits for null geodesics are explored. The 3rd order polynomial master equation for radius $R_0$ of photon sphere is studied. It has only one solution which obeys $R_0 > 2 μ$. The circular null geodesics are shown to be unstable. The black hole shadow is studied and relations for shadow angle and critical impact parameter are obtained.

gr-qc↗

arXiv2026

On gravitating dyonic configurations in nonlinear electrodynamics

We consider static, spherically symmetric configurations of nonlinear electromagnetic fields with Lagrangians $L(f)$, where $f = F_{μν} F^{μν}$, in general relativity (GR) and other metric theories of gravity. The corresponding exact solutions are well known in the framework of GR in cases where only an electric charge ($q_e$) or a magnetic charge ($q_m$) are present, but only a few solutions in particular examples of $L(f)$ are known for dyonic systems with both nonzero $q_e$ and $q_m$. We study the properties of such systems in the special case of equal electric and magnetic charges and, assuming a correct Maxwell limit of $L(f)$, show that there always exists such a configuration of the electromagnetic field that the invariant $f$ is zero in the whole space. It leads to the existence of the corresponding families of solutions both in GR in the presence of other sources of gravity (like fluids or scalar fields) and in a wide range of extended theories of gravity (e.g., scalar-tensor and $F(R)$ gravity), in which the nonlinear electromagnetic field behaves in an especially simple manner.

gr-qc↗

arXiv2025

Photon spheres near black holes in a model with anisotropic fluid

The semi-review paper studies the null geodesics which appear for black hole solutions in the gravitational $4d$ model with anisotropic fluid. The equations of state for the fluid and solutions itselves depend upon integer parameter $q = 1, 2, ...$: $p_r = -ρc^2 (2q-1)^{-1}, \quad p_t = - p_r$, where $ρ$ is the mass density, $c$ is speed of light, $p_r$ and $p_t$ are pressures in radial and transverse to radial directions, respectively. The circular null geodesics are explored and the master equation for radius $r_*$ of photon sphere is outlined as well as the proposition on existence and uniqueness of the solution to master equation obeying $r_* > r_h$, where $r_h$ is horizon radius. The relations for spectrum of quasinormal modes for a test massless scalar field in the eikonal approximation are overviewed and compared with cyclic frequencies of circular null geodesics. The shadow angles are explored.

gr-qc↗