arXiv subjects

Oleg Zenin

Publications and source records attributed to Oleg Zenin.

5 recordsLinked to original sources

arXiv2026

Non-minimal Effective Scalar-Tensor Gravity in the Early Universe

We study the consistency of several early-Universe scenarios within a framework of non-minimal effective sca\-lar--ten\-sor gravity. We show that bounce, inflation, and genesis stages are supported within the aforementioned theory. Consequently, this framework can serve as a viable model of the early Universe, where accelerated expansion is driven by the theory's own intrinsic degrees of freedom. Notably, the theory also provides two different values of the Hubble parameter, potentially explaining the different values of the Hubble constant measured from galaxy clusters and relic radiation, respectively.

gr-qc↗

arXiv2025

Constraints of extended gravity theory in the regime of Universe accelerated extension: turnaround radius

Applying the definition of the turnaround radius and the fact that the best agreement with observational data on extragalactic scales is currently provided by general relativity with the cosmological constant we consider the behaviour of spherically symmetric solutions of the Horndeski and Dvali-Gabadadze-Poratti models on these scales. Therefore, the conditions on the turning radius together with astronomical data for galaxy clusters allow us to place additional constraints on the parameters of extended gravity theories.

gr-qc↗

arXiv2025

Black Hole Shadows Modelling in Extended gravity: Rotation Accounting and coupled effects

Using an improved version of the Newman-Janis algorithm, we obtain metrics of rotating black holes for a set of extended gravity theories that extend general relativity in different ways: the Horndeski model, the bumblebee model, the Gauss-Bonnet scalar gravity, the loop quantum gravity, the conformal gravity, and $f(Q)$ (symmetric teleparallel gravity STEGR). The obtained metrics are used to model black hole shadows. It is shown that for some models the critical values of the angular momentum $a_{crit}$ emerge. The previous conclusion that the extended gravity theory corrects by itself the effects of rotation in both directions is confirmed. This appears to be important for further modelling of shadow profiles taking into account the constantly increasing accuracy of black hole images. Thus, when rotation is taken into account black hole shadow images, as the GW170817 test or the post-Newtonian formalism, can serve as a meaningful way to test and constrain extended theories of gravity.

gr-qc↗

arXiv2024

Extended Gravity and Black Hole Shadows: Rotation Accounting

We obtain black hole rotating solutions for Horndesky theory (specific partial case), bumblebee model and Gauss-Bonnet scalar gravity using the specially improved Newman-Janis algorithm. The shadow profiles for these metrics were calculated. Applying the limitations from the Event Horizon Telescope we find the opportunity to constrain model parameters from considered extended gravity theories. We show that for three considered models two of them (Horndesky theory and Gauss-Bonnet scalar gravity) weaken the effect of rotation and bumblebee model enhances it. This conclusion matches the previously obtained one that extended gravity theories by themselves correct the effect of rotation in both directions.

gr-qc↗

arXiv2024

Non-local gravitational corrections in black hole shadow images

With the help of Newman-Janis method new spinning black hole (BH) solution for a non-local gravity model was obtained. We show how to account the quantum gravitational correction part in BH shadows modelling using spinning BH metrics with a model independent approach. It is confirmed that in the future to follow the increasing of the experimental accuracy and therefore to reproduce new results theoretically one could take into account different field correction terms instead of introducing of new fields and/or curvature expansions.

gr-qc↗