arXiv subjects

Sergey G. Rubin

Publications and source records attributed to Sergey G. Rubin.

At least 19 recordsLinked to original sources

arXiv2026

Multidimensional arrow of time

This paper investigates the influence of extra dimensions on the nature of the arrow of time. We demonstrate that the observed arrow of time can be explained by the monotonic growth of the multidimensional manifold's volume. Unlike traditional cosmological approaches based on the entropy of matter or radiation, our model identifies the primary temporal direction with the Bekenstein-Hawking-Wald entropy of the geometric background. By establishing a formal relation between the statistical weight of the multidimensional manifold and the multiplicity of causally disconnected regions, we reveal that time's directionality is driven by dominant entropy production in the higher-dimensional bulk. A key consequence of this approach is that the arrow of time remains a persistent feature for a 4D observer even in the vacuum limit. This global geometric evolution suppresses local statistical fluctuations and ensures a robust and stable entropy flow throughout the manifold.

gr-qc↗

arXiv2026

Formation of Asymmetrical Two-Brane Structure and its Possible Manifestation

In this paper, we consider the class of extra-dimensional models with two branes and show that each field of the Standard Model must be localized on both neighboring branes, whose asymmetry is of great importance. The discussion is conducted in the framework of a previously developed model. Here we show that the Higgs vacuum average is brane-dependent. As the result, fermion masses on the two branes are also different. The second brane (brane-2) lacks observers, eliminating the need for fine-tuning; consequently the particle masses remains of the order of the initial energy scale of the universe formation. Such superheavy charged leptons may serve as a small component of dark matter. Additionally, we show that inter-brane interactions mediated by photons enable massive fermions in brane-2 to act as sources of ultra-high-energy particles. The gauge fields are uniformly distributed in the bulk, ensuring charge universality.

hep-th↗

arXiv2025

Six-dimensional cosmological models with conformal extensions

We consider the background cosmological solutions in the $6D$ (six-dimensional) model with one time and five space coordinates. The theory of our interest has the action composed by the Einstein term, cosmological constant, and two conformal terms constructed from the third powers of the Weyl tensor. It is shown how the highest derivative terms in the equations of motion can be isolated that opens the way for their numerical integration. There are flat anisotropic solutions which make one of the flat isotropic subspaces to be static. Depending on the value of bare cosmological constant, either two-dimensional or three-dimensional subspace can be static. In particular, there is a physically favorable solution with three ``large'' space coordinates and two extra inner dimensions stabilized. This solution is stable for a wide range of coupling constants, but this requires a special value of the bare cosmological constant.

gr-qc↗

arXiv2025

Formation and evolution of a 2-brane structure in multidimensional $f(R)$ gravity

It has been previously shown that multidimensional $f(R)$ gravity {can lead} to a two-brane structure. In this paper, we analyze such a model with a spatially flat 4D de Sitter (dS) cosmology {whose Hubble parameter $H$ determines the universal energy scale}. We show that the two-brane metric is nucleated at the highest energies. The distance between the branes grows gradually as the energy decreases, tending to a finite value at zero energy density. It is stated that the physical parameters such as the 4D Planck mass, the Higgs vacuum expectation value, and vacuum energy density vary with the evolving universal energy scale, even on the classical level. We also show that the Higgs vacuum expectation value is different on different branes.

gr-qc↗

arXiv2025

Spontaneous branes formation

This paper presents a study of brane formation in six-dimensional space. There is no a priori assumption of the brane(s) existence. However, the analysis of the generalized Einstein equations reveals that there are a set of metrics describing two static branes even in the absence of matter fields. The trapping of massive particles on branes is a consequence of the metric structure, which prevents these particles from moving between branes. It is shown that the communication between charged particles located on different branes provides by photons. Such positron-electron annihilation could be experimentaly study at the LHC collider. The Higgs field is distributed between the branes in such a way that it can serve as a Higgs portal connecting two worlds located on different branes. The values of the 4D physical parameters depend on the extra metric structure near the branes. A particular metric of the extra space was found to provide the observed value of the Higgs vacuum average. We also found a non-trivial effect of decompactification of the extra space when the Hubble parameter is varied.

gr-qc↗

arXiv2024

Primordial Black Holes from Spatially Varying Cosmological Constant Induced by Field Fluctuations in Extra Dimensions

The origin and evolution of supermassive black holes (SMBHs) in our universe have sparked controversy. In this study, we explore the hypothesis that some of these black holes may have seeded from the direct collapse of dark energy domains with density significantly higher than the surrounding regions. The mechanism of the origin of such domains relies on the inflationary evolution of a scalar field acting in D dimensions, which is associated with the cosmological constant in our four-dimensional spacetime manifold. Inner space quantum fluctuations of the field during inflation are responsible for the spatial variations of the dark energy density in our space. This finding holds particular significance, especially considering recent evidence from pulsar timing array observations, which supports the existence of a stochastic gravitational wave background consisting of SMBH mergers.

astro-ph.CO↗

arXiv2024

Can a particle moves zigzag in time?

Amplitudes of quantum transitions containing time zigzags are considered. The discussion is carried out in the framework of the Minkowski metric and standard quantum mechanics without adding new postulates. It is shown that the wave function is singular at the instant of the time zigzag. Nevertheless, we argue that time zigzags are not suppressed at the quantum level, but their contribution to the amplitude is zero. The result is valid for a single particle and a non-interacting scalar field.

quant-ph↗

arXiv2023

Multi-scale hierarchy from multidimensional gravity

We discuss the way of solving the hierarchy problem. We show that starting at the Planck scale, the three energy scales -- inflationary, electroweak and the cosmological ones can be restored. The formation of small parameters is proposed that leads to a successful solution of the problem. The tools involved in the process are $f(R)$ gravity and inhomogeneous extra dimensions. Slow rolling of a space domain from the Planck scale down to the inflationary one gives rise to three consequences: an infinite set of causally disconnected domains (pocket universes) are nucleated; quantum fluctuations in each domain produce a variety of different fields and an extra-dimensional metric distribution; these distributions are stabilized at a sufficiently low energy scale.

gr-qc↗

arXiv2023

Flexible extra dimensions

This paper discusses the origin of the small parameters with the aim of explaining the Hierarchy problem. The flexible extra dimensions are an essential tool in the process by which physical parameters are formed. The evolution of a multidimensional metric starts at the Planck scale and is completed with the static extra-dimensional metric and the 4-dim de Sitter space at high energies, where the exponential production of causally disconnected universes begins. Quantum fluctuations independently distort the metric within these universes, causing inflationary processes within them. Some of these universes tend asymptotically towards states characterised by small Hubble parameters. The effective parameter reduction applied to the Higgs sector of the Standard Model is explained by the presence of small-amplitude distributions of a scalar field in a fraction of these universes.

gr-qc↗

arXiv2022

Self-tuning inflation

We develop an inflationary model without small parameters on the basis of multidimensional $f(R)$ gravity with a minimally coupled scalar field. The model is described by two stages of space expansion. The first one begins at energy scales about the D-dimensional Planck mass and ends with the de Sitter metric of our space and the maximally symmetric extra dimensions. In the following, the quantum fluctuations produce a wide set of inhomogeneous extra metrics in causally disconnected regions quickly generated in the de Sitter space. We find a specific extra space metric that leads to the effective Starobinsky model that fits the observational data.

gr-qc↗

arXiv2022

Compact extra dimensions as the source of primordial black holes

We discuss the model of the primordial black holes formation at the reheating stage. These small massive black holes appear due to specific properties of the compact extra dimensions. The latter gives rise the low energy model containing the effective scalar field potential capable for the domain walls production. Formed during inflation, these walls are quite dense so they collapse soon after inflation ends. The discussion is performed within the scope of multidimensional $f(R)$-gravity.

gr-qc↗

arXiv2021

Distortion of extra dimensions in the inflationary Multiverse

We discuss the effect of the quantum fluctuations at high energies on the final shape of compact extra dimensions. The quantum fluctuations produce a wide range of the initial extra metrics in causally disconnected regions (pocket universes) of the Multiverse during the inflationary stage. This set of initial extra metrics evolves to a set of inhomogeneous metrics at the present time. The low energy physics appears to be different in different pocket universes. The numerical estimate of the probability of finding a specific metric is based on the model of the compact 2-dimensional extra space.

gr-qc↗

arXiv2021

Cosmological baryon/lepton asymmetry in terms of Kaluza-Klein extra dimensions

In this article, we discuss the mechanism for generating the lepton/baryon number and its subsequent conservation based on extradimensional evolution. The internal angular momentum of extra space is related to the lepton/baryon charge. Extra space metric are assumed to be initially asymmetric. Symmetries appear during inflation due to an increase in entropy. Using the multidimensional field toy model, we show that internal angular momentum can accumulate in fermions, which could explain the lepton/baryon asymmetry of the Universe.

hep-ph↗

arXiv2021

On mass spectra of primordial black holes

Evidences for the primordial black holes (PBH) presence in the early Universe renew permanently. New limits on their mass spectrum challenge existing models of PBH formation. One of the known model is based on the closed walls collapse after the inflationary epoch. Its intrinsic feature is multiple production of small mass PBH which might contradict observations in the nearest future. We show that the mechanism of walls collapse can be applied to produce substantially different PBH mass spectra if one takes into account the classical motion of scalar fields together with their quantum fluctuations at the inflationary stage.

astro-ph.CO↗

arXiv2021

Local regions with expanding extra dimensions

We study possible spatial domains containing expanding extra dimensions. We show that they are predicted in the framework of $f(R)$ gravity and could appear due to quantum fluctuations during inflation. Their interior is characterized by the multidimensional curvature ultimately tending to zero and a slowly growing size of the extra dimensions.

gr-qc↗

arXiv2021

Looking at the NANOGrav Signal Through the Anthropic Window of Axion-Like Particles

We explore the inflationary dynamics leading to formation of closed domain walls in course of evolution of an axion like particle (ALP) field whose Peccei-Quinn-like phase transition occurred well before inflationary epoch. Evolving after inflation, the domain walls may leave their imprint in stochastic gravitational waves background, in the frequency range accessible for the pulsar timing array measurements. We derive the characteristic strain power spectrum produced by the distribution of the closed domain walls and relate it with the recently reported NANOGrav signal excess. We found that the slope of the frequency dependence of the characteristic strain spectrum generated by the domain walls is very well centered inside the range of the slopes in the signal reported by the NANOGrav. Analyzing the inflationary dynamics of the ALP field, in consistency with the isocurvature constraint, we revealed those combinations of the parameters where the signal from the inflationary induced ALPs domain walls could saturate the amplitude of the NANOGrav excess. The evolution of big enough closed domain walls may incur in formation of wormholes with the walls escaping into baby universes. We studied the conditions, when closed walls escaped into baby universes could leave a detectable imprint in the stochastic gravitational waves background.

hep-ph↗

arXiv2021

Sub-Planckian scale and limits for $f(R)$ models

We study the Universe evolution starting from the sub-Planckian scale to present times. The requirement for an exponential expansion of the space with the observed metric as a final stage leads to significant restrictions on the parameter values of a $f(R)$-function. An initial metric of the Universe is supposed to be maximally symmetric with the positive curvature.

gr-qc↗

arXiv2020

Gravity with Higher Derivatives in D-Dimensions

The aim of this review is to discuss the ways to obtain results based on gravity with higher derivatives in D-dimensional world. We considered the following ways: (1) reduction to scalar tensor gravity, (2) direct solution of the equations of motion, (3) derivation of approximate equations in the presence of a small parameter in the system, and (4) the method of test functions. Some applications are presented to illustrate each method. The unification of two necessary elements of a future theory is also kept in mind - the extra dimensions and the extended form of the gravity.

gr-qc↗