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Artyom V. Yurov

Publications and source records attributed to Artyom V. Yurov.

16 recordsLinked to original sources
arXiv2025

Quantum Cosmology Without Singularities: A New Approach

The article is dedicated to a discussion regarding the role of Barrow's ''Zero Universes'' in quantum cosmology. In particular, we demonstrate that if quantum gravity effects are modeled by the quantum potential method associated with the ''many interacting universes'' (MIU) model, then the mere presence of the universes with a zero scale factor (the ``Zero universes'') produces a veritably remarkable outcome: the classical cosmological singularities of Big Bang, Big Crunch and Big Rip all fail to arise. In other words, those universes that are considered ill-posed at the classical level may turn out to be a necessary and sought-after ingredient in a future internally consistent quantum theory of gravity. Finally, we argue that the MIU quantization method might shed light on a number of other cosmological mysteries; for example, it might account for a decoherence which preceded the eternal inflation, and elucidate how the quantum superposition of vacuum decays occurring at different places might give birth to actual bubble universes there. In addition, the new method might help explain why our universe was born in an extremely low-entropy initial state required to trigger the initial inflation.

gr-qc↗
arXiv2018

The Cosmological Models with Jump Discontinuities

The article is dedicated to one of the most undeservedly overlooked properties of the cosmological models: the behaviour at, near and due to a jump discontinuity. It is most interesting that while the usual considerations of the cosmological dynamics deals heavily in the singularities produced by the discontinuities of the second kind (a.k.a. the essential discontinuities) of one (or more) of the physical parameters, almost no research exists to date that would turn to their natural extension/counterpart: the singularities induced by the discontinuities of the first kind (a.k.a. the jump discontinuities). It is this oversight that this article aims to amend. In fact, it demonstrates that the inclusion of such singularities allows one to produce a number of very interesting scenarios of cosmological evolution. For example, it produces the cosmological models with a finite value of the equation of state parameter $w=p/ρ$ even when both the energy density and the pressure diverge, while at the same time keeping the scale factor finite. Such a dynamics is shown to be possible only when the scale factor experiences a finite jump at some moment of time. Furthermore, if it is the first derivative of the scale factor that experiences a jump, then a whole new and different type of a sudden future singularity appears. Finally, jump discontinuities suffered by either a second or third derivatives of a scale factor lead to cosmological models experiencing a sudden dephantomization -- or avoiding the phantomization altogether. This implies that theoretically there should not be any obstacles for extending the cosmological evolution beyond the corresponding singularities; therefore, such singularities can be considered a sort of a cosmological phase transition.

astro-ph.CO↗
arXiv2014

The possible resolution of Boltzmann brains problem in phantom cosmology

We consider the well-known Boltzmann brains problem in frames of simple phantom energy models with little rip and big rip singularity. It is showed that these models (i) satisfy to observational data and (ii) may be free from Boltzmann brains problem. The human observers in phantom models can exist only in during for a certain period $t<t_{f}$ ($t_{f}$ is lifetime of universe) via Bekenstein bound. If fraction of unordered observers in this part of universe history is negligible in comparison with ordered observers than Boltzmann brains problem doesn't appear. The bounds on model parameters derived from such requirement don't contradict to allowable range from observational data.

astro-ph.CO↗
arXiv2013

New exact cosmologies on the brane

We develop a method for constructing exact cosmological solutions in brane world cosmology. New classes of cosmological solutions on Randall-Sandrum brane are obtained. The superpotential and Hubble parameter are represented in quadratures. These solutions have inflationary phases under general assumptions and also describe an exit from the inflationary phase without a fine tuning of the parameters. Another class solutions can describe the current phase of accelerated expansion with or without possible exit from it.

astro-ph.CO↗
arXiv2013

Application of the Abel Equation of the 1st kind to an inflation analysis of non-exactly solvable cosmological models

In this paper we revisit the relationship between the Einstein--Friedman and the Abel equations to demonstrate how it might be applied to the inflationary analysis in a flat Friedman universe filled with a real-valued scalar field. The analysis is performed for three distinct cases of polynomial potentials. As a result of a numeric integration of Abel equation, the necessary and sufficient conditions for both slow-rolling and inflation proper are estimated with respect to the initial value of the field. In addition, the relationship between the slow-rolling condition and the inflation is ascertained.

gr-qc↗
arXiv2012

The cosmological constant as an eigenvalue of a Sturm-Liouville problem

It is observed that one of Einstein-Friedmann's equations has formally the aspect of a Sturm-Liouville problem, and that the cosmological constant, $Λ$, plays thereby the role of spectral parameter (what hints to its connection with the Casimir effect). The subsequent formulation of appropriate boundary conditions leads to a set of admissible values for $Λ$, considered as eigenvalues of the corresponding linear operator. Simplest boundary conditions are assumed, namely that the eigenfunctions belong to $L^2$ space, with the result that, when all energy conditions are satisfied, they yield a discrete spectrum for $Λ>0$ and a continuous one for $Λ<0$. A very interesting situation is seen to occur when the discrete spectrum contains only one point: then, there is the possibility to obtain appropriate cosmological conditions without invoking the anthropic principle. This possibility is shown to be realized in cyclic cosmological models, provided the potential of the matter field is similar to the potential of the scalar field. The dynamics of the universe in this case contains a sudden future singularity.

astro-ph.CO↗
arXiv2012

Equation-of-state formalism for dark energy models on the brane and the future of brane universes

Brane dark energy cosmologies, leading to various possible evolutions of our universe, are investigated. The discussion shows that while all these models can be made arbitrarily close to the standard $Λ$CDM cosmology at present, their future evolutions can be very different, even diverge with time in a number of ways. This includes asymptotic de-Sitter evolution, Little Rip with dissolution of bound structures, and various possible singularities, as the Big Rip, a sudden future singularity (Type II), and Type III and Type IV cases. Specifically, some interesting effects coming from the brane tension are investigated. It is shown, in particular, that the Little Rip occurs faster on the brane model than in usual FRW cosmology. And in the asymptotic de-Sitter regime the influence of the brane tension leads to a deviation of the value of the effective cosmological constant from that corresponding to ordinary dark energy. As a consequence, the value of the inertial force from the accelerating expansion can greatly exceed the corresponding inertial force in ordinary cosmological models.

gr-qc↗
arXiv2012

The Big Trip and Wheeler-DeWitt equation

Of all the possible ways to describe the behavior of the universe that has undergone a big trip the Wheeler-DeWitt equation should be the most accurate -- provided, of course, that we employ the correct formulation. In this article we start by discussing the standard formulation introduced by González-Díaz and Jimenez-Madrid, and show that it allows for a simple yet efficient method of the solution's generation, which is based on the Moutard transformation. Next, by shedding the unnecessary restrictions, imposed on aforementioned standard formulation we introduce a more general form of the Wheeler-DeWitt equation. One immediate prediction of this new formula is that for the universe the probability to emerge right after the big trip in a state with $w=w_0$ will be maximal if and only if $w_0=-1/3$.

gr-qc↗
arXiv2012

An Infrared Divergence Problem in the cosmological measure theory and the anthropic reasoning

An anthropic principle has made it possible to answer the difficult question of why the observable value of cosmological constant ($Λ\sim 10^{-47}$ GeV${}^4$) is so disconcertingly tiny compared to predicted value of vacuum energy density $ρ_{SUSY}\sim 10^{12}$ GeV${}^4$. Unfortunately, there is a darker side to this argument, as it consequently leads to another absurd prediction: that the probability to observe the value $Λ=0$ for randomly selected observer exactly equals to 1. We'll call this controversy an infrared divergence problem. It is shown that the IRD prediction can be avoided with the help of a Linde-Vanchurin {\em singular runaway measure} coupled with the calculation of relative Bayesian probabilities by the means of the {\em doomsday argument}. Moreover, it is shown that while the IRD problem occurs for the {\em prediction stage} of value of $Λ$, it disappears at the {\em explanatory stage} when $Λ$ has already been measured by the observer.

astro-ph.CO↗
arXiv2012

Phantom Cosmology without Big Rip Singularity

We construct phantom energy models with the equation-of-state parameter $w$ such that $w<-1$, but finite-time future singularity does not occur. Such models can be divided into two classes: (i) energy density increases with time ("phantom energy" without "Big Rip" singularity) and (ii) energy density tends to constant value with time ("cosmological constant" with asymptotically de Sitter evolution). The disintegration of bound structure is confirmed in Little Rip cosmology. Surprisingly, we find that such disintegration (on example of Sun-Earth system) may occur even in asymptotically de Sitter phantom universe consistent with observational data. We also demonstrate that non-singular phantom models admit wormhole solutions as well as possibility of big trip via wormholes.

gr-qc↗
arXiv2011

Quantum Creation of a Universe with varying speed of light: $Λ$-problem and Instantons

This article is dedicated to cosmologies with variable speed of light (VSL) - models, which one can consider as a particular case of models of a modified gravitation. In quantum cosmology the closed universe can spontaneously nucleate out of the state with no classical space and time. As known, in case of classical cosmology with varying speed of light $c(t)$ it is possible to solve the horizon problem, the flatness problem and the $Λ$-problem if $c=sa^n$ with $s$=const and $n<-2$. We show that in VSL quantum cosmology with $n<-2$ the semiclassical tunneling nucleation probability is $\emph{P}\sim\exp(-β^2Λ^k)$ with $β$=const and $k>0$. Thus, the semiclassical tunneling nucleation probability in VSL quantum cosmology is very different from that in quantum cosmology with $c$=const. In particular, it can be strongly suppressed for large values of $Λ$. In addition, we propose two instantons that describe the nucleation of closed universes in VSL models. These solutions are akin to the Hawking-Turok instanton in sense of O(4) invariance but, unlike to it, are both non-singular. Moreover, using those solutions we can obtain the probability of nucleation which is suppressed for large value of $Λ$ too. We also discuss some unusual properties of models with $n>0$.

hep-th↗
arXiv2007

A graceful multiversal link of particle physics to cosmology

In this paper we work out a multiverse scenario whose physical characteristics enable us to advance the following the conjecture that whereas the physics of particles and fields is confined to live in the realm of the whole multiverse formed by finite-time single universes, that for our observable universe must be confined just in one of the infinite number of universes of the multiverse when such a universe is consistently referred to an infinite cosmic time. If this conjecture is adopted then some current fundamental problems that appear when one tries to make compatible particle physics and cosmology- such as that for the cosmological constant, the arrow of time and the existence of a finite proper size of the event horizon- can be solved.

astro-ph↗
arXiv2007

Astronomical bounds on future big freeze singularity

Recently it was found that dark energy in the form of phantom generalized Chaplygin gas may lead to a new form of the cosmic doomsday, the big freeze singularity. Like the big rip singularity, the big freeze singularity would also take place at a finite future cosmic time, but unlike the big rip singularity it happens for a finite scale factor.Our goal is to test if a universe filled with phantom generalized Chaplygin gas can conform to the data of astronomical observations. We shall see that if the universe is only filled with generalized phantom Chaplygin gas with equation of state $p=-c^2s^2/ρ^α$ with $α<-1$, then such a model cannot be matched to the data of astronomical observations. To construct matched models one actually need to add dark matter. This procedure results in cosmological scenarios which do not contradict the data of astronomical observations and allows one to estimate how long we are now from the future big freeze doomsday.

astro-ph↗
arXiv2006

New "Bigs" in cosmology

This paper contains a detailed discussion on new cosmic solutions describing the early and late evolution of a universe that is filled with a kind of dark energy that may or may not satisfy the energy conditions. The main distinctive property of the resulting space-times is that they make to appear twice the single singular events predicted by the corresponding quintessential (phantom) models in a manner which can be made symmetric with respect to the origin of cosmic time. Thus, big bang and big rip singularity are shown to take place twice, one on the positive branch of time and the other on the negative one. We have also considered dark energy and phantom energy accretion onto black holes and wormholes in the context of these new cosmic solutions. It is seen that the space-times of these holes would then undergo swelling processes leading to big trip and big hole events taking place on distinct epochs along the evolution of the universe. In this way, the possibility is considered that the past and future be connected in a non-paradoxical manner in the universes described by means of the new symmetric solutions.

astro-ph↗